BA038 (B777) Thread

[petitb]

No comment on the probable cause, but the proposed revised operating procedures remind of my Tiger Moth days (1961); "when descending with throttle closed, regularly open throttle to rev engine". Trouble is, you guys no longer train on Tigers. :ok:

[chris weston]

Sun in my eyes 176p.

Sir,

(i) There is no way a normal landing could be made, ie reaching the runway.


Disagreed, if you read the whole thread and like many others I have, there are current 777 pilots out there and for whom I have great respect having read their postings over time, who claim to have made it to the runway in the sim using the data as published.

(ii) Agreed, this interim report confirms magnificent, intuitive and effective flying by the pilots in "less than a minute". Although we need to wait for the final report, this report should at least now stop any poisonous whispers to the contrary.

(iii) For the record I have been proven wrong by this report as I have speculated here that it was low Molecular Mass fuel components (hydrocarbon or the friends of ethoxy ethane as addditives) that caused the HP pump cavitation.

I have unequivocal respect for the AAIB and I need to think through the water ice explanation at the ppm level in fuel that is within spec.

The magic bullet flying oxygen cylinder retracing its steps as it exited the Quantas 747 and now this, reminds me not only to respect those slices of cheese but to show a little more humility.

CW

[FE Hoppy]

Tanimbar:

Having read the report twice now I concur with your analysis and in particular I'm drawn to the last conclusion. Ice accretion inside the wing fuel pipes over the two flights separating when the high fuel flow was demanded and causing the restriction. Where the restriction is is not clear but the face of the FOHE looks like a good bet.
They say that formation of the ice there was unlikely but don't comment on this being the collection point for ice formed upstream.
I'm sure we will see requirements for fuel feed line purging by high thrust demands coming to an AFM near you pretty soon.

[sooty655]

I think the previous posts questioning the temperatures reached within the pylon pipework may be significant.

In the refining and petro-chem industries, pipework which is subject to icing, waxing or similar problems is often trace heated. This is usually by steam or electrical heaters, but I guess a warm air bleed would also work.

Does anyone know if anything similar has ever been applied in aviation.

[Basil]

occasional,
There seems to be an assumption that the effective temperature within the wings is reasonably uniform and similar to or above the TAT.

From the latest Interim report:
On long flights the temperature of the fuel in the main wing tanks will tend towards the temperature of the boundary layer around the wing, which can be up to 3°C lower than TAT

One of the difficult to find and, I think, generically interesting pieces of information to emerge from this investigation.

[Hotel Mode]

On long flights the temperature of the fuel in the main wing tanks will tend towards the temperature of the boundary layer around the wing, which can be up to 3°C lower than TAT

One of the difficult to find and, I think, generically interesting pieces of information to emerge from this investigation.

Dont think thats new, its been in the manuals for as long as i can remember.

[GlueBall]

chris weston: "there are current 777 pilots out there and for whom I have great respect having read their postings over time, who claim to have made it to the runway in the sim using the data as published."


No simulator has true airplane fidelity.

No simulator has true airport environs and runway fidelity.

It's not an argument. Just a statement of fact. :ooh:

[awblain]

It would be interesting to hear whether they reached past the grass on the
first attempt, or after a few tries.

Given the available energy, I find it hard to believe a crew being able to
make it to the concrete. However, details of how different strategies played
out might be interesting. I don't remember reading such a post.

If they set up the sim just to try BA038, then they were in a much better
position than the real crew: they knew the exact problem to expect, had
seen the true outcome, and no lives were on the line. A true test would be to
spring BA038 rollback on crews when their configuration and energy
matched in the simulator, and see how they did first time, building up
data slowly.

For what my view's worth: getting BA038 over the fence, stopped
and evacuated with only a single serious injury onboard and none on the
ground - for real - deserves much respect.

[nhs]

El #

From posts since mine your claim from "not-easy-to-dismiss" sources" appears to have been dismissed.
And please don't be so dismissive of me. I have read all post & also the one you suggested.

Your statement re: dead stick landings also appears to be incorrect. "sheer luck" Well I dont think so. Ok I'm just SLF but my view was reflected by suninmyeyes in post 1765.

My trust in flying has not been decreased by this, in fact has been increased. I trust the people I fly with. I also trust the AAIB to get to the bottom of this no matter however much speculation there might be on this site.

My bottom line was reflected by suninmyeyes. "A manual landing was achieved in which all the passengers survived" For that I thank & respect the crew. I'd rather have been on BA038 than the Madrid flight.

[M.Mouse]

It would be interesting to hear whether they reached past the grass on the first attempt, or after a few tries.

Post #121 in this thread answers your question.

http://www.pprune.org/rumours-news/334267-ba038-crew-get-ba-safety-medal-7.html#post4322326

[el #]

nhs, please look at the post mentioned above and others in the same page.

Please understand that I agree 100% with the what M.Mouse, a Pilot, says: it would have been superhumane to land succesfully in these conditions, in other words even if it would have been theoretically possible, nobody can expect an unprepared crew to accomplish.

Anyway for the last time, if anyone wants to believe that it was a manual landing, OK with me, but it was not.

[ChristiaanJ]

I have read the latest AAIB report.

Water content of the fuel seems to have been established from fuel samples after the crash.

According to the AAIB and other reports, most of the remaining fuel was spilled and only a few tons remained.
Somebody, many hundreds of posts ago, suggested that, with water being heavier than fuel, under the circumstances a lot of water could already have drained from the aircraft by the time the fuel samples were taken.

Question: might there have been a lot more water than quoted in the AAIB report?

CJ

[CONF iture]

At last ... some official indications on crew actions ...

28 sec before impact thrust levers were partially cycled
16 sec before impact flaps were raised from 30 to 25 (you was correct M.Mouse !)
8 sec before impact FO pushed the control column

At that time AP disconnected, pitch attitude was 14 deg up, anyone to determine the AOA ?

Flight idle fuel flow looks to be around 3000 pph per engine ... surprised that 6 and 5000 pph did not bring the aircraft a bit further ?

Note: Right FF maintained pretty stable at 6000 pph when Left FF reduced from 5 to 4000 pph in the last 15 sec

[snowfalcon2]

Boeing is releasing new operating procedures to deal with the BA038 icing threat, according to this newspiece in FlightGlobal. (http://www.flightglobal.com/blogs/unusual-attitude/2008/09/british-airways-777-crash.html)

Interestingly, they seem to concentrate on the "ice blocking heat exchanger" scenario and not the "ice accretion in the pipes" scenario.

[Charles.]

Glue Ball,

Increasing AOA to stay on the glide until the stick shaker is activated ( what the autopilot did according to the AAIB report ) is definitely not the way to get the best chance of making it to the runway... It is a fact, simple fly mechanics. Stall speed is certainly not the best gliding speed.

Therefore, considering that the plane missed the runway by a reasonably short distance, it is not a surprise that a pilot WHO KNOWS WHAT IS GOING TO HAPPEN, i.e. that the thrust will never come back, could be able to land the plane on the concrete by immediately taking the right speed, slope, and wing configuration. So, i am pretty confident that the simulation may be quite relevant.

That doesn't mean that the real pilots on the real flight were wrong in their actions, they had no way to guess what was to happen in the next seconds...

And in fact, they saved the day by pushing the stick and reducing flaps as soon as the situation became clear.

[awblain]

Re: my question 1778 http://www.pprune.org/rumours-news/340666-ba038-b777-thread-89.html#post4375609, your answer 1780 http://www.pprune.org/rumours-news/340666-ba038-b777-thread-89.html#post4375780, linking to http://www.pprune.org/rumours-news/334267-ba038-crew-get-ba-safety-medal-7.html#post4322326

Indeed it does answer my question, M.Mouse. Thanks.

I didn't think of exploiting ground effect to boost lift: the picture of a glider/skydiver landing didn't jump into my mind when imagining their 777 over Hounslow.

If I may ask, how did it work out for you on the `several attempts' prior to using the recipe you posted on the `medal' thread for reaching the threshold in the simulator?

[guclu]

Hi all,

in the report iy says there are three tanks on 777.

Im a 340/330 guy and just wondering if there ain't any outboard tanks inside the wing tanks.

In the 340/330 there is an outboard tank which usually has around 2500 kg of fuel. This fuel is kept near the edge of the wing to help reduce the moment of lift at the wings. The coldest fuel is most of the time in this tank and this tank usually will be used at the end of the flight when all other fuel is used.

My questions for the 777 experts:

1) Is there a small tank like this at the edge of the wing ?

If yes

2) is there a fuel temperature sensor for this tank on the 777 ?

Regards,

Guclu

[Rightbase]

An impressive AAIB report which I am sure will reward more study.

For those unhappy that an extremely unlikely event should affect two independent systems within a few seconds of one another - there is a common factor over and above the shared history of those systems. The centre tank which is supposed to be empty, but is still in the loop.

The previous flight is significant because with ground temperatures in Beijing below zero, any ice from the outbound flight would not be scavenged.

The fuel uploaded in Beijing was warm enough to have melted this into droplets; the behaviour of the resulting droplets in terms of their size, accretion rate and so on, in the centre tank of an aircraft at rest in a below zero environment is problematic, but if it froze again before start-up, the water scavenge, and later the fuel scavenge would not get it. It would not start to melt and move from the 'empty' centre tank until the warmer environment of the descent.

So there is the credible possibility that at some time in the descent a melt surge presents ice, wateer and/or slush at the centre tank fuel scavenge points, and is then fed to the main tanks to be refrozen as it makes its way down to the boost pumps .....

If this happens during an unusually prompt arrival at late finals on a cold winters day, another hole lines up.

It would be particularly concerning if a procedural attitude or acceleration change could trigger such an episode which then prompts a temporary fuel restriction episode timed to coincide with a critical procedural need for more power.

Since the AAIB work is continuing, they must believe further recommendations are a possibility.

[FE Hoppy]

I think the idea is that the ice forms in the pipes and collects on the face of the heat exchanger. The procedures attempt to dislodge the ice before enough builds up to cause a problem. I can see the need to do the powerback and wait(hope) shortly after the pre descent power up!!

[Basil]

Hotel Mode,
Dont think thats new, its been in the manuals for as long as i can remember.
Never seen it - guess I stopped flying before you started. Last time I asked Boeing they couldn't help.

[Captain Big Iron]

Barit 1 said:

I'm not sure this adds up. The "amazingly efficient" Trent with more spools, and more bearings, probably has more heat generated in the oil, and thus any "stagnating" fuel will be exposed to more BTU transfer, leading to LESS probability of icing in the fuel-oil heat exchanger.

Often the most severe design point for the cooler is early in descent, when lube heat rejection is still high, yet fuel flow (the heat sink) is very low.



I agree with Barit1 here,

The solution to an Hi temp light coming on in the decent (which is not uncommon) for many twin-spooled engines is to push up the power and throw out the boards, because those are fuel-cooled oil systems: the increased fuel flow (higher than idle) cools the oil system and the light goes out. No need to write it up since you just fixed the problem.

The point here being: decent at idle is a high-temp situation; not a freezing situation. I know that sounds backwards, but for most of the seven transport types I flew that is true.

However, the heat exchanger is no doubt regulated by another computer chip on this tripple spooled model. More complexity equals more unreproducible, unpredictable results.

This accident already is shaping up to be another 737-Rudder, 747-center-fuel-tank mystery.

Blaming icing by itself seems unlikely to me. The 747SP flew up to 45,000 feet for 26 hours routinely for thirty years and never had any problems (that I know of.) It even completed a 54 hour flight. KC-135's B-52's and airborne command posts have remained aloft for days without any problems.

Tanimbar said:
On another matter. The AAIB interim report states (Water ice in fuel, p12),

Quote:
As the fuel temperature is further reduced, it reaches the Critical Icing Temperature, which is the temperature at which the ice crystals will start to stick to their surroundings. When the fuel temperature reduces to approximately ‑18°C (0°F), the ice crystals adhere to each other and become larger. Below this temperature little is known about the properties of ice crystals in fuel and further research may be required to enable the aviation industry to more fully understand this behaviour.
I read this with disbelief. The words, "little is known" is, well, shocking.

Until today I had thought that the industry had fully experimented, tested and evaluated the effects of temperature on fuel (at all operating ranges).

By the way, my money is still on stratification ( no, don't respond to this; I need to read the report more carefully and may change my mind).

Regards, Tanimbar


I agree Tanibar and others, this is a shocking statement and makes me wonder how other airframes have stayed aloft for over a quarter of a century with no icing problems. Prist type additives? The 747SP (which I merely jumpseated) has nine tanks and surely runs into this problem up in the 40's. But all of the aircraft I mentioned (747SP, B-52, KC-135, 747-EAC-1) were non-FADEC (before engine upgrades) and their safety records were based on direct-link hydro-mechanical designs.

The FADEC is usually the culprit when you are discussing rollbacks. A pilot with a control cable would keep trying to clear the ice out by trial and error. A FADEC goes back to idle and tries to reboot a start sequence.

JMHO's only.

[vapilot2004]

I was happy to see the cavitation marks mystery solved. :ok:

I suppose this blows the electronic/computer glitch theories out of the water finally.

The idea that a computer or power failure could shutdown both engines
might be possible on some aircraft, but not this one.

From http://www.pprune.org/3852203-post176.html posted by a handsome fellow I know well.

:8

[sispanys ria]

Interesting report. It's mentioning twice that the CVR worked and nothing much. I'm glad it worked but I guess it could be even more interesting to have some details about its content.

According to the FDR the captain retracted the flaps to 25 at 240 ft resulting in increasing the pitch up attitude while the AP was already pulling on the nose to follow the glide until reaching 14 degres nose up. The AP finaly disconected following the stick shaker when the FO pushed on the stick at 170 ft and around 100 kts.

Usualy retracting flaps in dead stik approach is associated to a nose down command and speed increase, not the contrary.

[Eldin]

One of the reasons that interim procedures published by Boeing apply only to Trent 800 powered 777s could be differences in design between the two engines. (See Boeing 777 FCOM)


Fuel System, Flow Path:
Trent 800:
1st Stage Engine Driven Fuel Pump
Fuel/Oil Heat Exchanger (FOHE)
Fuel Filter
2nd Stage Engine Driven Fuel Pump
Fuel Metering Unit (FMU)

GE90
1st Stage Engine Driven Fuel Pump
2nd Stage Engine Driven Fuel Pump
FOHE
Fuel Filter
FMU

This means that on GE90 engines the fuel has already gone through the second stage (HP) fuel pump before it enters the FOHE, which will cause some rise in temperature



Oil System, Flow Path:
Trent 800:
Oil Pump
HP Oil Filter
Air/Oil Heat Exchanger
FOHE


GE90:
Oil Pump
HP Oil Filter
FOHE
Backup Gen Oil/Oil Heat Exchanger

That means that in Trents the oil has already part of the heat extracted in the air/oil heat exchanger before it makes its way into the FOHE.




No conspiracy theory required after all?

[ZAGORFLY]

is the 5th report, and still the reason od that reduced fuel flow is unclear.

interesting report anyway but:
1) I was surprised to read that such approach was conducted in Autopilot. It would seams that they had other problems to handle if they decided to perform an auto land.
2) I was surprise by the action (desperate i believe) of the commander reducing the flap setting and continuing to keep the plane in autopilot,
3) I was surprise that the crew failed to anticipate the stick shaker situation (they do not have an Alpha floor protection)
4) I was surprise that the A/P was disconnected only by the F/O that apparently pushed the column into the Eicas (as supposed to do)

since the only possible obstruction was up stream of the HP pump It looks like the B777 needs like a Cessna a hot hair (to the carburator) swith, or some Aspirine in the tanks to reduce the piping cholesterol of this giant plane.

[NigelOnDraft]

ZAGORFLY

1) I was surprised to read that such approach was conducted in Autopilot. It would seams that they had other problems to handle if they decided to perform an auto land.
2) I was surprise by the action (desperate i believe) of the commander reducing the flap setting and continuing to keep the plane in autopilot,
3) I was surprise that the crew failed to anticipate the stick shaker situation (they do not have an Alpha floor protection)
4) I was surprise that the A/P was disconnected only by the F/O that apparently pushed the column into the Eicas (as supposed to do)

1. They were not performing an "autoland". They were performing an autocoupled approach to disconnect at some point prior to a manual landing. Like probably 99%+ of airline approaches...
2. The Final Flap setting (30 for 777, Full for Airbus etc.) is largely all drag... You describe it as desparate... most would describe it as inspried and almost certainly saved many lives. Training nowadays is almost 100% directed towards using the AP with a problem - not disconnecting it.
3. They did not "fail to anticipate" the stick shaker... they had already selected full thrust many seconds before :ugh:
4. I doubt the SFO "pushed the CC into the EICAS" - nor do I think that is the laid down drill in the QRH/FM :{

IMHO you and many others are wasting your time dissecting what the crew did (or did not do). They did a damn good job, working outside the box, but not excessively so, whilst trying to correctly troubleshoot the problem(s). Assuming you are even a pilot (?) since when do you practice stall recoveries close to the ground AND with zero power... it is not taught in anything (other than a glider?) since it is negative, improbable and inapproriate.

We do train for engine failures, and we do train for stall recoveries (but with power, or at least height).

This inquiry, IMHO, is 99% concentrating on WHAT caused the power failure(s), and preventing future occurances... in the short term by determining the circumstances and avoiding then, and in the longer term by design. I think it unlikely more than a fraction of the final report, and probably none of the formal recommendations, will be on crew actions / extra training to deal with essentially a double engine failure at ~2NM :ooh:

NoD

[philipat]

Captain Big Iron:


Blaming icing by itself seems unlikely to me. The 747SP flew up to 45,000 feet for 26 hours routinely for thirty years and never had any problems (that I know of.) It even completed a 54 hour flight. KC-135's B-52's and airborne command posts have remained aloft for days without any problems.




Also Concorde comes to mind. I know that the Investigation team is of the very best and the report is extremely thorough. But still, after millions of flights by both 747 and 777 aircraft on these routes in similar conditions, it does seen strange. I suppose that on this particular flight the holes in the Swiss cheese slices just happened to align perfectly?

There have been several other reports of 777 aircraft having engines not respond to commands in situations where ice is not likely to have been an issue. To those familiar with the 777, did these incidents also involve RR Trents and have these incidents been adequately explained?

[keel beam]

I am surprised this has not been more in the forefront of thoughts. I cannot say specifically for the B747SP, but certainly for the "classic" B747 and going back a few more years, the B707, they had dedicated fuel heaters. these were switched on by the flight engineer if he had a Fuel Filter Block warning light. After a set period of time, the fuel heater was switched off.

Looking at the diagrams on this thread, fuel heating is only supplied by the Fuel/Oil heat exchanger.

Just a thought ....

[Fragman88]

Just my 2C,

If the AAIB are prepared to go public on a very probable icing issue here, after my 15,00hrs, much of it Ultra Long Haul, albeit on B747s, I will believe them.

The crew actions can be second guessed forever, but after the Schipol freighter double engine failure and loss a few years ago, we tried it (As I'm sure most 747 operators in the world did) in the sim.

Being fully aware of the preliminary reports, doing a briefing, and configuring the sim as best we could to simulate the conditions experienced by the crew, it took me, as a Training Captain, 4 tries to achieve even a marginally survivable result----and this was not at the end of a 15 hour day.

Re a previous post, from my recall, the 747 at F25 required an increase of pitch of about 1.25 degrees above that for F30, but with a significant decrease in power required i.e. drag, so good call there for the flap reduction.

Well done crew.

As an aside, from the later pictures, it would appear that a significant part of the A/C was on the piano keys, so it wasn't really a short landing, just an early touchdown.

I'll get my coat.:D

[stickyb]

Question from a non pilot.

When a liquid is compressed, temperature rises. When pressure reduced, temperature falls.

How is the flow of fuel controlled (physically, not logically) ?

Would it be possible for the 'valve' controlling the flow to form a point at which pressure was reduced, thus cooling the fuel even more and maybe causing ice to aggregate?

A small restriction could then, under some circumstances, become self perpetuating

[M.Mouse]

Also Concorde comes to mind.

Concorde had the opposite problem in the cruise, its tip probe temperature was the governing factor. Concorde's TAT was high at supersonic speeds. Cold fuel was not an issue.

[The late XV105]

The 747SP ... <snip as irrelevant> ... even completed a 54 hour flight

Not exactly so.

To celebrate the 50th anniversary of Pan Am, flight 50 as it was called flew a route from and to San Francisco that indeed took 54 hours, 7 minutes, and 12 seconds to complete but it was actually comprised of multiple sectors. Stopovers were at London Heathrow, Cape Town International, and Auckland Airports.

[Desk Jockey]

Question from a non pilot.

When a liquid is compressed, temperature rises. When pressure reduced, temperature falls.

How is the flow of fuel controlled (physically, not logically) ?

Would it be possible for the 'valve' controlling the flow to form a point at which pressure was reduced, thus cooling the fuel even more and maybe causing ice to aggregate?

A small restriction could then, under some circumstances, become self perpetuating



I think you’ll find you can’t compress a liquid.

[Lurking123]

I think you will find that you can compress a fluid although the visible effect is minute compared to gas/vapour. Indeed, a compressed fluid is less viscous than one which isn't compressed. That said, the values concerned are so small it is not worthy of any serious discussion.

[Green-dot]

Posted by ChristiaanJ, ref. post #1782:


Somebody, many hundreds of posts ago, suggested that, with water being heavier than fuel, under the circumstances a lot of water could already have drained from the aircraft by the time the fuel samples were taken.

Question: might there have been a lot more water than quoted in the AAIB report?


Please read the report(s) again.

AAIB interim report G-YMMM, Page 2, second column:
"The aircraft had previously operated a flight on 14 january 2008 from Heathrow to Shanghai, with the return flight arriving on 15 January 2008. The aircraft was on the ground at Heathrow for 20 hours before departure to Beijing on 16 January 2008."

AAIB interim report G-YMMM, Page 13, first and second column:
"G-YMMM was last sumped at Heathrow on 15 January 2008 prior to the flight to beijing. The aircraft had also been sumped at London heathrow whilst on maintenance, on 14 January 2008."

"Prior to the accident the operator had initiated a review of the effectiveness of their [water] sumping programme, . . . . . ., a number of aircraft were checked in a warm hangar where any ice in the fuel tanks would have melted and migrated to the drains. G-YMMM was sumped in this manner on 14 December 2007. The review established that whilst the free water does freeze and could occasionally block the tank drains, there was no evidence of any significant quantities of free water having accumulated in any of the 43 Boeing 777 aircraft."

AAIB Special Bulletin S1/2008, first column, Page 5:
"The aircraft's [G-YMMM] fuel tanks were last checked for water in the fuel on the 15t January 2008, this was prior to it's refuelling for the outboard sector to Beijing."

With the aircraft on the ground for 20 hours and a review programme in place, wouldn't it be logical that sumping on 15 january took place at a time it was estimated that any ice in the tanks had melted before sumping commenced? Especially with the aircraft on the ground for 20 hours and temperatures well above freezing (as records of those dates indicate) and sumping taking place before refuelling. The interim report does not mention how many hours after arrival from Shanghai water sumping was performed but to my knowledge this is done immediately prior to refuelling? Refuelling probably took place any time after the payload, flight planning and weather for the flight to Beijing were known, so this would have happened perhaps only a few hours (but still on 15 January?) before departure?

If so, and water sumping was done correctly, there would be very little water in the tanks. This, together with sumping on 14 january during maintenance should imply the tanks were virtually free of water as G-YMMM departed to Beijing.


After reading the report several times, although it is very informative, new questions regarding the aircraft systems and engines surfaced for me which i shall digest for a while.

The emphasis is now focussed on ice. 5 liters of water diluted in approx. 100.000 liters of fuel . . . . and a lot of data mining.

I'm sure they will find the facts, the evidence, and the reasons why in the near future. I hope they are not barking up the wrong tree.

The investigation, although very detailed and thorough, gives me the impression of trying to castrate a fly with boxing gloves on :uhoh:

Green-dot

[HarryMann]

I am pretty sure at the beginning of the BA038 speculation threads, people were talking about the possibility of 100's of litres in not 100's of Kgs of water potentially being present, at least in the centre tank, as the norm? What's changed, or was this gross misinformation?

[simflea404]

...and the mass of 1 litre of water is...Doh!:ugh:

[dxzh]

What a fascinating interim report - illuminating and in plain English. I would like to highlight a few points which might be good to see addressed (or dismissed) in more detail in due course:

1. Cold soaked main tank fuel from previous sector

Figure 1 seems to indicate that just prior to the uplift of fuel in Beijing the temperature of the 4 tons or so of fuel in the left hand main tank which was left over from the previous sector was -20˚C. Even after the uplift of warmer 5˚C fuel in Beijing the left main tank temperature never appears to rise above -1˚C. If temperature is as relevant as suggested, then a body of fuel from the previous sector remaining at -20˚C seems noteworthy as a possible contributory factor leading to the potential subsistence and continued development of accretions of ice in at least those parts of the main tank fuel system which remained at or below 0˚C.

2. Prolonged fuel scavenge operation

The interim report currently seems relatively silent on a key design feature of the 200ER as compared to certain other Boeings - namely, the relative size of the centre tank and the prolonged operation of the fuel scavenge.

The data (in Figure 1) shows that the remaining 800kg of centre tank fuel to be scavenged once the main tanks contained less than 12.5 tons started a little under 3 hours before landing and was finished within 30 minutes.

Given the apparent ability of each of the two centre tank fuel scavenge pumps in G-YYYM to suction fuel at a rate of some 0.8 tons per hour into each main tank, could there be any unintended consequence (which would normally have no bearing on safe flight absent some of the other contributory factors present that day) as a result of them running “dry” for over 2 hours once the remaining 800 kg was indicated to have been scavenged (and similarly on previous sector)?

After remaining 800 kg of fuel was scavenged, would not the fuel scavenge pump, being a jet pump, scavenge air? What volume of air would be entrained/dissolved into fuel in each main tank over remaining 2.5 hours of flight given powerful nature of scavenge pump? The centre tank is open to the atmosphere so any air sucked out would be immediately replaced. Presumably entrained/dissolved air in main tank fuel would be subsequently released as part of dynamic process given low pressure at height? Could this entrained/dissolved air end up in the fuel manifold and be released in a manner which would cause the potential failure of the suction feed or the override/jettison pump valves to open? As the suction feed in the climb at least seems to have a known failure mode from vapour lock (see previous posts) arguably the interim report’s understandable assumptions as to the location of a restriction might need to be reconsidered slightly if it could be shown that the suction feed might be vapour locked and/or (even more speculatively but for a similar reason to the suction feed) air might not be drawn in from the centre tank. Fuel testing after the event would not be able to establish the existence (or absence I accept!) of any air saturation dynamic and any vapour lock would be long gone. NB: my point is limited to expanding the possible locations of the icing restriction as I note the comments about aeration not being the cause of the cavitation in the HP pump.

As regards the 800 kg remaining shallow layer of fuel in the centre tank, is there any temperature or other information as to potential stratification in the 5 hours or so that it sat in a largely empty, cold still tank after OJ pumps selected OFF? Does the 0.14 max litres of water from condensation reflect turnover (if any) of atmosphere in the centre tank as a result of the operation of the fuel scavenge pumps in the last 3 hours of the flight (or the earlier sector)? Might there be any concentrations of water from accreted ice melting in the later stages of flight? Would slugs of water scavenged from centre tank be more likely to result in any particular form or size of ice crystal more susceptible to accretion when swept into main tanks? If ice had also previously accumulated and not melted on previous sector into Beijing could this be a contributory factor? The AAIB’s comment re unknown fluid dynamics seems spot on and not easily resolved given the complexities of the many different variables (eg Jet A1, ice, temperature, pressure, airframe, geometry, timing etc). Testing showing only 40ppm of water makes explaining the degree of icing sufficient to cause a restriction (sorry two restrictions), but not subsisting in any quantity in the main tank fuel, the mother of all tortuous theories though.

One relatively simple precautionary safety recommendation might be (eg as per certain other Boeings) to require the motive flow to the centre tank fuel scavenge pumps in 200ERs to be cut off after 30/40 minutes of renewed operation. Continued scavenging is unnecessary and might be a necessary contributory factor in lining up the holes in the two swiss cheeses (two cheeses, given must be at least one restriction on each side of the fuel system).

Alternatively, the fuel system test rig should perhaps also attempt to take account of what effect each fuel scavenge pump might have on fuel in the main tanks and the fuel supply system leading out of them?

3. Statistical significance of duplicated restriction in two independent fuel systems

The comment on page 19 of the interim report that "This is the first such event in 6.5 million flight hours and places the failure as being 'remote' as defined in EASA CS 25.1309" perhaps does not do justice to the statistical significance of what happened. While the statement may be correct, it could be seen as overstating the remoteness of the "event" - in particular, given the sharpened awareness from the data-mining that the particular environmental factors relevant to this event have occurred in but a few of those many flight hours and the fact that the current strawman is dependent on there being two separate duplicated events, i.e. one restriction in each independent fuel system, with assumed common contributory factors.

Also, if I may quibble with what may have been unintentionally implied by the word “remote” in the context of EASA CS 25.1309, when is a double engine rollback on a twin engine aircraft at very low altitude over a highly populated area caused by a restriction to the fuel supply to each engine limiting effective supply to about 15% or so of the certified maximum just a “major failure condition” for which “remote” is the relevant test, rather than a “hazardous failure condition” or a “catastrophic failure condition” which have to meet stricter standards? It would seem extraordinary to play down the significance of this demonstrated and duplicated failure condition, even if the improbability of its recurrence is in question.

4. Indications, annunciations and corrective actions

Also in the context of that same EASA CS 25.1309, which states in paragraph (c) (just read it at http://www.aaib.gov.uk/sites/aaib/cms_resources/JY-JAR%20Appendix%20B.pdf) that:

“Information concerning unsafe system operating conditions must be provided to the
crew to enable them to take appropriate corrective action. A warning indication must
be provided if immediate corrective action is required. Systems and controls, including
indications and annunciations must be designed to minimise crew errors, which could
create additional hazards.”

would it not be helpful and practical (and perhaps necessary) to introduce an immediate warning and annunciation of the discrepancy between the Actual EPR and the Commanded EPR as soon as the more normal 2-3 second lag becomes a clear discrepancy as at about second 154[95] (in figure 2), rather than requiring crew to observe the discrepancy and establish if it is “just” a glide slope, autothrottle or other issue – even more so by second 160[95] when both engines are rolling back.

Needless to say, the crew did the most remarkable job – and this seems more apparent as the background unfolds and you look at how little time and room they had to act.

[DC-ATE]

Pardon me if this has already been discussed (I just joined), but glancing through the previous posts as best I could looking for remarks on what the pilots did in the final moments, I couldn't find what I was looking for.

What are the thoughts of those pilots on here about the Captain (I believe it was) REDUCING the flap setting after realizing their problem of maybe not making the runway? Seems to me this aggravated the problem by INCREASING the stall speed, therby requiring the F/O to lower the nose, thereby making it impossible to reach the runway.

[Basil]

What are the thoughts of those pilots on here about the Captain (I believe it was) REDUCING the flap setting after realizing their problem of maybe not making the runway?
A master stroke :ok:
The last stage of flap is almost all drag with little contribution to CL (coefficient of lift) so he immediately got rid of some drag.
The go-around procedure on, e.g., the B747 is - max thrust, flap 20 (jus' like that!) and you don't drop out of the sky but transition instantly to a high energy situation partly by getting rid of drag which has permitted you to keep the engines spooled up just for that eventuality.

[HarryMann]

...and the mass of 1 litre of water is...

1 Kg! Oops :O

[Smilin_Ed]

Would it be possible for the 'valve' controlling the flow to form a point at which pressure was reduced, thus cooling the fuel even more and maybe causing ice to aggregate?While it might be possible, in this case, the restriction has been shown to be upstream of the HP pump and thus even further upstream of the Fuel Metering Valve.

[ChristiaanJ]

Green-dot (post #1805),
Many thanks for taking the AAIB report apart more carefully than I did.

However, how effective is sumping? The report quotes no figures, just the conclusion from the review: "there was no evidence of any significant quantities of free water having accumulated..."

And also "If so, and water sumping was done correctly, there would be very little water in the tanks. This, together with sumping on 14 january during maintenance should imply the tanks were virtually free of water as G-YMMM departed to Beijing."

All this is qualitative, not quantitative, which made me wonder whether we were talking about 5 ltrs, 20 ltrs or 100 ltrs being "significant" or "virtually free of water"..

But, going back to the report, the amount of water estimated in the Bejing fuel upload was in the order of 40 ppm (the 5 ltr quoted). The samples taken after the crash were in the same order.
So, for the moment, it looks as if I'm barking up the wrong tree.

Bedankt, Green-dot!

CJ

[Swedish Steve]

And also "If so, and water sumping was done correctly, there would be very little water in the tanks. This, together with sumping on 14 january during maintenance should imply the tanks were virtually free of water as G-YMMM departed to Beijing."

All this is qualitative, not quantitative, which made me wonder whether we were talking about 5 ltrs, 20 ltrs or 100 ltrs being "significant" or "virtually free of water"..

I sump fuel tanks on aircraft. We drain out about a litre into a clear plastic container, and you might see a globule at the bottom of the bottle, less than 1cc. Sometimes you find nothing. So a decilitre would be significant, and 5 litres cause for an investigation.

I also work in Sweden, we do not sump tanks when the OAT is below zero. Bit silly really, but ice will not come out!!

[Nopax,thanx]

I don't know if anyone else caught this little gem in the letters page of today's Telegraph;

Letters to the Telegraph

6 September 2008

De-icing aeroplanes

SIR – As a frequent flier with smaller aircraft, I know that it is common knowledge among pilots that condensation builds up in fuel tanks. This water sinks to the bottom of the tank and must be periodically drained to avoid it being drawn into the engine.

One would assume that ice forming in the fuel lines of a big jet (report, September 5) indicates that there’s too much water around and that someone hasn’t been doing their job properly.

Roger West, Appenzell, Switzerland


Why the hell didn't anyone else think of that......:rolleyes:

[ExSp33db1rd]

#1796

Nigel on Draft " Absolutely - the crew were faced with a totally new experience and did their best, magnificently. I'm not sure I would have had the courage to even touch the flaps at that stage, and just thankful that I was never placed in that situation.

To the guy who suggested that draining a thimble full of fuel out of something like a Cessna 152 bears any relation to what might have happened .............. !! Why do I even bother to respond !! :ugh:

[Nopax,thanx]

I thought it would go down well here....it certainly made me chuckle!! Save us from the experts, eh?

[PAXboy]

Non-pilot speaking.

Since the new interim report, a couple of people have asked "5 liters of water diluted in approx. 100.000 liters of fuel" and how that could cause the failure.

As I have understood it - that is not what is being suggested. The failure may have occurred because of ice and other particles resulting from the low temperatures. There has been much talk (in PPRuNE) about stratification of the fuel and that a 'dollop' of fuel thickened but not frozen.

Unless I much mistake, no one is saying that a small amount of pure iced water caused the loss of thrust. I sit to be corrected.

[DC-ATE]

Basil -

"The go-around procedure on, e.g., the B747 is - max thrust, flap 20 (jus' like that!) and you don't drop out of the sky but transition instantly to a high energy situation partly by getting rid of drag which has permitted you to keep the engines spooled up just for that eventuality."

Similar with all jet transports. But.....you have the engines spooled up. In this case they were basically without power. Not sure I'd want to touch anything.

[bucket_and_spade]

PAXboy,

The answer you're after is detailed in the interim report!

B&S

[Green-dot]

Swedish Steve,


I sump fuel tanks on aircraft. We drain out about a litre into a clear plastic container, and you might see a globule at the bottom of the bottle, less than 1cc. Sometimes you find nothing. So a decilitre would be significant, and 5 litres cause for an investigation.


As I have sumped fuel tanks on aircraft many times and with similar findings as you discribe. Most of the time there was no visual indication of water what so ever. The odd every-now-and then somewhere around that 1 cc you mentioned. Never experienced more than that.

Indeed, finding 5 liters of free water during a transit check (certainly when sumping is performed on a daily basis) is reason for an investigation.

The estimated 5 liters of water in the fuel loaded at Beijing, according to the report, was divided into 3 liters of dissolved water and 2 liters of undissolved water (entrianed or free, spread evenly over the main tanks and the center tank), plus perhaps a maximum of 0.14 liter which may have entered via the fuel tank vent system during the flight.

If evenly spread, that would imply a maximum of approx. 0.7 liter per main tank and center tank regarding entrained or free water in the fuel as loaded in Beijing. Main tanks probably a bit more than 0.7ltr and the ctr tank a bit less when compared to the fuel quantity loaded in each tank.

When the aircraft's fuel pumps are activated, most of the dissolved and entrianed water/ice would have been well stirred and consumed during the flight, with the aircraft sumped twice the previous few days, how much water would have had time to actually settle at the bottom of the tanks to form a layer of ice? And if so, if that estimated small amount broke loose or melted into slush, wouldn't it have blocked the water and/or fuel scavenge pumps before it could have collected somewhere in the boost pumps or engine feed manifolds?

After take-off at Beijing the fuel temperature remained -2 deg. C until reaching initial cruise altitude, as measured by the probe in the LH main tank. With the center tank above the airconditioning packs would it be possible that the local fuel temperature was slightly warmer at the bottom of the center tank during this flight phase, melting any ice at the bottom into water which would have been a very small amount, if any at all, as estimated in the report?

If so, wouldn't most of it have been scavenged by the ctr tank water scavenge pumps, subsequently well stirred by the OJ pumps and have been consumed with engines set at climb power before doing any harm?

Another question is, if the fuel temperature in the above scenario remained below 0 deg. C, but with an almost empty center tank (situated above the airconditioning packs), what would the temperature be at the bottom of the tank with the 800kg of fuel remaining for approx. 5.5 hours before those 800kg were scavenged? Would the temperature have reached above 0 deg. C, melting any ice which would have been scavenged as a mix of fuel/slush/water but well stirred after passing the boost pumps before re-freezing again in the engine feed manifold? (ctr tank OJ pumps are off at this stage, therefore water scavenge pumps in the ctr tank are off) Or would the ice have melted at lower altitude after the ctr tank was empty and then scavenged? (max. 0.3 liter LH and 0.3 liter RH in the ctr tank) Any free water at the bottom of the main tanks would probably have remained frozen until touchdown and would not have moved much, even if it broke free, due to the dihedral of the wing lower surface. The picture taken of the aircraft with frost on the wing lower surface seconds before touchdown may be evidence to that.

I find it hard to believe such small amounts of free water/ice in the ctr tank, which has a flat lower surface, would have been distributed so evenly between LH and RH engine feed systems with an aircraft in motion to contribute to the cause of identical problems within seconds to both systems.

The 3 liters of dissolved water in the fuel, however, might have but the question remains, wouldn't we have experienced such events more frequently?


Green-dot

[sispanys ria]

Quote:
What are the thoughts of those pilots on here about the Captain (I believe it was) REDUCING the flap setting after realizing their problem of maybe not making the runway?
A master stroke http://static.pprune.org/images/smilies/thumbs.gif
The last stage of flap is almost all drag with little contribution to CL (coefficient of lift) so he immediately got rid of some drag.
The go-around procedure on, e.g., the B747 is - max thrust, flap 20 (jus' like that!) and you don't drop out of the sky but transition instantly to a high energy situation partly by getting rid of drag which has permitted you to keep the engines spooled up just for that eventuality.

Come on, flaps reduction is fine when high and far from the runway as it requires a speed increase (nose down) loss of altitude. Anyway, the flaps reduction technique to increase distance has to be completed by flaps extension during the flare in order to benefit from final lift increase, ground effect and speed reduction to allow low speed/low vz impact.

Since the plane was under AP flying the glide, retracting the flaps definitely increased the AOA to compensate the loss of lift and accelerated the stall. To me, retracting the flaps at low speed/altitude while the AP is desperately trying to fly a path passing 50 ft over the threshold is a weird technique while the only thing that matters is to make the threshold. For sure, the glide is not the best path to the threshold, as retracting flaps doesn't help when you're plane is 14 degrees nose up with almost no power and the AP in charge.

[snanceki]

IMHO I can't help but think that we are still missing the point.

Accepting that sufficient evidence exists to point to fuel restriction I remain open minded regarding the cause.

For ice to have formed, to the extent required to restrict flow, a considerable amount of water would need to be present in the supply from the fuel tanks and in addition some mechanism would have to be present to make this situation common to both LH and RH systems.

Now the AAIB choose the word "accretion" I believe with considerable care. I suspect that used this word since it infers the presence of a "nucleation" site. It also indicates "growth".

So a mechanism has been proposed that ostensibly could be common LH to RH. However the conditions by which the growth takes place has not been indicated. i.e. Growth from passing ice crystals "aggregation" or "freezing" of dissolved water from solution.
Either way COULD explain why such a RELATIVELY small quantity of water caused the restriction since the restriction would build up over time.

IMHO I wonder whether the intuitive design practice to consideravly oversize fuel supply lines is in fact counter productive since this reduces fuel flow rates which ARE LIKELY to significantly accretion rate.

Add to this the fact that fuel economy is improving and thus reducing flow rates MAYBE we have reached the reached the edge of the envelope of our (lack of) understanding of permissible water content.

This might actually support why the AAIB actually only sited the Trent 800 and left the wider picture to other agencies.

Strikes me we are facing a design maturity / standards issue and that it is an issue of lack of understanding (technology maturity) rather than something specific being/having gone wrong.

Following this logic I would have have thought that some relatively simple experiments could be done to determine accretion rates at differing water concentrations, flow rates and temperatures, could be produced.

The difficult bit will be determining whether the subject aircraft meets these "new" requirements and then subsequently potentially all aircraft in operation.

[TheShadow]

snanceki said For ice to have formed, to the extent required to restrict flow, a considerable amount of water would need to be present in the supply from the fuel tanks and in addition some mechanism would have to be present to make this situation common to both LH and RH systems.

A small amount of water coming out of solution due to super-cold temperatures can form a sizeable ice-block if it all sinks to (or aggregates at) a common (left and right side) low point in the system. What could cause water to exit solution at a particular point (and later melt from its attachment point and migrate during the warming descent)? Perhaps it's a function of:
.
long-term exposure in the cruise to super-low temperature as compounded by.....
.
pressure drops at constrictive flow-points (such as in a venturi) and .....
.
a very cold area (not all areas outside the pressure hull stay at a homogenous temperature). Aerodynamic stagnation points can cause significant temperature variations, particularly where piping runs along or immediately adjacent to the aircraft's skin.
.

Reflect upon what water does in another fluid (i.e. air) when it's cold enough. It will form freezing rain (that hits and sticks and accumulates upon impact). It will also form snow and hail, depending upon relative humidity, the temperature strata (lapse-rates), condensation nuclei and the recirculation found in strong convective flows. Atmospheric water will form rough shapes upon wings and fuselage as clear or rime icing, particularly in areas where the airflow tends to be slowed or stagnates. The equivalent outcome within fuel tanks is dependent upon the thermal and fluid dynamics that are in internal play. If the fuel-feed obstruction was actually a coalescing mass of "not so small" ice particles (i.e. an icing "tumour" or growth), rather than a detaching mobile lump, we should not be amazed.

[pax2908]

I still find it annoying that "fuel temperature" is actually just one sensor, in a relatively big system. The explanation given in the report, why the measured temperature is representative, is quite short!

Someone mentioned that the FOHE is regulated. I don't remember this was mentioned in the report. Is it true? What other temperature probes are there to read out? Oil temperature maybe?

When did the "obstruction" start? I understand of course that by the time the FMV is fully open and the thrust is less than commanded, you can say the fuel flow is (already) restricted. But how about before this? When did the valve position start being inconsistent with the thrust demand?

[snanceki]

@ The Shadow.
I think you are reinforcing what I tried to say.
Yes, your analogy to a tumour is good.

I believe that this has been a "latent" problem for some time.
I believe that the key will be found to be low flow rates exacerbated by minimum use of thrust during descent, rather than unique temperature conditions.
Of course low sub zero (normal) fuel temps are a prerequisite.
I still believe that fuel distillation / composition may have a bearing on the issue by impacting the water solubility/temperature characteristics.

So I wonder where flow rates are at their lowest, away from potential energy sources and combined with profile changes that might act as a nucleation site.


I don't believe that the tumour broke away and blocked some downstream area. For this to have occurred at almost the same time in both independent systems is one step too far on the coincidence scale.

We'll have to wait and see.

[Basil]

DC8,
I intended my comments to be taken separately with the go-around as supporting comment.

sispanys ria,
You do not post your background in order for we experienced heavy jet pilots to accord appropriate weight to your comments. Please re-read what has been said about landing flap.
The accident took place eight months ago and here we are, in the cold light of day, following a good night's sleep, still discussing the actions of the flight crew who, following a long flight, had seconds to consider ways of ameliorating a very confusing situation. The aircraft landed within the airfield perimeter; no one was killed; rejoice!

[sydneymike]

I think that BA/Boeing/RR need to respond quickly. There seems to be a groundswell of (Albeit uninformed) public opinion developing that until the problems are clarified and resolved, better to avoid the 777. This was "explained" to me as follows: "If the chances of such a random event are remote, statistics dictate that it could happen again today. In the meantime, I prefer to fly 4 engined planes." Never mind that this is not PEK in winter.
The old adage that "Because they don't make em with 6" comes to mind?

You know, there is a kind of logic to this and the markrting gurus need to respond.

[sispanys ria]

You do not post your background in order for we experienced heavy jet pilots to accord appropriate weight to your comments.

As you are an experienced heavy jet pilot you should be able to read my words and understand their technical meaning without needing my CV.

I'm not discussing the crew actions. They are what they are but some lessons could be learned from these actions, should we have proper information. Unfortunately I could only find 2 sentences about these actions in this report following 9 months of investigations.

As you are an experienced heavy jet pilot please elaborate on how stalling an heavy jet 170 ft above the ground under AP and with retracting flaps is a skilled maneuver as to decide to let the AP try to follow a glide which is leading far beyond the runway threshold.

For the flaps, your heavy jet will certainly have less drag at 25 than 30, provided that you increase the speed (since your AP is following the glide slope). If you don't increase the speed to balance the loss of lift, you will need to increase the AOA and your nose up heavy jet will probably generate more induced drag than you could save with your 5 degrees flaps retraction. Anyway, in order to extend engine out landing distances, full flaps should be used for the final flare.

Do I need to be a NASA test pilot to expect you to consider my words ?

[NigelOnDraft]

For the flaps, your heavy jet will certainly have less drag at 25 than 30, provided that you increase the speed (since your AP is following the glide slope).Abolute B****ks :ugh:

NoD

[atakacs]

would it not be helpful and practical (and perhaps necessary) to introduce an immediate warning and annunciation of the discrepancy between the Actual EPR and the Commanded EPR as soon as the more normal 2-3 second lag becomes a clear discrepancy as at about second 154[95] (in figure 2), rather than requiring crew to observe the discrepancy and establish if it is “just” a glide slope, autothrottle or other issue – even more so by second 160[95] when both engines are rolling back.

My thoughts exactly !

Should be relatively simple to implement. Actually I would propose a BA038 EICAS message... :)

[DC-ATE]

sispanys ria -
Thank you for your supporting remarks regarding the flap issue. Not that I need it, but it's nice to know you're not alone!

Basil -
>>>....."discussing the actions of the flight crew who, following a long flight, had seconds to consider ways of ameliorating a very confusing situation. The aircraft landed within the airfield perimeter; no one was killed; rejoice!"

You are absolutely correct in that. That is NOT what I was attempting to prove/disprove, however. As -sispanys ria- wrote, we're trying to learn something here should another pilot/pilots ever be faced with a similar situation in the future. I stand by my remark that I think it was improper to raise the flaps at that point in time under the conditions that existed. BTW, I'm a retired DC-8 Captain. Not that that makes me any more qualified than many others here. But I DO know what it's like to have the flaps dumped on me! First thing that happens is.....you guessed it; airplane goes DOWN.

Now.....back to the report. I still question the preliminary findings about ice/fuel. Granted, I wasn't qualified on the 777, but I'd be interested to know about the fuel heat on board that machine. I was qualified on the 737 and we had to turn on the fuel heat manually; and did so often after observing the fuel temp gauge. Don't recall now the temp at which it was to be turned on, but it was something that was watched even though flight legs on that little bird were obviously much shorter than the flight in question.

The DC-8 had a fuel/oil heat exchanger that the crew had no control over and I've been in the air for 9 hours (KORD - PHNL) with no known problem.

Let's hope when the final report comes out we really know what happened so that it may never happen again.

[Desk Jockey]

I think that BA/Boeing/RR need to respond quickly. There seems to be a groundswell of (Albeit uninformed) public opinion developing that until the problems are clarified and resolved, better to avoid the 777. This was "explained" to me as follows: "If the chances of such a random event are remote, statistics dictate that it could happen again today. In the meantime, I prefer to fly 4 engined planes." Never mind that this is not PEK in winter.The old adage that "Because they don't make em with 6" comes to mind?

You know, there is a kind of logic to this and the markrting gurus need to respond.


I don't think It's usual for Airlines to comment while an investigation is ongoing unless it's in answer to media questions. In fact BA did answer questions soon after the event.
As far as technical action is concerned airlines and engineers don't wait for investigations to report before taking steps to try to prevent another event whether the incident is their own or another airline.
In this case fuel was such an obvious common denominator steps would have been taken to focus on fuel and fuel systems servicing and maintenance and repair and their operation by the crew.
Safety information is shared in the aviation community, no one would want airlines to compete on the basis of safety records because the two are not compatible.
It's what the travelling public would expect and it's what they get.
As far as marketing gurus are concerned airlines don't overtly market safety. Safety statistics are around if people want to look.

[barit1]

Brainstorming for a minute - only half-facetiously:

Inasmuch as fuel is the common link in BA038, 2 or 4 or 6 or 8 engines would be equally vulnerable.

The obvious answer is a dual-fueled engine - a few minutes' supply of hydrogen (or methane) under pressure would at least allow you to pick a better crash site.

:cool:

[sydneymike]

As far as marketing gurus are concerned airlines don't overtly market safety. Safety statistics are around if people want to look


I think you're missing my point, which is, I conceed probably off-topic and anecdotal. The fact is, however, and the commercial side of the industry does need to deal with this, there is a growing PERCEPTION (Which is not the same as technically proven fact) amongst the travelling public that the 777 is not safe and that 4 engined planes are safer.

Rationalize it as you will mate.

[md80fanatic]

A good start would be to -reduce- the presence of additives in jet fuel, some of which are designed to absorb water (dessicant). What was once a smattering of tiny manageable crystals of ice is quick becoming larger chunks that cannot always pass cleanly through the system.

[sooty655]

barit1 said

The obvious answer is a dual-fueled engine - a few minutes' supply of hydrogen (or methane) under pressure would at least allow you to pick a better crash site.



It would have to be a fuel storable as a liquid to get the package down to a reasonable size - maybe propane - and it would still require a large, heavy, high pressure bottle. Why does that remind me of the Qantas B744 depressurisation??

Maybe a simpler alternative would be to provide a second fuel feed pipe from tank to engine. At present, the engine's ability to "suck" fuel only protects against a boost pump failure - a dedicated pipe would protect against ANY fault in the normal supply system.

[Smilin_Ed]

When did the valve position start being inconsistent with the thrust demand?I think pax2908 has it right here. Following up on this would also prove, or disprove, snanceki's embracing of the accretion vs. break-off scenario. I agree with snanceki.

[grebllaw123d]

I think that I have read all the posts on this thread.

But I do not think that the following questions have been put forward - correct me if I am wrong!

Anybody knows the dimensions of the different fuel system pipes - especially the pipes coming from the wing tank booster pumps and terminates at the engine HP pump - the part of the fuel system where the AAIB suspects the blockage may have happened.

How many meters approx. and what is the diameter of the pipes?

I am just curious.

[overthewing]

A good start would be to -reduce- the presence of additives in jet fuel, some of which are designed to absorb water (dessicant). What was once a smattering of tiny manageable crystals of ice is quick becoming larger chunks that cannot always pass cleanly through the system.

I haven't seen this mentioned before, and didn't know that additives are water absorbers.

Having once overdosed a garden pot with water-retaining gel granules, I'm aware of how dramatically such materials can expand. (Looked like the patio had been attacked by flying jellyfish.) If the additives in fuel are in any way similar, is it plausible that they could form lumps large enough to cause problems?

If the fuel contained very little water, might this be a reason why?

Not a pro, ready to be put right...

[Rainboe]

3333333333333333333333

[esa-aardvark]

Dear Rainboe,
I think you fall into a great big hole in assuming that you
actually know what 95% of SLF think. Of course the majority
only want get from say Gatwick to Alicante, but of course
they can only travel on what is provided. In the same way that I can only vote for one or another party in a general election. So we rely on the authorities to make our travel
as safe as possible in whatever aircraft, and we expect them
all to be safe (whatever that means). For me, (Nowadays) I travel once or maybe twice a year northern to southern hemisphere and vice-versa, and short haul only to get to the long haul.

I always choose 747, not because I think it's safer, I do expect safety even in a 777, but I choose the 747 just because it is more comfy. So please don't dumb down people that you don't know, therein lies madness.

Kind regards ,John

[Swedish Steve]

Someone mentioned that the FOHE is regulated. I don't remember this was mentioned in the report. Is it true? What other temperature probes are there to read out? Oil temperature maybe?

The FOHE is not regulated. There are bypass valves in case of blockage, but no regulation. There is an Air cooled Oil cooler also in the system which is controlled by the FADEC to regulate the oil temp.

[chris weston]

md80fanatic 1836

Sir, I bow to and respect your expertise on the mad dog but the additives used to scavenge traces of water in jet fuels do not dessicate in the manner you suggest.

What was once a smattering of tiny manageable crystals of ice is quick becoming larger chunks that cannot always pass cleanly through the system.

The additives used are usually alcohol based derivatives of ethoxy ethane which use their OH groups to act as chemical bridges - using their OH groups, to Hydrogen Bond to the water molecules and simultaneously Van der Waals bond -with the rest of their structure, to the hydrocarbon fuel molecules.

Net effect of all this chemistry in action is to pull the water into solution in the fuel and not repeat not to accrete it into solid phase lumps.

http://en.wikipedia.org/wiki/Fuel_System_Icing_Inhibitor

Hope this helps.

CW

[Rightbase]

Green-dot, Swedish Steve:

There are so many unknowns. Not disagreeing, just thinking on....

For an arrival in approx freezing temperatures, my calculations suggest a worst case of 500ml of new atmospheric water in the CWT (from here (http://www.tis-gdv.de/tis_e/misc/klima.htm)) which, by the same mechanism we see under the main tanks, will mostly be ice on the coldest inner surfaces of the tank. When the tank is subsequently partially filled with slightly warmer fuel, some of this ice will melt and run into the fuel as suspended droplets. With the aircraft at rest, it is not clear how much of this will collect at the sumping point.

Unless it freezes again, once the aircraft comes alive the scavenge system will deal with whatever water the warm fuel melted. But the ice will remain, presumably to accumulate over successive flights?

I believe there are reports (sorry - can't find references at present) of water-in-fuel warnings at start up which sort themselves out during taxi. The scavenge works. What is interesting is the amount of water needed to trigger such a warning, which as I recall is quite a lot. Such reports suggest that after fuelling, sumping was either not done, not done properly, or the water was somewhere else when the sumping was done, and only collected at the lowest point after start-up.

Given the effectiveness of the scavenge systems, the only time I can see water collecting to be sumped would be when a large amount of accumulated ice has melted after shutdown. The big question is can ice accumulate in this way?

[M.Mouse]

I always choose 747, not because I think it's safer, I do expect safety even in a 777, but I choose the 747 just because it is more comfy.

You miss Rainboe's point though that the MAJORITY of people have not a clue what aeroplane they are flying in.

Most people are only interested in how cheap the air fare is!

[dxzh]

1. Possible interim safety measures suggested by Boeing

I could not find it expressly referred to elsewhere in this thread but interim safety measures as reported last week to be 'in the pipeline' were:

"Boeing's [Nick] West said the initial instructions will be to periodically vary altitude when fuel in the main tank is below minus 10 degrees Celsius, and to advance the throttle to maximum for 10 seconds before the final descent when fuel has been below that temperature for more than three hours, clearing out any water buildup.

The instructions cover 220 777s powered by Rolls-Royce Trent 800 engines in service with 11 airlines worldwide, Boeing said. For 777 aircraft on the ground in freezing conditions, fuel pumps must be run at maximum for one minute each to prevent water buildup, the planemaker said.

In the U.S., the FAA will send a directive within two days covering 56 777s operated by AMR Corp.'s American Airlines and Delta Air Lines Inc., agency spokeswoman Alison Duquette said. The carriers will have 10 days to comply, she said."

see http://www.bloomberg.com/apps/news?pid=20601102&sid=aJRdsqtHA6Kw&refer=uk (although seems to be mistaken reference to "frozen kerosene").


2. Earlier FAA leaked memo

The apparently leaked FAA memorandum dated 24 January 2008 disclosed back in February 2008 (see New BA 777 info - Airline Pilot Central Forums (http://www.airlinepilotforums.com/cargo/21805-new-ba-777-info.html)) seems to have been largely consistent with information only revealed in the latest AAIB interim report (eg see the fluctuating right hand engine P30 data). It seems that the reference in the memo to:

"• Ice in the fuel somehow limiting the fuel flow to the engines. A maintenance message indicating excessive water in the center tank was set during taxi on the two previous flight legs, although it cleared itself both times. The airplane was being operated in a high humidity, cold environment, conducive to ice formation."

was also correct in part - perhaps though the maintenance messages of excessive water must have been discounted for the time being by the AAIB (and therefore not mentioned in the interim report) as a result of the sumping on both 14 and 15 January 2008 - ie presumably prior to each of the two previous "flight legs" – which in revealing no excessive water allow any earlier excessive water messages to be set aside as erroneous or of no import? Would it be sensible to recommend that such a message is brought to the pilots' attention as an EICAS advisory message, given sump checks will not necessarily indicate for some time after an uplift of warm fuel into a cold centre tank what water may have been hidden away there as ice? Better to learn before the flight than after the flight when nothing that can do about it? What advice is there if a pilot searches out the relevant page in the course of a long cold flight and discovers such a message this week?


3. Any way for melted ice to go from centre tank to each fuel manifold, not via main tanks?

Given the possibility of centre tank ice from the volume of water implied by any excessive water message (ie potentially more than 627 litres – see http://www.pprune.org/3879461-post229.html - although in up to 79 tons of fuel) and the icing issues hinted at by the ongoing reporting requirements and proposed design changes in respect of the fuel scavenge pumps in related 777 series centre tanks (and for at least one operator apparently reported on 200ER), is there any other way in which ice from the centre tank might end up as a restriction in each feed line from the main tank without such ice causing water to be found at more than 40ppm in the main tanks themselves after the accident?

When the AAIB state (page 18) that "a low pressure in the fuel manifold would have led to air being drawn from the centre tank, via the jettison and override pump check valves", would this permit melted ice from the centre tank to pass directly to each fuel manifold (not via the main tanks)? If so, what would the pressure differential between each fuel manifold and the centre tank have to be to open the check valves? Is there a way for such differential to have occurred during the latter part of this flight and without a warning message, given the boost pumps were ON (implying it seems some positive pressure in each main tank feed line relative to the vented main tanks in the absence of any EICAS advisory of main tank FUEL PUMP low pressure) and the OJ pumps were OFF?


4. Icing scenarios

Icing even in the low flow scenarios outlined in the interim report certainly seems tricky to explain convincingly, unless the scenario also involves either:

- a lot more water in the flow available to accrete (taking into account back-to-back cold-soaked legs, centre tank unsumped water, etc) through the system, and/or

- an accretion "sweet spot" in each boost pump or a particular section of manifold common to each side of the system and no other spot to attract icing, so that the very low concentration of water in the slow fuel flow prior to its consumption by the engines can be sure to accumulate in sufficient volume to make the required restriction (and be dislodged as appropriate).

[Backoffice]

Just testing a thought here...wing tanks presumably will have an air gap over most of their enclosed surface near the end of a flight. Could a large flat sheet of condensation created ice have broken away, perhaps during the rapid descent to warmer air ?

[ACMS]

I agree, I'd say that over the years 80% of the people I've chatted to had no idea what type of Aircraft they flew on or how many engines it had.
Sad, but true.

[Old Fella]

Not only do few of the travelling public know what specific type they are flying in, they have no idea about those flying the thing. As long as the cabin is comfortable and the cabin crew helpful they are happy. Could be chimpanzee's flying the aircraft for all the pax care.

[sydneymike]

Rainboe:


Let's face an uncomfortable truth! 95% of the great travelling public have no idea what they are travelling on.


And the other 5% are most likely to be frequent business travellers. You know, those who sit at the front of the plane (Just behind your little office door) and pay your salary.

Fact is, the belief that 2 engines cannot fail simultaneously has been disproven.

[GEnxsux]

Fact is, the belief that 2 engines cannot fail simultaneously has been disproven.


The fact has never been that "2 engines cannot fail simultaneously". It has a very, very low chance of occurance (I think R-R uses 1e-09???), but certainly is not impossible.

[M.Mouse]

If we want to go down the road of pointless statements I believe that total engine failure has occurred on a B747 three times to date due volcanic ash. I do not believe that makes a four engine aeroplane intrinsically unsafe any more than an apparent fuel problem makes a B777 intrinsically unsafe.

[dxzh]

Here is some alternative speculation as to how a concentration of water in excess of 40ppm (ie in excess of water concentration found in main tanks) not derived from the main tanks might end up in each fuel manifold and thereby be a contributory factor to the suspected restriction in each feed line at late stage in flight:

1. Common cause - water in the centre tank after back to back long cold soaked sectors in humid conditions.

2. Otherwise normal operation - on return sector, any concentration of water in centre tank fuel transferred in first 2.5 hours by OJ pumps to each fuel manifold would not restrict the fuel lines (and would be consumed in the engines before it could become a contributory factor) due to the relative warmness of the centre tank fuel as compared to, say, the much faster plummeting temperature of the main tank fuel (which remains in the main tanks until about the time the OJ pumps are turned off) and the Critical Icing Temperature.

3. Common event - EITHER a concentration of water in remaining centre tank fuel at time switched off OJ pumps left a concentration of water beyond the OJ/jettison check valves in part of each fuel manifold connected to, but not subject to the cold slow flow from, the main tank feed, OR an event (relative low pressure in that part of each fuel manifold as compared to centre tank sufficient to overcome OJ/jettison check valves for a few seconds or more) after the OJ pumps were originally switched off leads to a concentration of water left behind in the otherwise empty centre tank flowing through the OJ/jettison check valves into the much colder mass of main tank fuel in each fuel manifold.


It is probable that water and/or ice may accumulate under certain normal certified operating conditions in the centre tank. However, given the circumstances of flights similar to BA038, arguably the bare results of general sump testing of the centre tank may be unrepresentative of the probability of this common cause becoming one of the contributory factors to this accident. For example, to what extent has sump testing been done in warm hangar or only several hours after uplift of warm fuel, in each case before further flight after the return from long back to back cold-soaked sectors in humid conditions? How much free water might be found in an empty centre tank but not come out of centre tank sump due to where it is located behind a baffle or at an alternate low point in centre tank (or it being frozen at the time, it not having been in a warm hangar)?

[pilot999]

i have to say with over 10000 hours pic. when I get on a bus, boat, taxi . I have no idea what i am in or on. or how many engines the boat has, :ok:

[Re-Heat]

I think you're missing my point, which is, I conceed probably off-topic and anecdotal. The fact is, however, and the commercial side of the industry does need to deal with this, there is a growing PERCEPTION (Which is not the same as technically proven fact) amongst the travelling public that the 777 is not safe and that 4 engined planes are safer.
What utter rubbish. Have you visited flyertalk, and perhaps seen that regular business travellers there have absolutely no qualms about stepping onto a 777 (and they do indeed know what aircraft they are boarding).

This is just melodrama. The incidence rate of the events encountered in this flight is so small as to be remote - as stated by the AAIB.

You clearly have little understanding of aircraft if you believe that a 4-engined aircraft would not be affected by similar common faults. Are we returning to posts from people who believe everything is dangerous if they do not fully understand it? I certainly hope not.

[Swedish Steve]

It is obvious to me that the centre tank contents is warmer than the wing tanks. The centre tank is emptied on every flight. The tank has packs under it, a warm cabin above it and a lukewarm freight hold in front of it. Even the wheel well behind it is warmer than ambient.
So why no save a few tons of fuel in the centre tank, and use it for the final descent and landing? All you have to do is turn off the centre tank pumps at say five tons remaining, and turn them back on at TOD. The higher delivery pressure of the OJ pumps would ensure the warm (how warm?) centre tank fuel is delivered to the engines, with reserve fuel in the wings to take over if necessary.

I believe there are reports (sorry - can't find references at present) of water-in-fuel warnings at start up which sort themselves out during taxi.
These warnings are not visible to the crew, but are stored in EICAS memory.

[Hotel Mode]

So why no save a few tons of fuel in the centre tank, and use it for the final descent and landing? All you have to do is turn off the centre tank pumps at say five tons remaining, and turn them back on at TOD.

For this particular incident maybe that would have worked. However running both or all 4 engines from a single tank from the same source would seem to be a negative step and against the design philosophy.

What happened is one of those accidents that aircraft designers/airlines rather than the pilots need to learn from, something that has been rare since the late 1970s.

[dxzh]

In summary, the holes in Swiss cheese (contributory factors) seem to me currently to be that within certified flight envelope:

1. Operational environment

- Long cold-soak sector.
- Back-to-back with another long cold-soak sector.
- Low fuel flow from main tanks at all stages of flight (never more than 30% or so of max certified flow).

2. Design

- Centre tank prone to accumulation of water and ice.
- Centre tank fuel scavenge which does not time-out.
- Introduction of centre tank water into very cold main tank fuel.
- Perhaps, areas such as suction feed prone to blockage by undissolved air.
- Fuel feed lines and/or FOHE prone to restriction by ice (whether accreted at site of blockage or not).


Swedish Steve, I agree but am guessing that the powers that be prefer not to keep much warmer centre tank fuel for landing:
- to ensure efficient wing loading in rest of flight;
- to make sure "independent" fuel supply to each engine in case supply to both is compromised on short finals (how unlikely is that!) not necessarily as a result of running out of fuel but perhaps using up dregs undiluted by main tank fuel and
- dependence on switching to main tanks close to landing (even automatically) and/or switching off OJ pumps (for TWA 800 reasons) is perceived to increase risk at time of potentially heavy workload?

[Backoffice]

At the risk of being a nuisance and, I’m sure this has been discussed before on this thread, but there could be an explanation for large amounts of condensation ice breaking off the roof of both wings simultaneously – vibration through the wing caused when either the landing flaps were extended or the gear went down.
The ice would not melt when falling into the fuel due to its temperature. When the pumps started sucking the ice was drawn to the filters.
i.e. The ice was nothing to do with water in the fuel which was loaded.

Just a thought.

[Poof in Boots]

In spite of many months of investigations and now the AAIB preliminary findings, talking to my Flight Crew colleagues on the 777, none of them seem to believe that ice was the problem.

VC10's in the 60's used to fly reglularly over 40,000 feet. There did not seem to be any problems with fuel icing in those days?

[grebllaw123d]

Poof in Boots,

"In spite of many months of investigations and now the AAIB preliminary findings, talking to my Flight Crew colleagues on the 777, none of them seem to believe that ice was the problem."

OK then: what DO your colleagues believe was the problem?

[BAe146s make me cry]

BA Engineering maintenance is under scrutiny at present due
to a variety of non-compliances raised in the form of reports
to CHIRP. The Engineering Director at CHIRP is incidentally
ex-BA. UKCAA SRG (Many ex-BA staff) have yet to comment.

On commercial aircraft, routine maintenance is performed daily.
The time intervals of daily routine maintenance cannot be deferred.
These tasks would include the draining of water from fuel tanks
IAW the Aircraft Maintenance Manual.

I would hope that attitudes to task completion have not altered significantly since I worked there. Documentation & certification of all tasks undertaken must be recorded. AAIB must ensure previous draining
of fuel tanks tasks for this A/C were actually completed (Not simply penned off).

BAe146??? :{:{:{

[Re-Heat]

BA Engineering maintenance is under scrutiny at present due
to a variety of non-compliances raised in the form of reports
to CHIRP. The Engineering Director at CHIRP is incidentally
ex-BA. UKCAA SRG (Many ex-BA staff) have yet to comment.
What exactly are you insinuating? There is not only no suggestion that this is the case, but this is extremely off-topic when the recent report has narrowed down the investigation to some very specfic areas. Further, the non-compliance to which you refer did not to my knowledge ever relate to tasks not being completed and later falsified, but instead to people of incorrect qualification working on tasks at Cardiff.

Judicious deletion of irrelevant posts from the moderator please?

[lomapaseo]

"In spite of many months of investigations and now the AAIB preliminary findings, talking to my Flight Crew colleagues on the 777, none of them seem to believe that ice was the problem."

OK then: what DO your colleagues believe was the problem?

Flight safety is not decided by poll taking.

Questions are natural as this thread has proven. However, when Service Bulletins are issued by the manufacturers and/or authorities they should be complied with.

When the pilot community have questions about the application of a SB that is the responsibilty of the issuer to defend.

Many questions remain and hopefully many will be answered in time. However as some are answered then solid recommendations will be issued.

[777fly]

Grebllaw123d:

In answer to your question, I suggest you read the whole thread again.There are plenty of alternative suggestions as to the cause....

[BAe146s make me cry]

RE-HEAT

Please step down from the box. This is a public forum and
as such, informed opinions from people in industry (or otherwise)
can and should be aired and shared.

There appear to be fundamental problems with how BA Engineering operates at present. This has been initiated by concerned BA maintenance
personnel.

Some of the best Licenced Aircraft Engineers remain at BA Engineering, however, not many as so many have chosen to leave. In closing,
the compliance or deviation of/from AMM practices & company SOPs within BA Engineering, early 2008 shall always be relevant to the
loss of this B777...

BAe146??? :{:{:{

[CargoFlyer11]

I don't have any technical knowledge like other who have posted here, however, I've been flying transport jets myself since 1978, current wide body captain, and I've never heard of fuel icing of this nature. Certainly, in most cases, such an occurrence would not be a one time thing, considering how many hours are flown each day by different types of aircraft exposed to different cruise altitudes temps and fuel loading conditions; if anyone has any knowledge of a previous occurrence, that might add some credence to this scenario....:bored:

[Bobbsy]

SLF here. I've avoided any comment until now because I have no knowledge to add to the topic.

However, one thing I can say is that my faith in the 777 is in no way dented and I happily fly that plane. One isolated incident does not a pattern make.

Bob

[Poof in Boots]

One theory being propogated is that the incident was more to do with the software....ie: the lines of software code.

Perhaps on the BA038, glitches buried somewhere in all those lines of software code came together like holes in a cheese......

[Shaka Zulu]

dear PinB,

I am one of your 777 Flight Crew and as such used to believe that it might be an EEC software error however the NEW AAIB report clearly narrows the possible cause down to one specific area.
Software errors always happen, on any plane so it would have been plausible.
The AAIB wouldn't have written this report without proving that another error would have been a better fit for what has happened.

Fact of the matter is we don't know how ice behaves at high altitude at extreme low temperatus in a complex mix of JetA1.
Certainly in my mind we can put the software glitch to bed.

[DozyWannabe]

PinB:

Head back to post #1661 and you'll find a series of posts from one of the guys who worked on the RR FADEC system. The whole discussion was pretty much encapsulated there.

[scrivenger]

'Fact of the matter is we don't know how ice behaves at high altitude at extreme low temperatus in a complex mix of JetA1.'


I find this statement, if true, to be extremely worrying. I mean haven't we been flying for many, many years with JetA1 at high altitude and extremely low temperatures or am I missing something?

[Oilandgasman]

Some of the physics of water in Jet A1 at www.facetinternational.net/pdfs/aviation/aircraft_refueling.pdf (http://www.facetinternational.net/pdfs/aviation/aircraft_refueling.pdf) It would appear that the behaviour of water as the fuel temperature falls is understood.
Back at the AAIB report graph on page 5. (bottom rt hand corner, enlarge to 800% for a clear view) Does anyone understand why the fuel consumption from the left hand main tank increased immediately after the scavenge from the centre tank. This following 7 hours when the fuel consumption from both tanks was identical?

[tanimbar]

It is true that the AAIB report that 'little is known' about ice crystals in fuel at temperatures below 18C (0F) - see my post 1725,page 87.

Its worse because the AAIB don't mention the overall operating environment, just temperature and not pressure, vibration, fluid circulation etc..

This is not meant to imply any wrongdoing on the part of the AAIB. Actually, I suspect that if you were to have a private conversation with the AAIB report writers the air would turn blue if you asked them to describe the industry's fuel standards. I wonder when the AAIB realised that 'the standard' has a huge whole in it.

But, has the industry simply lost or forgotten the knowledge that may have been gained from tests/experiments etc. conducted decades ago?

Some older crew have already posted here .... can anyone shed light on fuel tests back in the '50s and '60s that lead to the development of the fuel standards?

Regards, Tanimbar

[tanimbar]

Thanks for the link to the PDF from Clarcor. Just read it and it doesn't help us understand the behaviour of water in fuel as the temperature drops, other than in a general way.

Clarcor, as you know, make fuel filters and systems for ground based operations - storage of, transport of and re-fueling of aircraft. Fascinating to read that Fuller's Earth is still used as surfactant. Now that is an example of modern technology using knowledge gained centuries ago.

The discussion on microbes in tanks was interesting too.

Regards, Tanimbar

[Oilandgasman]

Tanimbar
The section I thought may be relevant concerns precipition of absorbed water from Jet A1 as the temp falls. This precipited water will form droplets then sink to the bottom of the tank. SG of Jet A1 0.78-0.80. Ice 0.9-0.95? In the case in point this precipited water will be in the form of ice crystals. Note your comments on microbes. If tanks are not treated with biocide during cleaning then they are another matter, will be present if water present, but are easily identified under the microscope. This must have been checked post incident as they are a well documented contaminant as are fungal spores.
The bottom line is that in the first sentence of ASTM spec for Jet A1, includes the phrase " bright, clear, and FREE from water". Not drops, not ppm, not entrained...none. If this is not what is being delivered on every occasion then there is a quality control issue.

[CONF iture]

dxzh
Do you give any credit to what you call that apparently FAA leaked memo (http://www.airlinepilotforums.com/cargo/21805-new-ba-777-info.html)

Therefore what do you think of the AAIB reports which do not mention:
- A maintenance message indicating excessive water in the center tank set during taxi on the two previous flight legs
- An auxiliary power unit (APU) auto start sequence
- A crossfeed valve opening

M.Mouse
As you correctly mentionned the fuel on board and the flap retraction before the AAIB did confirm your words, would you like to comment on that apprently FAA leaked memo ?

[dxzh]

CONF iture,

I am certainly now prepared to give more credence to the "apparently leaked" FAA memo dated 24 January 2008 (which popped up on the internet by 1 February 2008). This is because the purported inside knowledge in the memo of what seemed to be non-public, pertinent information at that stage of the investigation has been subsequently corroborated in many varied respects by information in the AAIB's later bulletins and reports. Was the memo as leaked only a draft (or even a forgery) I do not know - however, I try to note well the cautionary words drummed into us by PPRuNe about not taking everything at face value and hence I wrote "apparently". The memo itself ends with the words "Information only. This information is preliminary and is subject to change". If very curious about the memo's provenance, maybe the answer is for some brave soul to pick up the phone to its supposed author, Doug Pegors, and ask him - his direct line at the FAA is publicly available.

As regards the AAIB reports to date, I believe they are concise and well-written, concentrating correctly on the contributory factors to the underlying accident, rather than the consequent events as the aircraft impacted the ground. Actions at the time of impact may not be wholly irrelevant in so far as they may reflect on the status and set-up of the aircraft on or prior to the underlying accident. However, the key concern here is to understand the unheard of rollback of each of two seemingly fully-functioning engines at a critical stage of flight. I am not surprised that the AAIB's clear focus is on understanding the duplicated rollback and how to avoid a double failure condition in the future.

There are clearly gigabytes (let alone pages) of raw data and analysis which could be made public but that would be a disclosure exercise of an altogether different quality and for a very different purpose - this investigation is not the subject of some hugely expensive public enquiry or court case (thank goodness) and, as ever, safety in aviation has generally benefitted from measured disclosure of facts concentrating on solutions and not scapegoats and thereby encouraged full and frank offline discussions with accident investigators (rather than a**e covering for fear of litigation and a blame culture). The AAIB has already disclosed much more than it might have, but given the degree of rumours and speculation perhaps a balance has had to be struck.

Am I surprised or concerned that I have not received a download of all the data in the QAR, FDR and NVM or test rig papers etc? No. Am I surprised or concerned that the AAIB may omit from the 21 page interim report certain information about events which I assume the AAIB is confident happened on or about impact (perhaps technically part of flight until aircraft stationary, perhaps interesting to a pilot, but not relevant to the focus of the investigation)? No. Am I concerned that information in earlier AAIB bulletins such as about FOD (eg plastic scraper) has not made it into the interim report? No. In fact I really believe the AAIB is doing a great job synthesising the information and keeping the correct focus on the critical failure condition.

Nevertheless, I do speculate about the uncorroborated centre tank messages even though I can understand why if they did exist the AAIB might have discounted their evidential importance given the sumping and, perhaps, a suspicion that the message is not as reliable as it might be and it would consequently be misleading to draw from it a conclusion that there really was 600+ litres of free water in the centre tank! On the point of water in the centre tank (as opposed to the omission of messages (if there were any, I stress) from the interim report), I feel a little rebellious as water in any tank bears on the underlying accident, even without any suggestion of such a message, and to my mind there is circumstantial evidence in the design and track record of 777 centre tanks suggesting a tendency to accrue ice and free water there. There is even in the (apparently leaked) FAA memo a second statement of information learnt on 22 January 2008 that "There was a message of water in the center fuel tank shortly after departure from Beijing." - ie implying that not just on the two previous legs, as learnt on 24 January 2008, but on the actual accident flight there might have been some ice which melted into free water in the centre tank. I could envisage a scenario along the lines of: existing ice already in the centre tank is gradually melted following the uplift of warm RP-3 fuel; the resulting free water triggers a message; and sufficient free water is then dissolved back into the bulk of the fuel by the water scavenge pumps' operation to clear the message.

As to the APU start sequence (around termination of QAR recording) and cross feed valve, I am very curious and have lots of questions and ideas, but I personally see little relevance to the real focus of the investigation even assuming as I do what is stated in that apparent FAA memo is not complete fiction - to the extent either were involved in events after the dual rollback process had started, I strongly suspect that the AAIB would see them as playing a secondary role and the data bears out that there was a much bigger issue already playing out - namely a critical restriction in both fuel lines.

[Fargoo]

BAe146s make me cry

BA Engineering maintenance is under scrutiny at present due
to a variety of non-compliances raised in the form of reports
to CHIRP. The Engineering Director at CHIRP is incidentally
ex-BA. UKCAA SRG (Many ex-BA staff) have yet to comment.

On commercial aircraft, routine maintenance is performed daily.
The time intervals of daily routine maintenance cannot be deferred.
These tasks would include the draining of water from fuel tanks
IAW the Aircraft Maintenance Manual.

I would hope that attitudes to task completion have not altered significantly since I worked there. Documentation & certification of all tasks undertaken must be recorded. AAIB must ensure previous draining
of fuel tanks tasks for this A/C were actually completed (Not simply penned off).

There appear to be fundamental problems with how BA Engineering operates at present. This has been initiated by concerned BA maintenance
personnel.

Some of the best Licenced Aircraft Engineers remain at BA Engineering, however, not many as so many have chosen to leave. In closing,
the compliance or deviation of/from AMM practices & company SOPs within BA Engineering, early 2008 shall always be relevant to the
loss of this B777...

I respectfully request you wind your neck in and start a fresh thread in the Engineering section of these forums if you have an axe to grind.

I'm not sure what your agenda is here but it's clear that the AAIB do not feel BAs Engineering or Flight Crew were the cause of this accident. I'm further confused by you're insinuation that BA Engineers deviatied from the AMM with regards to this aircraft. Also for you to even suggest that this task was "penned off" is a terrible accusation from a fellow member of the engineering community founded on not a shred of evidence.

These may be talking points and forums for discussion but you really need to be careful when slinging mud in a direction it is not deserved. :=

[BWBriscoe]

Have any measures been put in place operationally following the report?

[sispanys ria]

Am I surprised or concerned that I have not received a download of all the data in the QAR, FDR and NVM or test rig papers etc? No. Am I surprised or concerned that the AAIB may omit from the 21 page interim report certain information about events which I assume the AAIB is confident happened on or about impact (perhaps technically part of flight until aircraft stationary, perhaps interesting to a pilot, but not relevant to the focus of the investigation)? No. Am I concerned that information in earlier AAIB bulletins such as about FOD (eg plastic scraper) has not made it into the interim report? No. In fact I really believe the AAIB is doing a great job synthesising the information and keeping the correct focus on the critical failure condition.And do you believe in Santa Claus ? The reason why many countries are usually disclosing the raw recorded information is to avoid the investigations to be questioned. I'm glad you believe whatever is submitted to you but what will happen if (God forbid!) one day the AAIB is releasing inaccurate info ?

When I read this report and know that the crew got rewarded as heroes I really have the feeling of a bad joke. They certainly did save the day by finally reducing the AOA when the aircraft was stalling, but that's what any pilot is supposed to do as a very basic reflex. As a result I don't see heroes but only pilots who were probably surprised after a long flight and who did their best according to their perception of the situation. But no heroic behavior (at least not in what the report is stating about retracting flaps under AP and low energy conditions and aiming 300 m beyond the threshold...). Even with fully disclosed raw information many investigation autorities did already manage to release BS, what would make the AAIB so different ?
I recommend you to read the concord report, you would then understand how easy it is to use the raw data to realize the investigators are sometimes having very curious interpretations... Welcome to neverland.

[TheShadow]

My reading of the highlights from the initial FAA Report (http://www.airlinepilotforums.com/cargo/21805-new-ba-777-info.html) on Flt BA038 (below) is that:

a. There were center-tank water warnings on the previous two flights - as well as on the accident flight ex Beijing.

b. These were not unusual events and usually gave rise to a routine "sumping" to clear any collected water within range of the low-point drains.

c. Water warnings usually indicated (by design) a significant amount of water in the tanks.

d. Because the nature of the warnings were usually that they would appear and then self-clear, the 777's system had gained a reputation of intermittency and fallibility. It was generally believed to be flaky, unreliable and therefore no great cause for concern - beyond generating a requirement for a sumping post-flight.

However what may have been the case was that water in the fuel was circulating (courtesy of pumping and refueling) alternately into and then away from areas covered by the water warning sensors. Additionally (and frequently) the water would also (either) become dissolved in the fuel or freeze in non-designed water-trap areas and no longer be detectable as water. This would explain the (perhaps undeserved) reputation of the water detecting system as being unreliable and inconsistent. The attitude adopted by engineers would have been to respond to reported/recorded "water in tank" warnings by simply sumping (draining) from tank low-points at the next turnaround servicing. Self-evidently this would be totally ineffective if done soon after a long-haul high-level leg (water still frozen) OR soon after refueling (water redistributed by the refueling operation to areas well away from tank low-point sumping drain-valves - as well as being to some extent re-dissolved hygroscopically in the swirling warmer fresh fuel. It should be noted that water-detection IS traditionally done soon after refueling - and that may not be any longer such a good idea. Because the Beijing overnight was in sub-zero conditions, sumping would've been quite unproductive, even though fuel would have deceptively emerged quite water-free from the drain-points. At Heathrow, after the accident, the center-tank was ruptured (see FAA report below) and all the residual fuel was lost - including, it's presumed, any/all water evidence. Without clear data, the UKAAIB's bottom line would necessarily have to be quite conjectural. Boeing wouldn't abide by (and would vigorously contest) any proposal to redesign tanks, pumps, piping, filters and water-traps. The bottom line is most likely to be a greater constraint upon TAT's at which the 777 can operate. Longer legs in low outside temps will be flown at lower, less economic, altitudes.

The highest hazard area during a "latent" (dormant) water-carrying flight would be precisely as in the BA038 scenario, i.e. the center-tank fuel level is low and the water melting during descent and the detached lumps of ice moving towards engine-feed pump inlet ports courtesy of pump-suction, higher engine fuel demands (spool up during aircraft attitude changes - both on descent and on finals when configuring with gear and flap).

One further thought. How will the formula for fuel absorption of water change once tanks are nitrogen inerted? Will it be a catalyst effect (i.e. dissolved water being more prone to precipitate out and collect and freeze at low points) - or will there be a positive effect? Would it be possible to capture the (presently wasted) oxygen by-product of the NEA process and utilize it for fuel-warming? My guess is that the result of BA038's accident will be a token SOP change, a limitation on cruising at low ambient temperatures and an overall inconclusive and unsatisfying bottom line.

[philipat]

I do have very great faith in the AAIB. Together with the support from FAA and Boeing, it is difficult to imagine more expertise being available for an investigation. So I do believe that the iceing scenario is accurate and correct. It does just somehow continue to bother me, however :

Why has this never happened before during millions of longhaul flights in very cold conditions. Yes I know that there is always a first time for the holes in the Swiss cheese to align, but it still seems somehow improbable, logically speaking. Is the design of the RR Trent and FF so different from earlier designs and from GE/Pratt kit?
Repeat question to the 777 experts. Have the earlier incidents of failure to deliver commanded thrust been adequately explained?

[sispanys ria]

I do have very great faith in the AAIB. Together with the support from FAA and Boeing, it is difficult to imagine more expertise being available for an investigation. So I do believe that the iceing scenario is accurate and correct. It does just somehow continue to bother me, however :
Why has this never happened before during millions of longhaul flights in very cold conditions. Yes I know that there is always a first time for the holes in the Swiss cheese to align, but it still seems somehow improbable, logically speaking. Is the design of the RR Trent and FF so different from earlier designs and from GE/Pratt kit?
Repeat question to the 777 experts. Have the earlier incidents of failure to deliver commanded thrust been adequately explained?Faith has nothing to do with aviation matters. In aviation you know or you don't know. Saying you believe is meaning less. You should ask yourself why when concorde had dozens of incidents similar to the one which caused the fatal accident nobody moved. The NTSB made extremely precise recommendations in the 80s which were not considered by none of the manufacturer, the registery states, the operators, the investigation boards (including the AAIB). What faith are you talking about ?

[vapilot2004]

Repeat question to the 777 experts. Have the earlier incidents of failure to deliver commanded thrust been adequately explained?

As far as I know, the one-engine rollbacks have been attributed to software in the EEC and have not re-occurred since the updates were changed.

[Contacttower]

What faith are you talking about ?It's called reputation; the AAIB has over the years produced many reports of very high quality which have changed and improved the way planes are made and the way we fly. They deserve our trust.

[BAe146s make me cry]

Fargoo

No axe & no agenda. Your employer, our NAA & CHIRP have issues
that are likely to have contributed to this incident, a culture if you will - Too Cozy?

That same culture has possibly led you to believe specific tasks are
never 'penned off' in Base or on the Line - I certainly do not approve of the practice BUT it happens. Everywhere I have worked (including BA), despite ALL airworthiness requirements and HF rhetoric 2008, it still happens as no a/c engineer is immune to commercial pressure. There
is also the issue of BA supervision of techs/mechs, line & base. However,
this is not the place to digress.

As a fellow a/c engineer, I hope for nothing more than a full answer from the AAIB for this incident to prevent re-occurence :. I shall return to the Engineering Section as requested. For now.

BAe146??? :{:{:{

[sispanys ria]

It's called reputation; the AAIB has over the years produced many reports of very high quality which have changed and improved the way planes are made and the way we fly. They deserve our trust.

Once again, trust doesn't have anything to do with investigations. We are talking about facts. Investigations' raw info is to be publicly available to ensure transparency.
What kind of reputation do you refer to when considering none of your "high quality" reports has been released following the dozens of concorde's tires accidents, especially when this is seriously recommended by the NTSB ? As far as I know, one's reputation is presumed good until it's no more...

[philipat]

It's called reputation; the AAIB has over the years produced many reports of very high quality which have changed and improved the way planes are made and the way we fly. They deserve our trust


Apologies for poorly selected language, but that is exactly what I meant to say.

[L337]

As you correctly mentionned the fuel on board and the flap retraction before the AAIB did confirm your words, would you like to comment on that apprently FAA leaked memo ?

It is perhaps worth saying that allot of information has been made available to BA aircrew. Some of that information, such as the flap retraction, made it to pprune.

It interesting that despite BA having some 3000 pilots, very little "inside" information has made it to this forum.

[wilyflier]

Please may I remind The Shadow ,(his middle big paragraph), that the fuel uplift was NOT warm. I recollect a post stating it to have been minus 10 degrees C

[TheShadow]

But it may well have been "warmer" - as the post says......

Warmer stirred fuel added via refuel would tend to "soak up" ice-melt inside the tanks and perhaps invalidate any sumping.

[HarryMann]

It should be noted that water-detection IS traditionally done soon after refueling - and that may not be any longer such a good idea.

This crossed my mind too...

[dxzh]

And do you believe in Santa Claus ? The reason why many countries are usually disclosing the raw recorded information is to avoid the investigations to be questioned. I'm glad you believe whatever is submitted to you but what will happen if (God forbid!) one day the AAIB is releasing inaccurate info ?

When I read this report and know that the crew got rewarded as heroes I really have the feeling of a bad joke. They certainly did save the day by finally reducing the AOA when the aircraft was stalling, but that's what any pilot is supposed to do as a very basic reflex. As a result I don't see heroes but only pilots who were probably surprised after a long flight and who did their best according to their perception of the situation. But no heroic behavior (at least not in what the report is stating about retracting flaps under AP and low energy conditions and aiming 300 m beyond the threshold...). Even with fully disclosed raw information many investigation autorities did already manage to release BS, what would make the AAIB so different ?
I recommend you to read the concord report, you would then understand how easy it is to use the raw data to realize the investigators are sometimes having very curious interpretations... Welcome to neverland.
sispanys ria

Thank you for your message. In response:

- I do not believe in Santa Claus.
- "many countries" do not have the expertise to analyse the raw data, hence they may release the information to professional bodies such as AAIB or NTSB for evaluation - I believe we are fortunate to have the likes of the AAIB and the NTSB.
- I have tried to make clear that I do not believe everything, hence my evident scepticism about the apparent FAA memo, particularly initially - I try to have an open mind, even about other posters on this forum who can appear less dispassionate but nonetheless are only expressing their own genuine belief or suspicion.
- I am more concerned with the information already released and how accurate that is, since my interest is the conundrum which is the double failure condition demonstrated a minute out from landing at LHR, rather than events however interesting occurring afterwards.

- as regards your second paragraph, I have no doubt you read the report and, judging from your previous posts on this and the "BA crew gets medal" thread, you are upset that the AAIB has not published and commented more on the crew's actions - indeed, I cringe on your behalf at some of the hard (verbal) knocks you have taken.
- I believe you are mistaken in conflating your comment about "rewarded as heroes" with the AAIB, though given your belief I can understand why you are so passionate about challenging the apparent status quo.
- I appreciate your comment that the pilots "certainly did save the day", and perhaps in the maelstrom of attention after the event that was the media message, however clumsily stage-managed, that BA were trying to put across - and which the media unsurprisingly hyped as heroics.
- I note your continued challenge of the pilots' behaviour as deserving of a "heroic" standard. My gut view is that in a media age in the UK where people in the news tend to be characterised as either a hero or a villain (with no nuanced or neutral position in between), I can understand why BA, in supporting its brand and its crew, steered the story in the media towards the "hero" characterisation (by awarding a medal), even though I would be more inclined to express it in this forum as you did that they "certainly saved the day".
- I note your comments about flaps, AP and aiming point and, while I would not dismiss them, I am glad that the AAIB is concentrating on the primary issue here which is the double failure condition.
- I have few comments on this secondary issue of the impact other than to say with low energy, gear down, turbulence and a crosswind, I agree that the crew's actions saved the day by making a more than sufficiently controlled landing such that the hull survived and everyone walked away (or hobbled in the case of the person with a broken leg). I repeat that in my view to have a result like that in the circumstances they did a great job. It will not be possible to show that any other combination for landing would result with 100% certainty in an "as successful" non-fatal landing so, as a critique of the BA pilots' behaviour on the day, trying to show a better way of handling the aircraft is futile and risks becoming a mud-slinging exercise to be picked up by the media and against which the pilots concerned would have no ability to defend (not nice, and I assume why your genuine comments have at times been treated dismissively (also not nice)). That is not to say that you are right or wrong or that another thread on low, slow, heavy commercial jet, engine out landings would not be well read or of real interest.
- I note your lack of faith in other investigative authorities but see it as having no bearing on the professionalism and internationally recognised expertise of the AAIB, and the practical point that it is working hand in hand with the NTSB, Boeing and others.
- I have read the English version of the Concorde report previously. I would highlight to you that for many the key point coming out of the report was the analysis of the chain of contributory factors leading to the fire, rather than the way in which the crew thereafter tried to keep the aircraft airborne prior to it impacting the ground. The same point applies to the priority in this investigation.
- I have not assumed that investigators cannot get it wrong and I too will feel free to question their opinions if I believe I have the time and an important enough reason to do so - I repeat though that I genuinely believe that the AAIB have had the right focus and the crew did a fantastic job, saving the day.
- thank you for welcoming me to Neverland, but I think you have the wrong person - may I also take it you are not Michael Jackson incognito?

[dxzh]

Please may I remind The Shadow ,(his middle big paragraph), that the fuel uplift was NOT warm. I recollect a post stating it to have been minus 10 degrees C

The interim report states that the No.3 Jet Fuel uplifted was at +5C (see page 10 of interim report).

The centre tank was empty prior to the uplift, save for any ice which, especially if in contact with the uplifted fuel, might slowly melt but presumably without reducing materially the bulk of the centre tank fuel's temperature below +5C.

The main tanks still each contained 4 tons or so of fuel (seemingly from Figure 1 of report at -20C at least in left hand main tank). After the uplift of another 25 tons or so of fuel into each main tank at +5C, the left hand main tank temperature was never higher than -1C, hence it seems the main tank fuel temperature remained below water freezing temperature during, and for last two sectors (at least shortly after leaving LHR) either side of, turnaround in Beijing.

[Rainboe]

zzzzzzzzzzzzzzzzzzzzzzz

[Yellow Shark]

Investigations' raw info is to be publicly available to ensure transparency.


So what format do you think the FDR data comes in?

[dxzh]

Rainboe, I am beware but no good at the fire and brimstone. As I was "engaged", I just wanted to respond in a hopefully constructive fashion. My view is simple:

- the crew did a great job, together saving the day, getting the plane safely on the ground; and

- the expertise of the AAIB is correctly focussed on the contributory factors to what was a potentially catastrophic double rollback.

[suninmyeyes]

I totally agree with Rainboe. Two 777 training Captains who recreated it in the sim with the data available, ZFW, fuel, Flap 30 Vref (constant wind used as cannot simulate gusting winds) noted that from "Hang on, what's going on here" to hitting the grass was just 25 seconds. Once they had come to a stop just short of 27L there was a stunned sense of disbelief. Now bear in mind this was just a simulator, no life endangerment, and these pilots were expecting it. As soon as the power comes off the nose immediately pitches up rapidly to maintain the glideslope.Speed comes back to about 105 knots. Lowering the nose towards the horizon to regain lost speed results in an immediate descent rate of about 2,800 fpm. Not much fun in a widebodied jet at 500 feet with full flap. I would hate to think of the rate of descent if you lowered it below the horizon. I am amazed at the number of things different people on this forum have said the 038 pilots should have done in those 25 seconds. The pilots never claimed to be heroes.

Incidentally a lot of professional pilots do not disclose inside knowledge on this forum because the non qualified theorists like to challenge it, or correct it which is irritating to professionals. A little knowledge is a dangerous thing. Airlines are very safe but leaking information outside the industry can give the wrong impression. An example of this is MEL items and the outrage it created on the Spanair thread. Or an example outside aviation: You try telling someone who has never been in a car that during rush hour these things that weigh 1500 kgs go onto roundabouts at 30mph and miss other cars by only 3 seconds, or drive down motorways sometimes with separation times of only 2 seconds and you have blindspots where the driver cannot see cars behind him. There would be uproar, non-drivers on car rumour forums would say passengers should at all times observe the blind spot and warn the driver and all speed limits should be reduced by 50% to enhance safety. Flying is very safe. Leave it to the professionals.

[NigelOnDraft]

suninmyeyes - excellent post, especially the second para about us not saying half of what really goes on, since we just then get attacked by all the MS FSim experts :ugh:

NoD

[wiggy]

suninmyeyes...second paragraph,,:ok: sadly it will be lost in the noise

[remarkablebean]

suninmyeyes - you've just written my retort for the next wanton comment I get...which may well be tomorrow night at work:}
Good stuff:ok:

Sorry I can't afford the ghost writing fees.

In the meantime, can those who don't have a clue just be thankful Messrs Burkhill and Coward did.

[Roseland]

Is it a fact that the port wing probe is at the coldest point in the fuel's route from tank to engine?

If the pipework - for example in the pylons - could be colder, then any tests based on bulk fuel temperature would be optimistic.

[BlueRay]

bae146 is clearly stating that at british airways the water sump checks were never carried out, just stamped as being done. I recall earlier in this post baengineering saying the same thing! Clearly water was building up in this centre tank from poor maintenance practice that was widespread at cc.

All i can say is the sooner the media gets this out to the wider public the better. Also why has ba lied in the report? Making out they were doing a study on water sumping just before the incident! It would be amusing if the gravity of the situation were not so significant. A large aircraft nearly down over london.

Any other ba engineers wish to comment?

[sispanys ria]

I flew 747s for 18 years- you would not get me throwing the nose down at all!

And here is what is written in the AAIB report:

The stick shaker activated at approximately 170 ft, and shortly afterwards the First Officer made a nose down pitch control input which reduced the aircraft pitch attitude and caused the auto pilot to disconnect.

Probably that the FO didn't have 18 years of 747 behind him... but to me THIS is how he saved the day...

To dxzh:

Thank you for your gentleman's post. I really appreciated your comments and your open minded point of view. I'm sorry not to elaborate more on it as it is bedtime but you made your way to convince me. :ok:

[Jumbo Driver]

Well said Rainboe! Similar to you, I have some 23 years' experience on wide-bodies and nearly 30 years on four-engine jet transports and I can see a massive contrast between the opinions from the informed professionals and that of some of the inexperienced wannabees. I have been lurking for most of this thread, just amazed at some of the uninformed rubbish that has been posted - suninmyeyes, you are spot on with your recent post.

dxzh has some very sensible and constructive ideas to put forward - especially the recent response to sispanys ria, which was excellent reading - and suninmyeyes' subsequent comment says it just the way it is.

On the subject of the recent AAIB Interim Report, I congratulate them on a detailed and comprehensive update on the progress of the investigation. I, for one, have total confidence in their competence as an investigative body.

Now, back to lurking on this thread ...


JD
:)

[Rainboe]

33333333333333333333

[philipat]

BlueRay:


bae146 is clearly stating that at british airways the water sump checks were never carried out, just stamped as being done. I recall earlier in this post baengineering saying the same thing! Clearly water was building up in this centre tank from poor maintenance practice that was widespread at cc.

All I can say is the sooner the media gets this out to the wider public the better. Also why has ba lied in the report? Making out they were doing a study on water sumping just before the incident! It would be amusing if the gravity of the situation were not so significant. A large aircraft nearly down over london.




This misinformation is based on earlier misinformation and provides a good example of why many professionals will no longer contribute.

Firstly, the posts you are referencing did not refer to specific procedures which had been signed-off without implementation. Secondly, they were clearly from someone with an axe to grind, probably a disaffected (Ex?) employee.

I suggest that before you start reaching such conclusions you read the entire thread. This would give a much broader understanding and would allow you to judge the quality and credibility of individual posts within the bigger picture.

[sispanys ria]

These big jets are not like gliders with instant flap in 1/2 second. The only answer in a giant jet is to hold attitude and desperately hope you will retain enough elevator control authority to stop the nose eventually dropping as the speed falls and you lose your elevatorsDear, I think I sent you enough PMs to tell you that nobody here recommended to push the nose down. But since you only listen to experienced people, I understand my words didn't reach your brain. What you are now saying is EXACTLY what I told you in my PM: holding attitude (also meaning AOA and speed). Unfortunately the crew didn't have an opportunity to understand the situation before they loose too much of speed and the consequence is that they left the AP until stick shaker...
I'm sure you are experienced enough to understand that letting the AP following the GS is exactly the contrary of what you recommend: the AP didnt' hold the attitude but increased it up to 14 degrees nose up.

instant flaps- they could take 20 seconds whilst sucking your elevator control dry of all power!Once again I agree... while this is what was done... and that it contributed to increase the attitude to follow the GS (what you do not recommend as an experienced heavy jet pilot).

That is why I am brutal with this bitching by sispanys ria. He thinks he is an expert because he taught engine out in a little single engine fighter with no control problems. Sadly your 18 years experience didn't taught you how to hold control over your words. You should read dxzh's post, you would learn a lot on how to share a different point of view.


Stick the nose down, and it may be the last thing you ever do.This is exactly what the FO did at 170 ft... Please note that this nose down input is the consequence of letting the AP increase the attitude till stall...

Basically they did all the contrary of what you recommend (as an experienced heavy jet professional) :

They didn't hold the attitude
They did retract the flaps
They made a nose down input at low speed/altitude

As dxzh said very nicely, it's too bad that the newspaper needs to decide wether the crew made it right or wrong. In most cases, the truth is in between and we (as experienced professional) should be able to understand it clearly. It is absolutely not a matter of judging the crew, since they obviously are not the cause of the accident. Still, their actions could be analyzed for the sake of safety in finding how their actions could have been improved. According to Rainboe's attitude, I guess there wasn't so much of CRM during his 18 years of heavy 747 operations...

[Loose rivets]

There has to be some definition of 'pushing' or letting the nose down. It just can't have been a very pronounced maneuver.

Any attempt to sustain 14 degrees up as the speed came back towards the shake would be catastrophic, obviously. Somehow, that had to be corrected, and one would hope by just allowing the nose to come down a bit...accepting going below the glide, and trying to nail an attitude that was a last-ditch compromise.

I'll leave the flap setting out of the equation, as it may or may not have been just being part of that compromise.

[scrivenger]

Suninmyeyes I completely agree with your sentiments as expressed in para 2, however and very sadly there will always be professionals and professionals, so its not always that easy to leave it to the professionals....

On another note a quick question. Does the 777 fuel tank contain sensors for ice as well as water?

[Swedish Steve]

Does the 777 fuel tank contain sensors for ice as well as water?

Each tank has a water sensor. This works by sending a signal down through the fuel which is reflected off the tank bottom surface. The time the signal takes to make the journey is measured. If there is water or ice in the tank the signal will be reflected from the fuel/water (or ice) interface. The resultant shorter signal journey will trigger the water in fuel maint message. So yes the water sensing system will react to ice as well as water.


Originally Posted by Rainboe
instant flaps- they could take 20 seconds whilst sucking your elevator control dry of all power!

But retracting the flaps from 30 to 25 will only take a couple of seconds, and they had all hydraulics working so no loss of hyd pressure.

[BOAC]

I would dearly love this sniping between factions to stop! I said eons ago on this thread that I do not know what I would have done in that situation.

As I said before, given a significant loss of available energy on the approach (as any pilot, powered or glider should know) there is an altitude above which it is beneficial to reduce flap and/or lower the nose to maintain best glide performance. There is an altitude below which is is beneficial to use the remaining energy to 'stretch' the glide. They, deliberately or inadvertently, chose the second. I suspect that at the moment of stick shake and a/p disconnect at 170' there was an awkward feeling that the choice may not have been right. All said and done, no-one died and the aircraft crashed on the airfield.

However, we cannot judge with the information we have available. I sincerely hope that some sort of 'official' analysis is produced somewhere of the 'best' solution so that it can be added to that mysterious store of 'background' knowledge all pilots have. Until then, rantings about stuffing the nose down, hydraulics being sucked dry are pointless.

[Jumbo Driver]

Hear, hear!


JD
:)

[NigelOnDraft]

For all the bitching about the "attitude" / "GS" / "Speed".

Firstly, by leaving the AP in, you had 2(3) crew to discuss/action the best options in resolving the real problem, which lay in the engines... :{

For those of you who advocate lowering the nose to maintain the approach speed (~140K) the aircraft would have ended up well short* - unless you can also show us the profile as to when to now raise the nose / sacrifice airspeed.

The Flaps were retracted ~240' (IIRC) from 30 to 25. The 30 setting is almost all drag. I suspect this was inspired - the rate of loss of IAS would have been higher with Flap 30, so the stall / stick shake / end point would again have been earlier*.

I guess that with idling engines, a suitably trained and pre-notifed crew, it could be shown to have got to the threshold before landing. Lower nose, Flaps 25 (maybe 20?), even some ground effect - but it is barking mad to even suggest this crew should have tried it :ugh: Contrary to the emergency handling procedures we are all taught, and irrelevant as a "lesson" because next time it occurs 1NM further out on the approach all would change and it would not make the threshold* :{

The actions by this crew just got the aircraft over the A30 and onto wet / soft ground, and "landed" with a tolerable RoD that saved everybody.

*Now just go and look at the A30, traffic, and the trees along the SE side. If the aircraft had come down before there, or even "over" the road / trees at very low altitude, the results would likely have been catastrophic...

NoD

PS suggest we do not even discuss the Sim here - I really cannot believe it is accurately modelled for engines out / ground effect etc.

[scrivenger]

Swedish Steve thanks for the reply - the point I'm trying to clarify in my head is that will the sensor react differently to water than ice . It has been discussed quite openly that the water was a contributing factor after it had melted from ice, my point being that it appears that excessesive water in the tanks can be detected as a cause for concern but not neccesarily ice....

[snowfalcon2]

I tried to estimate the obstacle clearance of BA038's flight path by comparing the FDR trace and Google Earth. It appears to have crossed A30 about 5 sec before touchdown at about 100 ft height. At that point there is a low (15-20 ft?) building 50 metres from the runway centerline as well as streetlight poles.

The next significant obstacle is a group of houses 700 metres from the touchdown point, where the plane was 14 sec from touchdown at 230 ft, nose high just before the stick shaker activated.

With full respect for the crew's action in a situation they had obviously never been trained for:

The hypothetical question is, would a slightly lower faster approach, reducing the margin to the houses, have left the plane with enough additional energy to flare over the road and (presumably) come down softer than the actual 1400 fpm vertical speed?

A second question. What if the airplane would have "sounded the alarm" at the earliest possible time, which according to the trace was about 54 sec before touchdown for the right engine and 45 sec for the left, as the EEC entered "Control Loop 17"? An immediate flap retraction to 20 degrees at that early point in time might actually have given some real benefit of reduced drag, even considering the ~10 sec retraction time. But how much?

[Re-Heat]

Well you should not lurk because right now there's a dearth of wide bodied experience (and common sense) in these discussions on Rumours and News!
Hear, hear.

[NigelOnDraft]

The hypothetical question is, would a slightly lower faster approach, reducing the margin to the houses, have left the plae with enough additional energy to flare over the road and (presumably) come down softer than the actual 1400 fpm vertical speed? For "hypothetical" I would say "irrelevant" :ugh:

A second question. What if the airplane would have "sounded the alarm" at the earliest possible time, which according to the trace was about 54 sec before touchdown for the right engine and 45 sec for the left, as the EEC entered "Control Loop 17"? An immediate flap retraction to 20 degrees at that early point in time might actually have given some real benefit of reduced drag, even considering the ~10 sec retraction time. But how much?So you are suggesting that if the engines give a first indication of failure in an airliner, you want the crew to ignore all drills to do with trying to restore the engines, or even determine if the warning is/are false... and dive below the G/S, retracting flaps by (?) how much. And when would you do this? VMC? IMC? AWOPS? With Terrain under the approach path?

Take a clue from the AAIB - do they seem the slightest bit interested, at this stage, in the crew actions, or why the engines stopped :D

And are you seriously suggesting that as a result of this accident, we should look at training crews in unanticipated double engines failures on Final Approach, or might it be better to stop the engines failing in the first place :ooh:

NoD

[FullWings]

The hypothetical question is, would a slightly lower faster approach, reducing the margin to the houses, have left the plane with enough additional energy to flare over the road and (presumably) come down softer than the actual 1400 fpm vertical speed?
Very difficult to say, due to the unpredictability of ground effect, wind gradient, drag characteristics of a 'dirty' airframe, engines that were producing significant thrust, etc. It's something that would require large gonads to experiment with in this situation... If it was *obvious* that a crash into houses/trees/petrol stations was going to take place, then what have you got to lose? Otherwise, a very difficult call. I wouldn't rely on a simulator to give a realistic answer in this scenario either.

It is well known that you can often escape an undershoot situation by using the technique described in the question above. What is slightly less well known is that the aircraft are generally "cleaned up" on recognition of a developing undershoot and the potential energy (height) converted into kinetic (speed), then bled off in the ground effect where the wing is more efficient. If you have gear and drag flap deployed on an airframe where configuration changes are slow and/or require a significant energy input, the act of speeding up to get into ground effect will probably bleed more energy than you'll save later and lead to an even shorter landing. It isn't called "drag flap" for nothing; in an overshoot situation, "pushing against the flaps" is a another well-known remedy.

A second question. What if the airplane would have "sounded the alarm" at the earliest possible time, which according to the trace was about 54 sec before touchdown for the right engine and 45 sec for the left, as the EEC entered "Control Loop 17"? An immediate flap retraction to 20 degrees at that early point in time might actually have given some real benefit of reduced drag, even considering the ~10 sec retraction time. But how much?
The were no warnings (aural or visual) that anything untoward was happening. This is just one of the factors that made it a very difficult scenario to deal with. Does going into "Control Loop 17" mean the engine has become unresponsive? I don't have that level of knowledge but I believe it has something to do with surge/stall recovery, not a total failure. From a flight crew perspective, as it happened to one engine first, a warning would be noted but I suspect no action taken, as the 777 is perfectly happy coming in single engine F30, as the WAT limits are high in that config. By the time a warning came through for the other one, you'd be at the same place and time as the crew were on the accident flight.

It is easy to take the precise figures for BA38 and work out all sorts of things the guys might or might not have done. Change those starting conditions by just a small amount and the "best" course of action may change radically... It was a very dynamic situation and there was not enough information available at that instant to make calculated decisions - just instinctive ones. After all, here we are, eight months later, and no-one has definitively worked out what the optimum actions might have been...

[snowfalcon2]

And are you seriously suggesting that as a result of this accident, we should look at training crews in unanticipated double engines failures on Final Approach, or might it be better to stop the engines failing in the first place?

No. You might want to look at my post #1736 (http://www.pprune.org/rumours-news/340666-ba038-b777-thread-87.html#post4373610)to get confirmation on that point. This is a secondary issue, but not totally uninteresting, as many before me have shown :ouch: .

So you are suggesting that if the engines give a first indication of failure in an airliner, you want the crew to ignore all drills to do with trying to restore the engines, or even determine if the warning is/are false... and dive below the G/S, retracting flaps by (?) how much. And when would you do this? VMC? IMC? AWOPS? With Terrain under the approach path?

As BOAC has stated (and others before), there is an altitude (or point in the approach) above which reducing drag pays off anyway and I'm referring to that phase - I'm not sure this was the case for BA038. The suggestion would admittedly be bad in those cases where the time for the action (say 5 sec) delays the engine restoration drill AND the engines would actually have responded in the last 5 sec before hitting the ground. In all other cases it would do no additional harm. Either the airplane crashes anyway or the engines save it before, or - in the fortunate case - the airplane would increase its chance to make the airfield.

Take a clue from the AAIB - do they seem the slightest bit interested, at this stage, in the crew actions, or why the engines stopped

Finding the root cause is paramount. However, if it's not found with certainty, there might be reason to consider the handling of low level dual engines-outs. Time will tell. :ok:

[stickyb]

Each tank has a water sensor. This works by sending a signal down through the fuel which is reflected off the tank bottom surface. The time the signal takes to make the journey is measured. If there is water or ice in the tank the signal will be reflected from the fuel/water (or ice) interface. The resultant shorter signal journey will trigger the water in fuel maint message. So yes the water sensing system will react to ice as well as water.


Am I right in assuming that this detection method will only work when there is a distinct boundary condition - ie a layer of water or ice with a layer of fuel on top - as opposed to the situation where the tank just contains a mixed fluid?

[CONF iture]

But retracting the flaps from 30 to 25 will only take a couple of seconds, and they had all hydraulics working so no loss of hyd pressure
You're correct Steve.
Just to make things more precise, graph in P6 says 8 seconds.


Technically and aerodynamically speaking, I don't see where sispanys ria is wrong ?
For every flying machine, the same rule apply and an optimal attitude will stretch your glide.

Would I have done better ?
Certainly not !
Probably a case for heart attack and best case scenario a compulsory underwear change before jumping in the slide ...

I think that crew has been very unlucky to be on that BA038 but in the same time has been very lucky to end it up the way it did.
But the worst for them was probably to have to go for that PR BA BS the very next day.
For the medals, I'm not sure they really care but would rather have all the data in their pocket which I doubt they have been given ...

[Swedish Steve]

Am I right in assuming that this detection method will only work when there is a distinct boundary condition - ie a layer of water or ice with a layer of fuel on top - as opposed to the situation where the tank just contains a mixed fluid?

Yes it detects the boundary. The transmitter is very low in the tank so it is usually immersed in fuel, and the beam goes down to the bottom surface and back.

[pax2908]

Reading again ... could someone please clarify the following (on Page 10 of the report): "approx 6500 to 7100 kg of fuel had leaked [] before the spar valves were manually closed". I thought these valves would be closed when the fire handles are pulled. But the quantity above seems quite large (to me!) ... so what does "manually" mean here?

[BOAC]

Posts #5-#12 and on will explain.

[Jumbo Driver]

It really would help if people read the AAIB reports before asking questions. :ugh:

The answer to your question pax2908 is here (http://www.aaib.gov.uk/cms_resources/S1-2008%20G-YMMM.pdf) on pages 5 and 6 of the AAIB Bulletin S1/2008, published back in February, if you would care to read it ...


JD
:)

[dxzh]

FullWings and others well explain the practical uncertainties associated with the hypothesised alternative ways of handling the aircraft after the double rollback - particularly given the ever-developing critical position the crew found themselves in at literally the last minute and a slow, low, heavy aircraft in an initially stabilised but very draggy configuration.

The acid test in my simple world is that, if I were put back in the situation the crew found themselves in at that minute of that flight, then I would turn down each and every proffered "improvement" or “lesson” from any well-meaning speculator, who could (inevitably) only aver with less than 100% confidence that their alternative would work, in return for the certainty of the safe landing which the crew delivered on the day.

I think we should all be pretty humble and thankful that the crew did what they did with the poisoned chalice that they were given and that they saved the day. In my view the crew balanced the aircraft on the right side of the stall, they managed the little energy they had and got the right result, a safe landing - remarkable! This was a catastrophe which could have happened, but did not thanks to the crew.

[VNAV PATH]

sorry to be out of tune, but now starting to read all this thread !

somewhere written that the crew performed a managed approach .

what is it ?

thanks !

[DC-ATE]

dxzh -
>>> "I think we should all be pretty humble and thankful that the crew did what they did with the poisoned chalice that they were given and that they saved the day. In my view the crew balanced the aircraft on the right side of the stall, they managed the little energy they had and got the right result, a safe landing - remarkable! This was a catastrophe which could have happened, but did not thanks to the crew."


Ah, but how do we know that they might have made the runway had they left the flaps alone? Or might have gotten to the overrun. Granted things turned out alright, but they might've turned out better. We'll never know. And chances are the sim won't really prove anything. I just don't think their actions qualify them for any Flight Safety Award. Unless, that is, it can be proven that reducing the flaps at that critical point in flight was the right thing to do.

[dxzh]

DC-ATE, entirely fair comment on your part and I agree "We'll never now" - but I respect the crew nonetheless for what I do know which is that they got the plane down safely having been put into a potentially catastrophic situation by the double rollback - I would not begrudge them any praise for that achievement.

[Carnage Matey!]

And chances are the sim won't really prove anything. I just don't think their actions qualify them for any Flight Safety Award. Unless, that is, it can be proven that reducing the flaps at that critical point in flight was the right thing to do.

I believe Boeings computer modelling has already proved that reducing the flaps was the right thing to do. Unless landing even shorter and ploughing through a busy road is considered a better outcome.

[777fly]

It has been suggested in this thread that crews are not trained to cope with a total loss of power at low altitude. I would propose that this is not so. Just consider the regular practice, in the simulator, of recovery from windshear or GPWS warning. In both cases, the aircraft is flown in such a way as to trade kinetic energy for potential energy, in a situation where engine power cannot meet the desired flight profile. In other words, trade speed for height. In these situations, kinetic energy is traded for height right back to the stick shaker, at which point attitude is adjusted to fly at intermittent stick shaker speed.
I would suggest that the crew of BA038 did, instinctively, follow exactly what they had been trained to do. Speed was bled back to the shaker speed and then an attitude adjustment was made to keep the aircraft flyable. Energy management.
There seems to be a perception that the stick shaker represents an entry into the stall regime, with loss of lift and control. This is totally wrong. The aircraft remains controllable and flyable at shaker speeds, as there is still a fair margin above the stall speed.

[DC-ATE]

I know about stick shakers having heard them numerous times in the sim; fortunately NEVER under actual conditions!

There is an obvious dissagreement in the handling of this flight with regard to flaps. I don't care what type airplane it is, however, if you raise the flaps, you've taken away lift and increased the stall speed: period. Any other action taken at that point other than lowering the nose will only aggravate the situation. As I stated earlier, I've had the flaps dumped on me and I know the feeling!

Being as I'm retired, I'll leave this now (unless called upon) to all you active types to sort out.

Again, we're ALL glad the outcome was as successful as it was. It probably speaks well for the aircraft also.

[awblain]

What options did the crew of BA038 have with respect to trading speed/kinetic energy for height/potential energy?

They had a finite reservoir of total energy, unless they could get power back. Worse, in fact, this energy reservoir was being depleted rapidly by drag: bleeding away into the turbulent air behind the flaps.

Going faster would increase drag further, taking away a larger fraction of their total energy per second. Going slower would reduce the loss rate, but too slow and what remains is forfeit in a stall.

The results of the manufacturer's detailed modeling of the precise circumstances: go for a bit less lift and quite a lot less drag, and squeeze the remaining energy out for as long as possible. The crew's intuition seems to have lead them to the same (right?) answer. A remaining question - does the computer modeling take into account the details of ground effect, surface topology and gusty wind in the final seconds?

[777fly]

Sorry DC-ATE, but I disagree. Retracting flap from 30 to 25 on a 777 has virtually no effect on lift, changes the stall speed by a negligible amount, but considerably reduces drag. In the energy management situation I recently described, it is a winner.

[DC-ATE]

OK 777fly, I'll leave it to you to keep these things in the air. Best of luck to you and your fellow pilots. Just glad I'm out of it.

[snanceki]

@777Fly.

I do not question your response to DC-ATE. or agree with his post. but simply ask...

What is the purpose of the 30 position IF it adds "negligible" lift yet adds considerable drag.

Surely the "negligible" must be closer to "significant" i.e. worth having or otherwise what is the point of such a setting?

I do not wish to rekindle the discussion re whether the crew should or should not have reduced the flap setting (I'm not interested and do not believe that at this point it has any relevance) but just question the premise against which the discussion is based, namely that 25 to 30 is "purely drag".

I am not a pilot. nor an aerodynamic specialist, but as an engineer I find it surprising that a function/position has been provided that increases drag but not lift...unless of course its purpose is as a brake, which may be the case.

So another way. What is the thinking/purpose in selecting 30 vs 25 under normal circumstances other than procedure calsl for it.

Please enlighten us.

[NigelOnDraft]

snancekl
but as an engineer I find it surprising that a function/position has been provided that increases drag but not lift...unless of course its purpose is as a brake, which may be the case.Effectively the case. On the 757, Vref F25 was only a couple of knots above that of F30 - however, it gave you much mroe drag to keep the power "up" on Final Approach, enabling better speed control / engine response.

The airlines have now seen this and are getting 777 pilots to do F25 landings, and us Airbus guys to do F3 (Flap 3 rather than Flap Full). This keeps the Final Approach power low hence saves (a little) fuel. Depending on type the Approach and speed and Landing Distance increase by a bit, but the main effect for the crew on a steep glideslope / tailwind is dififculty having anything other than idle, against an SOP requirement of "Approach Power".

It makes the selection of F25 fairly instinctive, when day in / day out you are used to seeing a lower power setting for a F25 approach than a F30... someone takes the power away, lets go for the approach that needs less power :D

As has been pointed out elsewhere, most airliners on a go-around call for an immediate reduction of flap setting by one or even 2 stages - yet no increase in datum speed. Again, reason is pronounced reduction in drag (increased climb performance) with little reduction in lift.

NoD

[cwatters]

Increasing drag allows a steeper approach without building excess speed.

[HarryMann]

Increasing drag allows a steeper approach without building excess speed.

Another way of putting it is that its got a lot to do with the drag curve; trying to get the profile drag up Vs the induced drag so that one does not sit on the 'back of the drag curve', a potentially speed-unstable place to be.
As has been said, also allows keeping a higher power setting so there is much better speed control of both engines and aircraft.

[dxzh]

I would like to try and take a step back and explore why current sumping procedures, even when correctly applied, might be inadequate and allow significant water (whether free or entrained/dissolved) to accumulate in the 200-ER model centre tank in certain narrowly defined cold, but within certificate, conditions. By significant I mean capable of causing a restriction in a fuel line, not that it would prevent the fuel burning in the engine.

It seems important since the accumulation of significant water in the centre tank may be a contributory factor in creating the unusual restrictions in each fuel line of BA038 which triggered a double rollback.

1. Centre tank accumulation of free water

There seems to be a recognition unconnected with BA038 that significant water can build up in the centre tank and restrict fuel lines:

- the Boeing-issued 777-FTD-28-07002 (as revised 20 Feb 2008) at JetPhotos.Net Forums - The Friendly Way to Fly - View Single Post - BA 777 landing accident at LHR (http://forums.jetphotos.net/showpost.php?p=459941&postcount=887) (and for a more summary version not mentioning 200-ER see http://www.pprune.org/3958000-post608.html) mentions that the 200-ER centre tank is reported to have accumulated water which has frozen and restricted the flow of fuel along at least the jet pump driven fuel scavenge lines.

- In the absence of any information on the water content of the fuel in the BA038 centre tank due to the damage on landing, this FTD seems to offer at least some strong circumstantial evidence of the accumulation in similar centre tanks of water and ice on long, cold flights and that this ice is capable of causing restrictions in fuel lines - this seems worth mentioning in the context of the BA038 analysis. In particular, I note from the FTD that:
• while the freezing water is causing restrictions in part due to cold temperatures in the centre tank, the freezing appears also at times to be due to the centre tank water being subjected to the even colder main tank fuel temperature.
• the centre tank is prone to the build-up of water sufficient, if not properly dispersed within the fuel, to cause enough icing in the fuel scavenge lines to restrict them in part or completely.
• free water built up is only dispersed by the operation of the water scavenge and when this is not operating the free water sinks to the bottom and is drawn into the fuel scavenge lines.
• also without mixing by the water scavenge pumps, entrained and dissolved water in the centre tank fuel is likely to separate out and end up in the OJ or fuel scavenge pick-ups.
• the pipe which takes the centre tank fuel to the outlet in the main tank on the outboard side of the wing is extended a little further outboard in the 300ER and that this extra distance in itself, due it seems to the cooling effect of the cold-soaked main tank fuel, may contribute to the accretion of ice in the fuel scavenge line sufficient to block it.
• corrective action in the centre tank on the 300-ER is being taken to move the water scavenge inlet closer to the fuel scavenge inlet to minimise ingestion of free water in the fuel scavenge line.
• 200-ER centre tanks (ie like in G-YYYM) are not covered by the FTD but ... the FTD notes that “One operator advised of this problem [of restrictions due to ice in fuel scavenge line blocking scavenge to main tanks] occurring to a lesser extent on the 777-200ER model as well.”
• the underlying cause of free water in the centre tank is not addressed, nor is the fact that the water scavenge does not operate to disperse water after the OJ pumps are turned off.
• there is a contributory factor here common to BA038 in that the FTD states that: “A review of operator QAR data to date shows that this problem primarily occurs on long distance flights from Europe, suggesting a potential operations component to the problem, but long distance flights from JFK have not been affected. Further review shows the problem to primarily occur between the months of October - April, suggesting an ambient ground temperature component to the problem.”. Is this a coincidence?

- There is no indication of the highest levels of free water which operators have found in affected 777 centre tanks (eg: 1, 10, 100 litres?) – does anyone know?

- Water will accumulate in the centre tank:
• where (a) there is free water or dissolved/entrained water in uplifted fuel; or (b) water condenses in centre tank during flight or ground turnaround, AND in each case, if it is not removed from the centre tank because it has separated out of the fuel and frozen or hidden itself in pockets inaccessible to the OJ pump or fuel scavenge or sump drain valves, then in the next sector one starts off with a base amount of water in the centre tank derived from (a) and (b).
• The next uplift of fuel may melt and/or disperse it (by entraining or dissolving it) but not necessarily or permanently.
• The process will repeat itself until the environmental conditions cease to apply or some other event intervenes as it normally would to cause the water to be consumed by the engines or drained.

- the volume of water contained in an uplift of properly specified fuel for a long sector is no more than a few litres so, if significant volumes of water are to be explained in the centre tank, it would seem condensation would need to be responsible. However, condensation from air drawn into the centre tank to replace fuel drawn out would, particularly at high altitude, have minimal water content (much less than a litre!). To explain higher levels of water from condensation there would seem to need to be a stream of outside air coming into the centre tank, preferably at low altitude. Question whether sufficient circulation might be provided by either:
• the continued operation of the two jet pump fuel scavenge lines after the fuel is scavenged in the last hours of flight at the end of each sector; and/or
• the descent at the end of each sector with an empty centre tank into humid air at ground level?

2. 200-ER centre tank - layout

- There are various baffles across centre tank and other dead spots in which free water may accumulate. The floor of the centre tank becomes more curved in flight and this may also hinder ensuring free water's dispersal in the fuel at certain times of flight. The layout of baffles in the central section of the centre tank can be seen in figures 6, 11 and 12 in the AAIB report produced in respect of the omission of G-YMME’s purge door at http://www.aaib.dft.gov.uk/cms_resources/G-YMME%20Section%201.pdf but there are also significant ribs in the colder inner wing section of the centre tank.

- There are only two sump drain valves in centre tank – would anyone be able to point out (on picture of centre tank mentioned above) exactly where the two sump drain valves are located on lhs and rhs, relative to low points, baffles, OJ pump inlets and fuel scavenge inlets?

3. Weaknesses in detection of water

It seems difficult for operators to monitor easily whether free water or dissolved/entrained water is accumulating in the centre tank and thus they may allow a contributory factor to a double rollback to develop. Issues include:

- Sumping would only have a chance to remove free water if: the free water has had a chance to settle or (if the water has frozen) the ice had had a chance to melt and then settle and in each case such free water is not in an inaccessible blackspot as a result of the baffles or compromised location of the sump drain valves. Anecdotal evidence suggests that one or more of turnaround times, OATs and centre tank design (among other things) may effectively hinder these conditions occurring in long cold-soaked back-to-back winter sectors.

- Sumping will not work properly in cold conditions and is therefore potentially an unreliable procedure if required to ensure safe operation.

- Are Karl Fischer (or similar) tests to be routinely conducted several hours after uplift of warm fuel into cold-soaked centre tank at cold stopover as part of the routine Boeing/operator recommended sumping procedures on daily/transit basis I wonder? If not, then melted and dispersed ice in warm fuel uplift is arguably unlikely to be detected anyway and even then may require pumps to be run for some period before testing (though perhaps running pumps would not help sumping of free water)?

- If the water scavenge pumps operate successfully after a warm uplift to dissolve or entrain melted ice into the fuel in manner, then water sensors, which can only indicate if free water has melted and settled to the bottom of the tank, also seem imperfect as an early warning of significant levels of entrained/dissolved water. It is not even clear that excess free water MMs which are triggered are seen as significant in any event, or have immediate pre-flight or in-flight remedial actions/procedures associated with them? In particular:
• Excess water maintenance messages are not drawn to the attention of the pilot (unlike say an EICAS advisory or caution say about low pump pressure). The excess water maintenance message seems to self-clear even if correctly triggered.
• It is only designed to be triggered in centre tank if more than 627 litres (138 gallons) or so of free water is settled at bottom of particular part (any idea which?) of centre tank. This is insignificant amount in context of burning 80 tons of fuel but even a part of such amount might represent more than enough water, suitably frozen, to create a significant restriction in each of the fuel manifolds.
• Perhaps, if free water in the centre tank is seen to be a contributory factor of the double rollback of BA038, more prominence needs to be considered for this message?

- perhaps in winter after each couple of long very cold sectors out of LHR test all of the centre tank contents by draining the centre tank in a warm hangar and then examining and measuring whatever else was inaccessible in the centre tank by opening it up. Also perhaps to repeat process but on final sector to disable fuel scavenge completely (though this might reduce centre tank condensation (if any) too) in order to enable examination of contents of 800kg of remaining fuel for any build-up of free, dissolved or entrained water. The key seems to be to test the correct categories of flight legs and not simply to rely upon a sump test.


4. Centre tank scavenge

It may be worth considering, for more risky types of long, cold flights:

- scavenging the centre tank fuel into one main tank only in order to break the centre tank fuel being a common cause of a failure condition and to preserve the independence of the main tank fuel supplies to each engine? Downside would be an imbalance between the main tanks.

- not running the fuel scavenge pump when the centre tank is empty, by removing the motive power to the fuel scavenge after 30 or 40 minutes of operation (or no later than centre tank indicating empty)? Otherwise is there a risk that continued operation of the fuel scavenge while the centre tank is empty:
• could draw into the centre tank towards the latter stages of the flight a significant stream of (potentially humid) cold outside air from the vents (causing unnecessary condensation build-up)?
• could result in a significant volume of air being entrained into the main tank fuel (causing issues by its likely release at high altitude elsewhere in the fuel supply system)?

- requiring a water scavenge at all times while the centre tank has fuel in it, rather than just when the OJ pumps are working, in order to minimise the settlement and accumulation of free water in 800kg of fuel remaining after the OJ pumps are turned off?


5. Centre tank OJ/jettison check valves

Is there any possibility of undiluted centre tank water being injected directly into the fuel manifolds without passing through the main tanks first?

- The AAIB’s comment in a different context about the possibility of the OJ/jettison valves opening to admit air from the centre tank into each fuel manifold if pressure difference was sufficient presents an intriguing prospect if it might also allow the possibility of dregs or slugs of free water (maybe a bucket or two) being swept into the cold-soaked main tank fuel in each fuel manifold towards the end of the flight.

- Pressure differences as a plane rapidly descends are to be expected – the fuel manifold might just be at least on a localised basis be at lower pressure temporarily, perhaps as a result of having pockets of undissolved air in it (if the scavenge pump’s operation while dry could provide a mechanism temporarily to introduce air into otherwise unsaturated fuel) which might allow the centre tank pressure to overcome each OJ/jettison check valve.

- However even then would water be able to pass through each switched-off OJ pump with the same ease as air say?

- Clearly more than one contributory factor is required for undiluted centre tank water to end up in each fuel manifold at the end of the flight, but it might offer an alternative explanation as to how significant water might unusually move into each fuel manifold, near simultaneously, towards end of flight, sufficient to cause a restriction to each engine and without increasing the concentration of water in the main tanks.

- Should there be a cut-off valve (in addition to a pressure dependent check valve) which could be closed after OJ pumps turned off to ensure that this could not happen? Is there a safety reason why the operation of the OJ/jettison check valve must be allowed after OJ pumps turned off?

[philipat]

NigelOnDraft:


It makes the selection of F25 fairly instinctive, when day in / day out you are used to seeing a lower power setting for a F25 approach than a F30... someone takes the power away, lets go for the approach that needs less power :D




Now that you put it so simply it would indeed explain the actions of the crew. Your inputs regarding the prevalence of F25 landings, it also makes it more difficult to understand the critics. This certainly was a rapid descent with (Very) low power.

[Re-Heat]

Notwithstanding the fact that fuellers are unwilling to resell fuel that has been offloaded, at carriers' home bases, I could envisage centre tanks being emptied entirely prior to refuel as a result of this, though greater fuel line heating throughout flight may be the answer.

However, as the AAIB point out, the flight profiles were extremely rarely encountered - I would like to know how rarely they have been encountered on back to back sectors as in this case in their next report.


Regarding flap - from day 1 of flying training in single-engine piston aircraft, people are taught to get rid of drag flap upon engine failure to stretch the glide.

Anyone commenting here who questions the elimination of drag flap should, I feel, return to the basic books and relearn what they clearly have forgotten. It was neither a typical glider whose aerofoils are distinctly differently designed, nor a procedure for which they had trained - the instinctive response is to be applauded.

Drag flap permits a combination of more rapid speed decay without power, and a more suitable deck angle at final approach. Perhaps if someone has a suitable 777 graph, this pointless diversion to the thread can be put to rest?

NoD puts it best:
As has been pointed out elsewhere, most airliners on a go-around call for an immediate reduction of flap setting by one or even 2 stages - yet no increase in datum speed. Again, reason is pronounced reduction in drag (increased climb performance) with little reduction in lift.

[snanceki]

Thanks for the replies against F25 vs F30.

From what you guys have said looks like F30 vs F25 is more of a brake and engine control feature rather than low speed lift assist otherwise procedures wouldn't have been changed to use F25 ilo F30 if I understand the replies correctly.

Maybe its unwise to raise the issue but I warm to the explanation of "intuitive action".

Seems logical from my limited understanding perspective.

[777fly]

snanceki:

I think your question has been answered above. No further comment required from me.........

[windytoo]

CONF iture, your post said it all. Luck of both sorts contributed hugely to this accident and the amazing lack of casualties associated with it.

[cockney steve]

As SLF, I may be missing something, but having a fair bit of experience with Diesel-powered vehicles, I am struck by the cold operations similarities.

It seems odd that the pumping-system, with huge overcapacity/redundancy, could be used more effectively, in conjunction with the oil-cooler.

Again, It seems strange, from my simplistic viewpoint, that oil is first air-cooled,THEN dumps surplus heat into the fuel.

Also mentioned, this overheats in cases of low fuel-flows, to the point where fuel is burnt purely to circulate and reduce temps.
It's self-evident that Airliners are designed to operate mainly in high,cold conditions....they only pass through "warmer" environments on their way to and from their main environment.

SO, why is the "waste" heat, from the oil ,not fully utilised to warm a full-flow RECIRCULATING fuel system? no doubt there are also other sources of "waste" heat,within the engine -system...but full-flow would , with appropriate by-passes / pressure spill-off etc. keep the lube oil cooled and warm the fuel.

Yes, I appreciate that warm fuel is considerably less dense and therefore contains less energy per unit-volume, but I don't see big elastic bands at the airport, launch -assisting on hot summer's day :}

just about all road-vehicles (petrol and diesel) are fuel-injected,nowadays (emissions control! ) Invariably the pumps have surplus capacity over peak demand and all surplus spills off to a return to the tank....so I'm not inventing anything, just suggesting that maybe aircraft designers should think laterally.

(maybe they have and i'm talking bollocks! :\ )

[sispanys ria]

At a given configuration, the only thing that matter to achieve the longest gliding distance is the AOA. The best gliding distance is obtained at L/Dmax. Beside following the GS is useless as it leads far beyond the threshold, this leads to increase the AOA, building up drag thus highly reducing L/D and gliding distance. Energy is a factor of force by distance. The more you spoil in drag trying to follow the glide, the less distance you can fly. Once no more kinetic energy is available (stick shaker), the only one available is the potential energy, which is also based on distance... but only the vertical one. The potential energy will anyway be used till the plane reaches the ground, what matters is to improve the L/D in order to spread the use of the kinetic energy. The drag reduction between 25 to 30 is probably meaningless compared to the generated drag at a 16 degrees nose up attitude.

http://www.aerostarwind.com/images/384_Airfoil_Lift_Drag_Graph.jpg

[scrivenger]

dxzh thanks for the info - 2 items that stand out from your post from my point of view are :-

1 - • Excess water maintenance messages are not drawn to the attention of the pilot (unlike say an EICAS advisory or caution say about low pump pressure). The excess water maintenance message seems to self-clear even if correctly triggered.

2.-• It is only designed to be triggered in centre tank if more than 627 litres (138 gallons) or so of free water is settled at bottom of particular part (any idea which?) of centre tank. This is insignificant amount in context of burning 80 tons of fuel but even a part of such amount might represent more than enough water, suitably frozen, to create a significant restriction in each of the fuel manifolds.

Can somebody confirm to me that the two ponts above are absoloutley correct. That is to say that the excess water message will self clear and that approx 138 gallons is the amount of water that could be in the tank prior to any sensor being activated.

[Feathers McGraw]

NigelonDraft wrote:

"suninmyeyes - excellent post, especially the second para about us not saying half of what really goes on, since we just then get attacked by all the MS FSim experts"


While I can understand your frustration with how this is interpreted, the little snippets that emerge from those in the know are fascinating in their own right and I prize them for that fascination.

There may well be people that don't understand the realities of flying and moan and carp about procedures they can't comprehend, but to those of us that know enough to not do that but can never be flight crew because our bodies let us down at the first hurdle these chances to experience that "Oh I _see_!" moment are really valued.

Please keep letting the odd one slip here and there....

[cwatters]

We need to be a little careful when we say that the conditions for this flight were unique. The AAIB only say the flight is "unusual within the 13,000 flights analysed" and only IF you look at two factors together:

a) the fuel temperatures
and
b) the fuel flow rate during step climbs and on approach.

If it turns out that one or other of the above wern't a factor in the accident then all of a sudden the flight isn't that unusual. They found 280 flights with colder fuel temperatures for example.

The AAIB do use the word unique, but in the context of this being a unique accident.

[ChristiaanJ]

We need to be a little careful when we say that the conditions for this flight were unique.It's what keeps bothering me too.
So far, nothing yet points to something 'uniquely unique' in what? 6.5M flights?
Yet we do not have 777s scattered just short of the threshold all along similar 'cold' routes.
So where are the other Gruyère holes that lined up?

CJ

[L337]

It was a little unique in the airframe operating back to back "cold" flights. So the fuel never had a chance to warm up. Relatively speaking.

Was the water in the fuel, ever water long enough to be drained?

[ChristiaanJ]

It was a little unique in the airframe operating back to back "cold" flights.For the first time ever in 6.5M flights? I don't believe that.
Was the water in the fuel ever water long enough to be drained?That on the other hand sound like a more plausible question.
The excess water maintenance message... is only designed to be triggered in centre tank if more than 627 litres (138 gallons) or so of free water is settled at bottom of particular part (any idea which?) of centre tank.I find myself staring at a figure for water (138 gallons in the centre tank alone!) more than two orders of magnitude larger than the the 5 litres (40 ppm) quoted in the AAIB report, yet "acceptable" before an EICAS advisory message is triggered?

For the moment, most of our assumptions and guesswork are all wrong somewhere, or BA038 would have happened far earlier, and maybe not with the same outcome....

But since it happened on BA038, it's lurking somewhere to pounce again.... so I'm among those that hope a plausible "probable cause" will be found, and if I can contribute my minute bit to that... so much the better.

CJ

[L337]

For the first time ever in 6.5M flights? I don't believe that.

That is why I wrote "a little".

Regarding uniqueness, it is not the 6.5million flights, but how many of those 6.5 million were a 777. And of that number how many were that variant, and that configuration, with those low temperatures mixed into the cooking pot.

6.5 million is a red herring.

[Swedish Steve]

Notwithstanding the fact that fuellers are unwilling to resell fuel that has been offloaded, at carriers' home bases, I could envisage centre tanks being emptied entirely prior to refuel as a result of this, though greater fuel line heating throughout flight may be the answer.

They will not resell fuel because they don't know what it is. It may come out of an airliner tank but it will be a mix of Jet A and Jet A1 and even Chinese fuel. So they give it back to the airline it came from.

Centre tanks are always empty before refuelling starts. Do you envisage someone removing the dregs?

I find myself staring at a figure for water (138 gallons in the centre tank alone!) more than two orders of magnitude larger than the the 5 litres (40 ppm) quoted in the AAIB report, yet "acceptable" before an EICAS advisory message is triggered?

I believe the B777 was the first aircraft to have a built in water detection system. The reason for the 138gallons is that the bottom of the centre tank is flat. This is why the boost pumps are switched off with 800kgs remaining, and the rest sucked out by the jet pumps,
In hindsight perhaps Boeing should have made the EICAS message a Status message which the pilots could see.

[Rainboe]

333333333333333333

[Green-dot]

FAR 121, App. M, Item #43. Additional engine parameters:
There are several parameters such as vibration level, N2, EGT, Fuel flow, N3 and:

Fuel cut-off lever position. Is this the only parameter that is recorded to determine spar valve position? FAR 121, App. M does not mention any (required) parameters for recording spar valve position other than fuel cut-off lever position.

If the premise is that spar valve control has been tested and could not be demonstrated to fail under any condition, would the tests (investigating BA38) have been a duplication of tests performed during certifiation of the control system? If so, would there have been a reason to add any FDR parameters other than the required fuel cut-off lever position to determine spar valve position if the system was tested as fool-proof during certification?

The AAIB state: "Any uncommanded movement would have been recorded on the FDR and warnings would have been enunciated on the flight deck."

FAR 121, App. M only mentions the fuel cut-off lever position as a required recorded parameter, does this mean that any additional parameter must have been added by the manufacturer or as a JAR-OPS requirement? After checking JAR-OPS 1.715 table A1, table B and table C, applicable to the 777, I could not find any such requirement.

Referring to warning enunciation on the flight deck regarding spar valve position. The warning I am aware of is presented only when there is a disagree between the spar valve control relay position and spar valve actuator position as a result of a jammed actuator. According to the AMM/SDS, OPAS monitors control relay position and valve (actuator) position. As long as the spar valve actuator follows control relay position, there is no warning (no status message on EICAS). Even if for whatever (very remote) condition the control relay would move from open to closed position uncommanded with fuel cut-off lever in the run position. As long as the valve actuator follows control relay command there will be no warning presented on the flight deck because OPAS does not sense a disagree between these two components, hence, sends no fault message to AIMS. OPAS does not monitor a disagree between fuel cut-off lever position and spar valve actuator position.

Spar valve position can be displayed to the crew, but only if the crew selects the fuel synoptic or maintenance pages. Neither are likely to be selected during an approach phase unless there is a specific reason to do so.

It would have been interesting if the FDR parameters (and which parameters) for the spar valve positions were included in figure 2 of the interim report. Perhaps they will be included in the final report.


Green-dot

[Fragman88]

Just tripped over this in a US flight safety article:

`Or, as legend R.A. "Bob" Hoover has been quoted, "If you’re faced with a forced landing, fly the thing as far into the crash as possible.".

Probably not that relevant to these chaps as so little time to assess and act, but I will certainly listen to any thing said by Bob Hoover, and a nice refreshing reminder from an Ancient Aviator (with apologies for the `Ancient').

:ok:

[infrequentflyer789]

FAR 121, App. M, Item #43. Additional engine parameters:
There are several parameters such as vibration level, N2, EGT, Fuel flow, N3 and:

Fuel cut-off lever position. Is this the only parameter that is recorded to determine spar valve position? FAR 121, App. M does not mention any (required) parameters for recording spar valve position other than fuel cut-off lever position.


Modern DFDRs can record hundreds (if not 1000+) of parameters - way more than the minimum required set, plus they have the QAR (which may record even more) for almost all of the flight (including through the onset of the problem).

I think it is highly likely that the AAIB have spar valve position data, their statement is that the data shows valve open, not indicated open or commanded open. They also state that movement (even uncommanded) "would have been recorded", which implies to me that there are FDR parameter(s) recording actual position as well as commanded.


If the premise is that spar valve control has been tested and could not be demonstrated to fail under any condition, would the tests (investigating BA38) have been a duplication of tests performed during certifiation of the control system? If so, would there have been a reason to add any FDR parameters other than the required fuel cut-off lever position to determine spar valve position if the system was tested as fool-proof during certification?
They don't actually state that they couldn't make it fail, they state that they couldn't reproduce "uncommanded and unrecorded" movement (my emphasis) - which is actually quite a different premise. They then infer that there was no failure because none was recorded, rather than because it was failure proof.


Referring to warning enunciation on the flight deck regarding spar valve position. The warning I am aware of is presented only when there is a disagree between [...]
I don't know enough about 777 instrumentation to be sure, but I believe that on older boeing types there was(is) a spar valve light that indicates closed and transit. It would be interesting if that has been lost (or relegated to a maintenance page) going to glass cockpit. However, I also think that the AAIB must have some basis for their statement that warnings would have occurred.

It would have been interesting if the FDR parameters (and which parameters) for the spar valve positions were included in figure 2 of the interim report. Perhaps they will be included in the final report.
I agree - but on the other hand they may regard a flat line graph as superfluous if they believe they have already stated the same in words.

Don't get me wrong, I quite liked your spar valve theory, and the AAIB clearly also thought it was a line worth investigating - but I do think it is looking a little dead now.

[I have to admit I don't like the ice conclusion, I feel I need to re-read and digest the report a bit more, but it does seem to be what's left when they've eliminated other things, rather than driven by positive evidence. Feels very unsatisfying as a conclusion (even interim).]

[infrequentflyer789]

That is why I wrote "a little".

Regarding uniqueness, it is not the 6.5million flights, but how many of those 6.5 million were a 777. And of that number how many were that variant, and that configuration, with those low temperatures mixed into the cooking pot.

6.5 million is a red herring.

6.5 million is hours not flights (1.4M flights) - but it is all 777s (in fact all RR powered 777). That does cover several variants however, and fuel tank configuration is different between the variants, which may well be significant.

Of those flights, they've only looked at (only got?) data on 13,000 RR powered 777 flights, and the conditions are unusual within that set of data.

[sydneymike]

but it does seem to be what's left when they've eliminated other things, rather than driven by positive evidence. Feels very unsatisfying as a conclusion (even interim).]


My sentiments entirely. And, therefore, in the meantime it COULD happen again. Even if the chances are only 1 in 13,000, why take it if alternatives are available. Most of my circle of frequent flying business travellers now selects flight carefully on longhaul NE Asian/Europe flights to choose the 744. Ice or otherwise. Maybe irrational, and was ridiculed earlier, but the fact is there is a PERCEPTION amongst frequent flyers (Who DO know one end of 744 from the other end of a 772/3ER) that this airplane has unidentified problems and should be avoided until otherwise.

[snowfalcon2]

by rainboe:
Fall below a certain speed and the windmilling speed may not provide the hydraulic power you need to operate your flying controls and flaps- possibly about 160kts airspeed. In fact operate flaps and you may then lose flying controls with no pressure left for them!

With all respect,
Can someone confirm that the FARs would allow this condition? From what I've quickly gleaned (Gimli Glider) the RAT should always provide enough hydraulic pressure for the primary control surfaces.

[L337]

6.5 million is hours not flights (1.4M flights) - but it is all 777s (in fact all RR powered 777). That does cover several variants however, and fuel tank configuration is different between the variants, which may well be significant.

Hours not flights. I stand corrected. Thanks.

PS. No RAT on a 747-400.

[PJ2]

snowfalcon2;

It is true that the RAT will stall out if the a/c is permitted to fall below a certified airspeed which is about 140kts if I recall - I'll have to check the manual. The RAT on early 320s was subject to interference from the nosewheel slipstream - can't remember what was done to rectify the situation - perhaps the starboard offset, not sure.

[dxzh]

A few more thoughts related to centre tank pump inlets:

- Each OJ pump must be able to pump, while in climb and then cruise, 99% (as in (80t- 0.8t)/80t) of the fuel out of the centre tank before the inlets are free from the remaining fuel. The OJ pumps free of fuel, lose pressure and are subsequently switched off - the main tank boost pumps, which are permanently on, maintaining flow to engines in the meanwhile. In this case, the centre tank reduced to a little under 750kg indicated at its lowest at the time of the engines switch to main tank supply, before apparently increasing for some reason by 125kg or so to 800 kg indicated a few minutes later.

- Each OJ pump inlet is raised from the floor slightly and is in fwd part of the centre tank. What exact depth of liquid on top of floor (or liquid on top of ice on top of floor) immediately below the fuel pump inlet is required to submerge OJ pump inlet? How localised could that depth of water be given the geometry of the tank, position of ribs and the tank's shape during flight? Can anyone produce a diagram of exactly where everything is at the bottom of the tank near the OJ pump inlets?

- I assume that the fuel scavenge worked given drop from 800kg indicated to 0kg but ... given the knowledge that on cold flights like these that it is not uncommon for some of the fuel scavenge pipes to become blocked by ice, what would happen if the fuel scavenge lines local to the fwd positions on the left hand side and right hand side of the tank where the OJ pump inlets are were iced up, but the scavenge lines in the centre of the centre tank were working?

- I note from the rate of scavenge in Figure 1 the rate increased as the level of fuel indicated declined to 0kg. Could that suggest that as the level lowered: the rate of scavenge appeared to increase as less fuel/free water was accessible than expected as it was trapped where the scavenge lines were not working locally; and/or an expected increase given the vagaries and the geometry of tank?

Is it a red herring even to contemplate the boost pumps or centre tank pumps allowing the passage of fuel/water when they are selected OFF? I guess the premise of the suction feed test on the ground (as a pure test of the suction feed) would be flawed if it was a possibility that an engine-driven LP could draw fuel through any of the unpowered pumps from centre tank - and thus I would like to discount the idea completely. Yet as a Mad Hatter is drawn to a tea party, I am curious about the possibility given the suggestion in the interim report that air at least might possibly pass through the OJ/jettison check valve (and presumably therefore through the OJ pump when selected OFF too) ...

[lomapaseo]

Modern DFDRs can record hundreds (if not 1000+) of parameters - way more than the minimum required set, plus they have the QAR (which may record even more) for almost all of the flight (including through the onset of the problem).


Kind of like a computer with a hundred USB ports for data inputs. But do you have a hundred devices to hook up to these ports?

It ain't the DFDR recording limitation that just meets or slightly exceeds the regulated requirement, it's the availability of aircraft system sensors and wire routings that sets the actual limit.

With that said I really don't know what parameters were recorded for BA038

[coool guy]

I certainly believe the AAIB are very trustworthy and honest people simply trying to do thier best in what seems an unfathomable case.
However there are naturally those conspiracists who will always look for a cover up, bribery, corruption in any organisation and lets face it it can happen.
It should therefore be incumbent upon the board to be as transparent and straightforward as possible in all their reports and findings to the public.I have read all the 5 reports and all the posts on this thread. The reports are comprehensive and well written but that doesnt mean we cant criticise them!
My criticsim is this. Not once before did the AAIB mention the actions of the crew and I agree with Nod that the AAIB have never shown much interest in those actions, clearly focusing all their attention on fuel interuption and its causes.
So why do they now suddenly tell us that it was the first officer who disconected the Autopilot and selected flap 30? and why is this more relevant now that they have established that ice is the cause?
They must have known those facts from the very beginning but declined to tell us about it. I am sure it is not the case that they are trying to hide something but nevertheless it gives ammunition to those who think they are!
Why cant they just lay all the facts on the table from the start without worrying about whether it is relevant or not or who it might hurt or what the consequencies might be or the costs to the industry etc etc

[dxzh]

1. Main tank water scavenge

If centre tank fuel scavenge pipes can ice up, perhaps the main tank water scavenge ones could in certain conditions too? Maybe a scenario with cold-soaked fuel in each main tank at critical icing temperature at end of flight with a relatively high concentration of water after centre tank fuel scavenge and then, during cold stopover, a very cold water/ice mass accumulated in and around water scavenge inlets (near bottom of main tank), blocking them? As long as no more than 7 gallons of free water was in main tank at any one time, no excess water message would be recorded about this issue.

If each main tank's water scavenge lines became restricted by ice before the return flight, would that also explain how there was a very low level of suspended/entrained water to be found in fuel in main tank as it would not continue to be mixed into the fuel by the water scavenge and tend to separate out?


2. Icing

It almost seems easier to explain icing if there is some form of cascade effect where:

- first, relatively minor icing over time restricts narrower and colder scavenge pipes.
- then, unforeseen major condition such as lack of water scavenge and/or fuel scavenge develops.
- then, unlikely accumulation of free water/ice where it is not expected.
- then, accumulation goes on to cause bigger and worse things downstream.

And has to be readily duplicated on either side. And lack of warning messages and tell-tales such as water ppm accounted for.

[Poof in Boots]

Sorry Lads. Trawling through all these posts and your honest attempts to vindicate the AAIB's preliminary findings, seriously, what are the odds of ice causing both engines to fail at the same time? One I could understand, but not two.

If there was low fuel pressure to the engines caused by a build up of ice, why was this not noticed? Why didn't the PEK/LHR 777 that day also exposed to low temps did not reciprocate the problem. A mate of mine flying a BA 747 at the same time from HKG said fuel temps were in the amber for some time, but no engines stopped.

The fact that this debate continues proves the ice theory is not convincing.

It is something else.

[Re-Heat]

You are seriously trolling.

What are the odds of ice causing both engines to fail at the same time? One I could understand, but not two.
That is the whole point of the investigation

If there was low fuel pressure to the engines caused by a build up of ice, why was this not noticed?
As high fuel flow was not demanded or required until final approach.

Why didn't the PEK/LHR 777 that day also exposed to low temps did not reciprocate the problem.
They don't know, but are probably considering the consequences of two back-to-back sectors in some of the coldest temps recorded for long durations on 777 missions to date.

A mate of mine flying a BA 747 at the same time from HKG said fuel temps were in the amber for some time, but no engines stopped.
Different plane, different route, different design. What is your point?

[Poof in Boots]

Well Re-Heat, many years ago flying back from ANC in very cold weather (-70f+) with US avgas, the main concern then was the fuel waxing, not any water freezing in it.

You would think a newer design aircraft would have better protection against deep cold for long periods. This is not a modern phenomenon.

To lose both engines at such a critical time is unbelievable. I landed 30 minutes before the BA038 but on a GE90 777 from the Gulf and saw it skid to a halt, as we were parked on a bussing stand at the Hatton Cross end of T4 on the opposite side of the runway to where YMMM came to rest.

On our approach quite high amounts of power were required as it was a gusty wind and we were shaken around a bit in our shoulder straps.

[precept]

See following link:

This is a final rule request for comments.

Justia Regulation Tracker Airworthiness Directives: Boeing Model 777-200 and -300 Series Airplanes Equipped with Rolls-Royce Model RB211-TRENT 800 Series Engines, - Federal Aviation Administration - 52909?52911 [E8?21138] (http://regulations.justia.com/view/120567/)

[infrequentflyer789]

It ain't the DFDR recording limitation that just meets or slightly exceeds the regulated requirement, it's the availability of aircraft system sensors and wire routings that sets the actual limit.


I know, and I don't disagree, but the more modern types have moved away from point-to-point wiring to bus-based systems. That allows you to simplify the scarily complex wiring looms (or to do more with the same level of scarily complex). The 777 is ARINC 629 bus, which is multi-transmitter (and more advanced than anything other big jet until you get to 664 / AFDX on the A380 / 787), which should provide a lot of help with this issue.

Best public reference I've got for parameters recorded on a recent jet is for N651AA (flight 965, crashed in columbia). Quoted in various places as recording approx 300 parameters (see eg. Hall's Testimony on March 7, 1996 (http://www.ntsb.gov/speeches/former/hall/jh960307.htm)). That is some way over the minimum (which is still 88 I think).

That flight was a 757 with previous generation (ARNIC 429) bus - so I would expect the wiring on a 777 to be able to route at least that many parameters to the FDR & QAR.


With that said I really don't know what parameters were recorded for BA038Nor do I, and I doubt we'll be told.

[infrequentflyer789]

In this case, the centre tank reduced to a little under 750kg indicated at its lowest at the time of the engines switch to main tank supply, before apparently increasing for some reason by 125kg or so to 800 kg indicated a few minutes later.


The signal is slightly noisy - there are other blips - and that could account for this. Also, consider that when the OJ pumps switch off, does fuel already in the pipes / pump but upstream of the check valve fall back into the tank ? That might be enough to account for this signal.


How localised could that depth of water be given the geometry of the tank, position of ribs and the tank's shape during flight? Can anyone produce a diagram of exactly where everything is at the bottom of the tank near the OJ pump inlets?
I think there have been drawings posted way back in the various threads on this incident - but you'll have to trawl through a lot of posts to find them.


- I note from the rate of scavenge in Figure 1 the rate increased as the level of fuel indicated declined to 0kg. Could that suggest that as the level lowered: the rate of scavenge appeared to increase as less fuel/free water was accessible than expected as it was trapped where the scavenge lines were not working locally; and/or an expected increase given the vagaries and the geometry of tank?
Could be, but I suspect it is more likely a result of the way it's controlled from float valve in main tank - I think the final scavenge rate works out higher than the fuel burn rate when scavenge started.

Yet as a Mad Hatter is drawn to a tea party, I am curious about the possibility given the suggestion in the interim report that air at least might possibly pass through the OJ/jettison check valve (and presumably therefore through the OJ pump when selected OFF too) ...I think that was only if all the main tank inlets were blocked and suction feed woudl pull in either nothing or air from the CT. Nothing vs. air is not a great choice of fuels :uhoh:. Also, if this happens they've found different effects to those recorded on this flight, so it didn't happen in this case.

Overall, I would have thought that the important thing to do with the fuel system FDR data (ie. fig 1 in the report) would be to compare with a similar but incident-free flight. We don't have the data to do that but the AAIB will - I would be very very suprised if this hadn't been done already and anthing unusual in the fuel system data would have been looked into.

[Backoffice]

Whenever I read these posts I get the impression that contributors are talking about free ice floating around in the fuel.
I see this ice, whether it be from water in the fuel or the result of condensation being a sudden release, either due to temperature, flexing of the wing or vibration, of ice which has frozen and adhered to internal wing surfaces during the flight.
i.e. all the scavenge systems, fuel mixers and heaters could never touch this ice as it was attached firmly to a surface and released itself in quantity at roughly the same time, thereby clogging momentarily, the filters to the pumps.

[infrequentflyer789]

Justia Regulation Tracker Airworthiness Directives: Boeing Model 777-200 and -300 Series Airplanes Equipped with Rolls-Royce Model RB211-TRENT 800 Series Engines, - Federal Aviation Administration - 52909?52911 [E8?21138] (http://regulations.justia.com/view/120567/)

Thanks for the link, to quote the AD:

The investigation determined that over a long period of low power
fuel flows and low fuel temperatures associated with cruise flight, ice
can accumulate in the main tank fuel feed system and then release as a
result of increased fuel flow when high thrust is commanded.

Hmmm. Is it me, or does that imply a far greater degree of certainty as to the mechanism than the latest AAIB report did ? I read the AAIB report as saying that this was one icing scenario (of two), that they couldn't reproduce it yet, but it was likely to have happened as it is the only hypothesis they haven't disproved. :confused:

[dxzh]

1. AD

AD pretty much as predicted last week.

As a stop gap measure to keep 777s flying (given regulatory imperative to avoid certain levels of risk for significant failure conditions hazardous to flight), it is definitely to be welcomed though it (almost inevitably due to its immediate nature) misses the opportunity to address some of the likely underlying contributory factors to "hazardous amounts" of ice accumulating in the "main tank fuel feed system".

I would highlight the AD does not reflect:
- the potential build-up of free water and ice in the 200-ER centre tank over two cold-soaked stages.
- the fuel in each main tank remaining cold soaked (together with its scavenge lines) on cold stopover.
- the timing of delivery of any centre tank water into each main tank fuel supply.
- the accretion of ice might not be of the "releasing" type in which case until it fully develops, full flow may not remove it or be affected by it.

In particular, while the in-flight run-up can happen 3 hours before TOD, any ongoing build-up of free water in the centre tank (not addressed by AD) may only be scavenged into the main tanks one hour or two before TOD as on BA038 - if run-up is done before fuel scavenge completed then arguably chain may not be broken unless require another run-up, say, 20 minutes after centre tank indicated as zero?

2. Location of "95%" restriction

If the restriction in each manifold is elsewhere than the "engine fuel" system, as could be suggested from the test rig results which showed significance of a time lag after the accelerations started but before the flow reduced, and operates as an effective restriction on 95% of the cross-section at a point in the "main tank fuel feed" system upstream of the engine, then this AD seems to miss the obvious risk that the restriction was never located in the "engine fuel" system! I assume though that (if I may try and be diplomatic) it is currently expedient to ignore that suggestion.

Ironically, pity the non-RR engined 777 crew and passengers - at least those flying in 777s equipped with RR should now face a reduced risk of icing-induced double rollbacks. Perhaps more risk-averse non-RR 777 operators though might see some advantage in being seen to implement the proposed AD on a voluntary basis, at least pending the next report?

[Chris Scott]

The B777 uses two of just about the most powerful engines in the business, so each engine is presumably fed by some of the largest fuel lines in service.

Strange that this very fuel plumbing may have provided the first recorded example of an engine suffering serious fuel starvation due to a major blockage caused by gradual ice accretion, despite the contents of the fuel tanks being of good quality.

It is suggested that this may have been brought about because the engines were not operated at climb power again after the initial top-of-climb, but at slightly lower (cruise) power settings.

During the last several decades, how many other long-haul jet-transport engine-fuel systems − from those feeding Speys on G2s, through aircraft with engines of ascending fuel flows like (for example) JT3Ds on B707s, DC-8s and C-141s; to CF6s, JT9Ds and RB211s on various aircraft − have been operated successfully at similar altitudes and temperatures to BA038, for similar flight times, often without the application of climb power after initial TOC?

There’s nothing new or particularly unusual in crews avoiding the unnecessary use of climb power when an aeroplane is light.

What’s so special about the B777-Trent? Does anyone find the hypothesis convincing?

[dxzh]

infrequentflyer789 (#1978)

- Agree about noise and switch-off of OJ pumps.

- I have been through posts but not seen centre tank scavenge inlets, OJ pump inlets or drain valves relative to each other or side on view as to how far off floor. Of few pictures have seen, they include:
Sumping - http://panchromat.org/.misc/B777-docs/auto_sumping_typical_installation.jpg
Vent picture - http://panchromat.org/.misc/B777-docs/typical_Boeing_vent_system.jpg
Pump - http://panchromat.org/.misc/B777-docs/typical_boost_pump_or_ord_jett_pump_installation.jpg
Centre tank - http://www.pprune.org/3929959-post284.html
Engine fuel supply – ImageShack - Hosting :: 777engineug1.jpg (http://img442.imageshack.us/my.php?image=777engineug1.jpg)
RR Trent parameters - http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/b443906400b2f413862572a4006eb74e/$FILE/E00050EN.pdf
Plan of fuel supply: ImageShack - Hosting :: 777fuelpw3.jpg (http://img260.imageshack.us/my.php?image=777fuelpw3.jpg)

- Agree re burn rate - slight difference in main tank flow rate just before and then after scavenge finishes.

- Agree re context of remark in AAIB report - my point was more that it seemed to suggest if gas then why not fluid could move through inactive OJ pump with suitable pressure differential? [I had an obscure "March Hare" theory a few posts back that air might be dissolved/entrained into main tank fuel as result of operation of centre tank fuel scavenge when CWT dry and as a result (i) subsequent release of undissolved air from air-saturated fuel into suction feed pipe and/or fuel manifold near OJ/ jettison check valve [or, before cavitation (as cause) ruled out, in HP pump] and (ii) so suction feed restricted by undissolved air and/or undissolved air near OJ/ jettison check valve end might allow localised low pressure fluctuations induced by cycling to result in OJ/ jettison check valve opening if surge of pressure in centre tank on fast descent, thereby introducing water slug (not air) to fuel manifold. In my dream world both the Mad Hatter and March Hare were coming to tea.]

- Agree that will have compared fuel data and that of previous flight.

Anyway it seems there is still quite a bit of Boeing testing to be done on the cascade of contributory factors leading to the location of the 95% restriction in the underlying fuel system, and the tentative, conflicting scenarios to date.

Perhaps the expense of putting a bit more flight test kit where not normally found in tanks and supply lines of a real plane (with correct geometry) and then flying it would be worth it (maybe could add water to centre tank and lower the temp of fuel in one of the main tank before uplifting it to cut to the chase, etc) ... since a double rollback is not just unusual but after all a surprisingly serious failure condition in an otherwise excellent aircraft.

[Green-dot]

As posted by infrequentflyer789:
The 777 is ARINC 629 bus, which is multi-transmitter (and more advanced than anything other big jet until you get to 664 / AFDX on the A380 / 787), which should provide a lot of help with this issue.


The 777 FDR receives and stores selected parameters from various systems and sensors (to know which parameters must be equivalent to drawing Excalibur from the stone). A digital flight data acquisition function (DFDAF), part of the airplane information management system (AIMS) receives all the flight recorder data. The data from the systems is received through ARINC 429 and ARINC 629 data buses, and also analog signals and analog discretes. The DFDAF processes this data (converts it to a digital format) and sends it to the FDR through ARINC 717 data buses.



As posted by Backoffice:
I see this ice, whether it be from water in the fuel or the result of condensation being a sudden release, either due to temperature, flexing of the wing or vibration, of ice which has frozen and adhered to internal wing surfaces during the flight.


Most likely (if water sumping was correctly performed) there would not be that much ice adhering to the internal wing structure after a 20 hour downtime with temperatures between +6C and +11C before the flight to Beijing on Jan. 16. Add to that the 2 day maintenance downtime (inside a hangar?) before the flight to/from Shanghai on Jan. 14-15, where likely water draining and refueling would have taken place only hours before departure to Shanghai. Outside temperatures at Heathrow were between +4C and +11C on Jan. 12 thru 17.

It seems to me that whatever amount of water was present in the tanks during this period with ground times of 48 hours and 20 hours respectively, most of it, if present, would have been drained. In addition, refueling at Heathrow (according to the AAIB) occurred only after sumping for water, any condensation adhering to the interior structure (water, not ice with so many hours of temps. well above freezing) would have been absorbed by the fuel during refueling and would not have had time to settle at the bottom of the tanks before the flights took place.


As posted by Chriss Scott:
What’s so special about the B777-Trent? Does anyone find the hypothesis convincing?


Apart from the Trent being different from the other engines types, the plumbing in the airplane fuel system is no different then for the other engine types, except for the engine/fuel system plumbing interface.

No, i do not find the hypothesis convincing, especially when the weather conditions and actions taken to drain water while on the ground for considerable times at Heathrow are taken into account.



Green-dot

[Feathers McGraw]

Chris Scott wrote:

"The B777 uses two of just about the most powerful engines in the business, so each engine is presumably fed by some of the largest fuel lines in service.

Strange that this very fuel plumbing may have provided the first recorded example of an engine suffering serious fuel starvation due to a major blockage caused by gradual ice accretion, despite the contents of the fuel tanks being of good quality."

Well, if you think about it, having a larger diameter pipe to allow higher flow at full power means that the effects of low power and fuel flow for long periods are exacerbated, the fuel is moving more slowly because a given volume travels more slowly through a larger diameter pipe. Hence, if this is down to ice accretion on the pipe walls, there is more time for an ice crystal passing accreted ice to stick to it.

[Old Engineer]

dxzh, in re your post #1969 of yesterday, on page 99:


Is it a red herring even to contemplate the boost pumps or centre tank pumps allowing the passage of fuel/water when they are selected OFF? I guess the premise of the suction feed test on the ground (as a pure test of the suction feed) would be flawed if it was a possibility that an engine-driven LP could draw fuel through any of the unpowered pumps from centre tank - and thus I would like to discount the idea completely. Yet as a Mad Hatter is drawn to a tea party, I am curious about the possibility given the suggestion in the interim report that air at least might possibly pass through the OJ/jettison check valve (and presumably therefore through the OJ pump when selected OFF too) ...


Centrifugal pumps of conventional design can be operated in series; I have done design work with such arrangements. It does not matter if the upstream pump (in this case) loses its electrical power. There are no in-built internal obstructions to continued flow through a centrifugal pump whether or not its impeller is still free to turn, or siezed in its bearings.

It is conceivable that the housing of such a pump could be fitted with a stop valve held open by a solenoid energized by current from the pump power circuit. I haven't seen any indication that the 777 pumps of which I have details (Eaton Aerospace (UK) wing tank LP boost) have any such feature. This seems undesirable in an aircraft, just my opinion. I've seen systems (non-aircraft) that had such a feature, but only as a separate valve in the piping.

As to air entering the engine LP pump suction, I can only address the fuel path from the main wing tanks. Here the wing tank suction points are above the engine fuel feed in such a way that the engine LP pump would normally operate with a gravity-flooded suction if fed entirely from the wing on that side, with the LP boost pumps of that side off. I can't say I see this as even remotely likely in the air, and use it only by way of example (lacking as yet sufficient info regarding elevations in the center tank plumbing).

Anyway, with a fuel velocity of at most 7 feet per second (8 possibly), I cannot see it likely that significant air would be entrained should the suction of one of the wing LP boost pumps become unflooded itself due to fuel slosh. It isn't like the engine pump was above the fuel source. BTW, the velocity given is for a fuel rate of 35,000 lbs/hr. This is the conventional maximum velocity (for avoiding static charge on the fuel), and may also be seen from the near 2" discharge diameter of the wing LP boost pump casting.

The same principles would apply to the center tanks, but as noted I don't know the elevations of the various components clearly enough to comment. The dimensional detail of the wing LP boost pumps in on the Eaton Aerospace website; earlier I forgot to mention that it is not in the brochures-- instead look under "downloads" for the data sheets, including B777-300 for a comparison to the -200.

Following what I consider to be good example, I stand to be corrected in this matter if necessary. Well, it is a somewhat complex fuel system, although I think it is robust, simple in components and backup/bypass paths, and extremely reliable, at least until now.

OE

[cwatters]

Quote: All of the testing and research of this accident has been conducted
on Boeing Model 777-200 and -300 series airplanes, equipped with Rolls-
Royce Model RB211-TRENT 800 series engines. Initial review of 777 other
airplane engine combinations has not revealed the same vulnerability to
the identified unsafe condition. End Quote.


Sounds like they are reasonably sure where the blockage occured and its somewhere specific to airframes plumbed for RR engines. Why wouldn't a similar release of ice be a hazard to other engines?

Edit: I was asked to post the source of the above quote. It came from this document posted earlier in this thread by "Precept"...

http://www.pprune.org/4391725-post1975.html

Justia Regulation Tracker Airworthiness Directives: Boeing Model 777-200 and -300 Series Airplanes Equipped with Rolls-Royce Model RB211-TRENT 800 Series Engines, - Federal Aviation Administration - 52909?52911 [E8?21138] (http://regulations.justia.com/view/120567/)

[lomapaseo]

cwatters
Quote: All of the testing and research of this accident has been conducted
on Boeing Model 777-200 and -300 series airplanes, equipped with Rolls-
Royce Model RB211-TRENT 800 series engines. Initial review of 777 other
airplane engine combinations has not revealed the same vulnerability to
the identified unsafe condition. End Quote.


Sounds like they are reasonably sure where the blockage occured and its somewhere specific to airframes plumbed for RR engines. Why wouldn't a similar release of ice be a hazard to other engines?

please identify source of quote that you used in your post

[archae86]

Initial review of 777 other airplane engine combinations has not revealed the same vulnerability to the identified unsafe condition.
Regarding the above quotation, Google is your friend, and finds that exact string at:

FR Doc E8-21138 (http://edocket.access.gpo.gov/2008/E8-21138.htm)

Assuming this site to be legitimate (I think it is), it comes from the discussion portion of the Supplementary Information section for the AD being promulgated by the FAA in response to the incident which is the subject of this thread.

[phil gollin]

This FAA AD (for comment) amazes me - to put it mildly !

It would seem that whilst the lead autority (the AAIB) cannot assess what has happened and only speculates - the FAA SEEMS to have decided what happened, and more importantly that it couldn't happen to other engines on 777s ? (The AAIB thinks proper testing of other engine/airframe combinations are required).

Well - IF the FAA know it can't happen to other engines, maybe they can tell us (and the AAIB) what happened with the Trent supplies.

PLEASE can someone explain, as this doesn't make any sense to me.

.

[gas path]

Part 'g' has been written (in beta form if you like ;)) for the AMM and is awaiting final approval. It has been tried and tested mainly to see if any improvements can be made (for example reducing the number of trips between the flt. deck and refuel panel) or whether it's a one or two person operation!
As regards the comment 'it can only happen to a RR Trent powered a/c' may stem from the fact that all the fuel system components are on the outside of the fan case. Whereas certainly for the GE90, all the components are around the core engine in a very warm environment. Other than the pylon area the airframe fuel system is identical. :8

[BlueRay]

what if the sumping was not done? For example the engineer just rubber stamped the job. I've heard it goes on. Now the aircraft has the free water thats needed to create the ice that caused the blockage that brought the craft down prematurely.

Just a thought;-)

[Dairyground]

About ten pages back, there seemed to be an emerging consensus that the reason the RR engine was being singled out for changes in operating procedures was the presence/position/design of the FOHE. If blocking of the heat exchanger was the immediate cause of the loss of power, then the time between the demand for increased thrust and the start of uncommanded power reduction could give an indication of where in the system the ice came from. I could dig out the time from the AAIB report, but I have no information on the speed of fuel flows or the geometry of the pipework. Does anyone in possession of the relevant information care to do the sums?

[cwatters]

Re: http://www.pprune.org/4392955-post1983.html

If refueling was done after sumping at LHR what about the possibility of contaminated fuel being loaded at LRH? Unlikely, but if I understand correctly they had a water alert at LHR? Say that water was correctly scavanged and sent to the engines causing a layer to build up in the plumbing (not enough to cause a problem in itself). The contaminated fuel would have been used up and replaced with good fuel in china. It was cold there so ice in plumbing (if not the tanks) might have remained frozen? Then on way back ice build up reduces until the last bit brakes off in chunks and causes the serious restriction. Result no water detected in the tanks.

[Green-dot]

However unlikely (it had crossed my mind as well), it could be a possibility but the AAIB most likely will have investigated such a scenario. Fuel in storage tanks, fuel hydrants and/or bowsers are also monitored for contamination and records are kept. If there would have been a contaminated batch of fuel originating from LHR, I'd suspect more aircraft would have been affected.

I know, it is quite speculative to say the AAIB will have investigated because none of their reports have confirmed that they did but knowing their thorough investigative track record, my guess is that they did.

Regarding the water alert, none of the AAIB reports sofar have confirmed the claim of a water alert for any of the flights referred to in these reports. I am sure that if it was an issue it would have surfaced in the most recent interim report.


Green-dot

[sky9]

I flew the 767 some years ago, I seem to remember that there weren't any water drains on that aircraft. Does the 777 have them?

[Desk Jockey]

"I flew the 767 some years ago, I seem to remember that there weren't any water drains on that aircraft. Does the 777 have them?"

They both do.

[BlueRay]

of course 767 has water drains! All aircraft do

[Obie]

I really don't think sky9 meant what he said!

As an ex 767 driver, he's obviously no fool!

Some editing required perhaps?

[Green-dot]

Any chance there is a correlation in progress between the investigation authorities with respect to the BA38 and QF72 events regarding possible uncommanded system behaviour?


Green-dot

[BlueRay]

Simple answer NO! BA038 was brought down due to ICE in the fuel system. Nothing more nothing less.

[draughtsman99]

Simple answer NO! BA038 was brought down due to ICE in the fuel system. Nothing more nothing less.

Must be great to be so sure in your own mind - do you work for London Airways (BA)

[BlueRay]

Draughtsman, its not about being clear in ones mind, just read the AAIB report. Just they can't fathom were the water came from. Of course the answer is sure to be revealed in the near future.

I like your continual reference to London AIrways, maybe this should be a new thread. Is BA entitled to continue using British in their name when they have pulled out of all regional bases?

I guess you work for them out of GLA, sad day for you all. Lets hope your MP Sheridan and his motion in Parliament brings about a U turn.

Back on thread, ice brought down BA038, the Qantas flight cause is as yet unknown and totally unconnected.

[Green-dot]

I have read all the reports.

Ice accumulation is a hypothesis, nothing more.

No more than "backdoor coupling."



Green-dot

[777fly]

Winter is upon us, so maybe we will see a repetition of BA 038. But then, maybe not. I have flown BA038's profile before without mishap, so why did that accident happen just once?

I do not support the fuel icing scenario. I reaffirm my hypothesis that on BA038's flight the fuel uplifted in Beijing had an unusually high gas content. This excess gas became trapped in the suction feed pickup in the wing tanks during flight, was pressurised in the descent (above normal levels) and was later injected into the fuel manifold at low altitude, as the trapped gas exceeded LP pump output pressure. The ejected gas restricted fuel flow to both engines (almost) simultaneously.

[India Four Two]

On one of my infrequent visits to Heathrow last week, I saw what I presume is G-YMMM sitting behind screens not far from its original location on the threshold of 27L.

Can someone tell me why the fin has been removed? A source of spare parts or an obstruction issue?

[overstress]

I can think of 2 better reasons. Firstly it was a gigantic vertical reminder of the event to those not fortunate enough to be armchair theorists on PPRuNe, secondly in high winds the ac was getting blown about.

[gas path]

Can someone tell me why the fin has been removed? A source of spare parts or an obstruction issue?
The fin was removed at the request of the A/C's owners (owned by the insurance co. and NOT BA.), for sale to anyone that wants to buy it! Plus as overstress points out the a/c was moving about as its no longer supported on jacks but lying on 'sleepers'.

[BGQ]

It is my understanding that one of the main differences between the Trent engine installation and others is the design of the FOHE and the position it is plumbed on the trent. Perhaps one of our engineering buddies can confirm what the difference is.

[Swedish Steve]

It is my understanding that one of the main differences between the Trent engine installation and others is the design of the FOHE and the position it is plumbed on the trent.
Yes. On the Trent, the Fuel passes through the FOHE first when it enters the engine. So there is a chance that any ice could block the passages in the heat exchanger. In the GE the fuel goes through the pumps first, so there is good chance that any ice will be broken up in the pump.

[FlyGooseFly!]

I'm still very unhappy with all the findings so far and have little confidence in the ice theory.

This feeling will remain until a fully rigged 777 can be sat in a cold store to exactly similate the flight and bring about the same engine problems a number of times just like any other proper scientific experiment - demonstrable by REPEATABLE experiment.

Until then I shall habour deep suspicions that some dark conflict lies buried in the software with sharp teeth waiting to bite some other poor souls when they least expect it.

[Selfloading]

http://www.pprune.org/data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABwAAAAOCAYAAAA8E3wEAAAAB mJLR0QA/wD/AP+gvaeTAAAACXBIWXMAAAsTAAALEwEAmpwYAAAAB3RJTUUH1QUUDyoqJjAq RwAAAN1JREFUOMu1lMkVwyAMBYe0JGpCNUFNVk3k4AUwxPGS+ILxkzX8jyTH/Sfu9nrmJ3cXlnMASyWRPwd2d5XlHCBZn1BthcbRAdxTZQDI8k3mQzg11rhF+ QZ9jdNOcQib6GFQYJYgCFucSRf6GsLU6wEY5yubTFqF2yq1vRwr3INXdQUWG +je1pELX4ED1wDyRAR0WfuAA9gloITyvsFMIMgYInYRqF6rO9Sqz9qkO5ily o0o3YBwJ+6vrdQonxWUQllhXeHcb/wabMPkP2n81ocAIoLZrMqn/4y2RwP8DcQ+d6rT9ATiAAAAAElFTkSuQmCC

Until then I shall habour deep suspicions that some dark conflict lies buried in the software with sharp teeth waiting to bite some other poor souls when they least expect it.http://www.pprune.org/data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABwAAAAOCAYAAAA8E3wEAAAAB mJLR0QA/wD/AP+gvaeTAAAACXBIWXMAAAsTAAALEwEAmpwYAAAAB3RJTUUH1QUUDyoqJjAq RwAAAN1JREFUOMu1lMkVwyAMBYe0JGpCNUFNVk3k4AUwxPGS+ILxkzX8jyTH/Sfu9nrmJ3cXlnMASyWRPwd2d5XlHCBZn1BthcbRAdxTZQDI8k3mQzg11rhF+ QZ9jdNOcQib6GFQYJYgCFucSRf6GsLU6wEY5yubTFqF2yq1vRwr3INXdQUWG +je1pELX4ED1wDyRAR0WfuAA9gloITyvsFMIMgYInYRqF6rO9Sqz9qkO5ily o0o3YBwJ+6vrdQonxWUQllhXeHcb/wabMPkP2n81ocAIoLZrMqn/4y2RwP8DcQ+d6rT9ATiAAAAAElFTkSuQmCC



You believe a software problem caused cavitation in the fuel pumps?
and what stopped the engines spooling up when the pilots advanced the throttles, isn't it a mechanical linkage in the 777?

[Smilin_Ed]

I've read all the previous 2012 posts. Unless I missed something, it has been conclusively shown that the fuel metering valves moved to the full open position but there was no fuel to move through them. Since the valves opened, how could it be a software problem? The system responded to the movement of the throttles. The engines failed because of a scarcity of burnable materials to pass through that system. :ugh:

[Phlap1]

This accident will eventually fall into the same category as the 747
centre wing tank saga. An accident or two followed by speculation
and investigation over many years. There is obviously a design
fault that could recur. But economic expediency by airlines, boeing
and the engine manufacturers means we all take a calculated risk
until the real problem is fixed. My bet is a small mod will be made
to the fuel system, a proceedure change to fuel management etc.
Just as the 747 problem unfolded, they will not acknowledge a
known design fault but will piecemeal create a fix. Why did they
change the centre wing pumps on the 747, why have they built
a nitrogen enrichment system into the latest 747s centre tank.
Different technically, but identical legally. I guess its all part
of human progress, we learn as we evolve, build technology.

[Chris Scott]

Quote from Swedish Steve:
On the Trent, the Fuel passes through the FOHE first when it enters the engine. So there is a chance that any ice could block the passages in the heat exchanger. In the GE the fuel goes through the pumps first, so there is good chance that any ice will be broken up in the pump.

If memory serves, that's news on this thread. If relevant, would it be practicable to re-position the FOHE, Steve? If so, would you expect the mod to be in the pipeline already (pun not intended).

Quote from Phlap1:
Just as the 747 problem unfolded, they will not acknowledge a known design fault but will piecemeal create a fix.
[Unquote]
In the event of that being necessary, let's hope they don't hang about too long in an effort to avoid it being too obvious to potential litigants. If they did, they could end up wasting one of the luckiest breaks in aviation history.

Quote from Smilin Ed:
...it has been conclusively shown that the fuel metering valves moved to the full open position but there was no fuel to move through them. Since the valves opened, how could it be a software problem?
[Unquote]
Looking at hypothetical software problems, could the fact that the position sensors indicated and recorded the valves fully open not be part of it?

Quote from Smilin Ed:
...the fuel metering valves moved to the full open position but there was no fuel to move through them.
[Unquote]
Considering a given engine: if the valve was indeed fully open, there was certainly a flow restriction elsewhere, as you say. Was that due to a foreign-object blockage (ice, for example), a loss of pressure (and/or suction) to shift it through, or the anomalous closure of another valve?

Quote from Smilin Ed:
I've read [U]all the previous 2012 posts. Unless I missed something...
[Unquote]
Well... There's a thought. ;)

[Smilin_Ed]

Quote from Chris Scott
Quote from Smilin Ed:
...it has been conclusively shown that the fuel metering valves moved to the full open position but there was no fuel to move through them. Since the valves opened, how could it be a software problem?
[Unquote]
Looking at hypothetical software problems, could the fact that the position sensors indicated and recorded the valves fully open not be part of it?
Wouldn't the software which moves the fuel metering valves be different from the flight recorder software which monitors the valve position? Surely they are independent. Is there someone here who can answer that?

[Walnut]

I believe Swedish Steve may have stumbled on the answer.

If the fuel flow through the FOHE became more & more partially blocked throughout this long cold flt,then a continuous descent at low pwr would not have changed anything, until more fuel was required at engine spool up at 1000ft. Then the ice would be sucked further into the FOHE causing a blockage, it would have melted with time but time was not what they had.
This in fact could explain the cavitation damage of the pumps, it had been happening to a lesser scale on other flts but the temporary "hicups" had not been noticed.

This had been a long very cold flt, with maybe a marginal fuel spec.

[davidash]

It seems incredible to me that where there has been an obvious fault in an aircraft type whole fleets have been grounded until the problem is fixed or checked. Here we have a heavy, sophisticated aircraft that crashes for no expiclable reason and it just keeps on flying until, perhaps, it happens again! Can you imagine what must go through the mind of every 777 aircrew on finals? Surely the aviation authorities can do better than this or do we have the dreaded economic considerations outweighing the value of human lives?

[stilton]

Being inherently distrustful of computers I will always suspect 'wonky' software.

But just in case, why did we as Pilots accept losing total control of the fuel heat ?

From the 75 onward on Boeings (don't know about Airbus) not only do we have no control of such, but not even a way of monitoring its activation.

Bring back fuel heat switches !!

[HotDog]

Bring back fuel heat switches !!

And flight engineers to use them as necessary!

[phil gollin]

I do NOT want to be too dogmatic as it has been so long since this (and the previous) thread started to remember all the details, let alone theories.

However, If I remember correctly, the engine thrust was increased and decreased several times during descent without problems. In addition, the actual problems occured at slightly different times but ended up at almost exactly the same amout of (lack of) thrust. It seems almost impossible that the conditions in each tank were such that the "icing" (OR WHATEVER) acted at different times but ended up with the almost exactly the same results.

People grasped at the cavitation damage because IF (AND IT IS A BIG IF) the cavitation meant that pumps would work at x% capacity and this would show why the thrust fell to the levels that actually concerned. HOWEVER, as no definitive statements accompanied the last AAIB report it is questionable as to whether this is possible, or not.

It seems odd that nothing has arisen in the more than 9 months since the accident (and especially since the Northern Hemisphere Winter is near enough here) to actually guide airlines in possible ways to minimise a re-occurance of such an incident.

(Sorry for the CAPITALS - but people do have a tendency to go off on tangents if you don't spell things out).

.