BA038 (B777) Thread [Archive] - Page 6

snanceki

4th Jun 2008, 06:11

Airfoilmod: We are still stuck with a philosophical foundation to the engineering. How do TWO separate, isolated and independently controlled systems exhibit virtually identical (Failure) behaviour simultaneously.

Please don't overlook the FACT that FUEL, ENVIRONMENT and PROCEDURES are common to both installations.

Why do you assume FAILURE?

It is quite possible that no FAULT (i.e. DEFECT) occurred in the homologated imstalation. Just that operating parameters (possibly even STANDARDS) were (are) inadequately specified.
I suspect that fuel QUALITY is a "Black Art" and to a large extent relies on standardised manufacturing process to control various aspects of quality.

Since the initial AAIB report I have been concerned regarding the low fuel freezing point on the sample taken from BA038. It sticks out like a sore thumb!
Maybe some of you guys can provide DATA on what the expected RANGE of this parameter is. If, as I suspect, the range is normally in the order of +/- 5 degC from whatever is the agreed "norm" is, then what made this fuel have such a spectacularly different freezing point?? OR is this very low freezing point understood, and simply a red herring?

The fuel may be "in spec" but something was unusual IMHO about the sample(s?) measured.

Whether this unusually low freezing point was due to something linked to the original fuel processing / additives or whether it was the result of some strange in flight stratification process remains IMHO an OPEN question.
Even if the low freezing point itself is not an issue maybe it highlights (indicates) a fuel with a greater propensity to cause cavitation or whatever.,

A reason exists for this near disaster! With all the data that exists I find it almost incredible to accept that a (potential) cause / sequence of events has not been identified.

OK it may take time to CONFIRM any such potential sequence of events but although we are struggling with inadequate data I'm convinced that this cannot be the case for the investigators.

However, the part of this that I don't understand is why no activity has occurred to put in place more rigorous procedures at least till the sequence of events is published. e.g. Tightening of fuel min temp or whatever.

So maybe the cause is understood and since the RISK of a repeat event is considered LOW there is no need to rush out a further report especially if this is POLITICALLY SENSITIVE in someway.

All will become clear in the fullness of time!

cwatters

4th Jun 2008, 06:27

This has Min (-78F), Max (-42F) and Average (-53F) for 19 jet fuels in the USA in 2005...
http://pps.ms.northropgrumman.com/aviation.htm

snanceki

4th Jun 2008, 10:17

Hi,
Thanks for that report.

I assume these were all tests on supposedly the SAME type of fuel (Jet A1 or whatever it might be called in the USA).

The report doesn't indicate the specification limits nor the expected range limits for most samples.
So were these 19 samples in spec?

Differences look considerable. So why such differences?
This supports my fuel quality is a "Black Art" proposition.

I wonder why vapour pressure, calorific value etc wasn't (aren't) checked?

If I was buying aviation fuel in vast quantities I would want to be sure that the stuff wasn't being "diluted" or in other words providing less bang (mpg in car speak) for my buck.

Interesting.

chris weston

4th Jun 2008, 10:20

Snanceki sir, I very much agree that the evidence so far points to it being a fuel related event.

Without going over old ground too much, suffice to say that if we have an abnormally low fpt, and this fuel seems to have had just such, the lower intermolecular bonding levels that allow this fpt will also make for a correspondingly increased propensity for the fuel to go gas phase in the HP pumps - ie to cause cavitation when the FADECs commanded an increase in fuel flow rate at circa 700 feet.

A proper statistical picture of evidence of cavitation damage in other 777s would be very useful and I bet Boeing/RR have looked at this, hard. It could be more of a problem than is realised with all specs/SOPs et al on 038 being met with the unforeseen until now problem built in.

I have deliberately omitted further comments on additives and stratification.

Much respect from me for the chaps on the flight deck that day

CW

snanceki

4th Jun 2008, 13:48

Chris Weston

You appear to be in agreement with my position.

i.e. Looks like a "standards" / design parameter issue.

airfoilmod

4th Jun 2008, 14:07

Good Morning, Sir- Very difficult to read for understanding on the Net. I like to hear and see while discussing, old pilot. Your purpose in quoting my rhetorical question isn't clear to me. I must say though that the rest of your post describes my conclusions quite well, such as they are. My Bottom Line in this has to do with ETOPS. This isn't a generic incident for me. I get from your concerns that you may share my view. Without being specific, I believe that mitigating alterations to procedures have been created. I know of a few and believe that there are sufficient changes to protect the domain of Twin flight. Some are mentioned on this Thread, as well as other places, some are proprietary. To repeat something I wrote in February, just because one isn't directly aware of solutions doesn't mean they don't exist and haven't been engaged. To think in a fearful way that because AAIB haven't released a report sufficient to please all the interested public and somehow there is an unknown danger afoot is silly.
I have perfect faith in flying and in ETOPS.

BRGDS Airfoil

chris weston

4th Jun 2008, 17:59

Snanceki you are correct, that is my basic view too.

But as ever, the devil is in the detail and for that we must wait.

I have unequivocal respect for AAIB too.

CW

Mariner9

4th Jun 2008, 18:51

:mad::ugh::ugh::mad:

Someone above published a survey undertaken by Grumman. It confirmed what I (and some others) have been saying from the start - namely that the formulations of jet fuels vary hugely depending on crude source, production process (eg hydrotreated, severly hydrotreated etc) additives used etc etc etc. The above list does all meet spec by the way. But for commercial privilege, I could publish a list of a few thousand jet samples, several hundred or so of which are off spec for a variety of parameters (but the high proportion of off spec results is not surprising given that I investigate Jet contaminations for a living)

The reported freezepoint for the subject fuel falls within the limited sample range (19 samples?) in the Grumman list - it was ABSOLTUELY TYPICAL of the value you'd expect to see. If low freeze points were a problem, Defstan/ASTM specs would specify a range of acceptable freeze points not just a maximum. So please, do not continually harp on that at the FP was lower than it should be - it was not.

Few other pointers from preceding few posts:

Vapour pressure: This depends very much on fuel temperature. The lower the fuel temp, the lower the vapour pressure. If the fuel had an abnormally high vapour pressure the problem would have arisen during highest fuel flow rate and highest fuel temperatures - which would have been at takeoff. In any event, if the vapour pressure was too high, it would have been off spec on flashpoint (which it apparently wasn't)

Cal val: If cal val of the fuel was insufficient to provide sufficient thrust to arrest descent, how the heck could the a/c take off in the 1st place? In any event, Specific Energy forms part of the spec, and there is no indication that this parameter was off spec.

Additives: The allowed additive list for Jet A-1 is very restrictive, and additives used must be stated on QC's. If excess or unauthorised addives were used, it would have been picked up on GCMS.

Another point: Various people have talked about stratification. If the fuel had stratified, and the "good" components been consumed during the cruise leaving only "bad" stuff (technical terms :ok:)- this would have been plainly evident to the AAIB by simple comparison of the measured quality parameters of the remaining fuel with the reported quality parameters of the supplied fuel. There is no suggestion in the AAIB reports that fuel quality differed significantly than certified at loadport.

Edited to improve the English (originally typed upon return from the pub ;))

snanceki

5th Jun 2008, 05:12

Hi Mariner9,
So you are a Jet fuel "expert". Excellent.

If your job is Jet fuel compliance then this suggests that fuel quality is important although I have no knowledge of what parameters in the fuel may be of greatest concern and why. Maybe you could enlighten us.
What is the most common cause of non compliance?
What causes this non compliance?
Why is this deemed a concern?
Incidentally what happens to fuel that doesn't meet spec?

I suggest that you missed my point.
I did not intend to convey that the fuel in the subject aircraft was substandard in some way (the AAIB appear to have eliminated this by stating that the fuel was "in spec") but merely pointed out that ACCEPTABLE "quality" appears to have a wide range.

I certainly didn't suggest that the fuel was "so bad" that it wouldn't burn, for the reason you pointed out (would have been determined during take off/climb) but since Cal value = heat from fuel = Thrust, a lower cal value will give you less "bang for your buck".

HOWEVER, this wide range of acceptable quality MAY.... in some yet to be determined way..... have been implicated in the chain of events that occurred to BA038.

SOMETHING caused this incident.

As I stated I suspect we are talking about STANDARDS / SPECIFICATION /PROCEDURE boundaries in some way, otherwise the cause would have been determined by now.

snanceki

5th Jun 2008, 05:37

Airfoilmod. How do TWO separate, isolated and independently controlled systems exhibit virtually identical (Failure) behaviour simultaneously.

Good morning.
I quoted your rhetorical question since I believe the answer lies in something that is COMMON to the two separate, isolated and independently controlled systems.

ETOPS, from my extremely limited knowledge of the subject, appears to be working well, but we should not overlook that fact that certain aspects of the (duplicated) installation are COMMON.

It appears that we may not be looking at something having gone wrong, but rather a situation where the interface between
FUEL, ENVIRONMENT, DESIGN, STANDARDS and PROCEDURES has created an UNFORSEEN situation / scenario.

FullWings

5th Jun 2008, 10:21

From reading the AAIB reports, it would seem every component they've tested so far does/has work(ed) according to design parameters. This includes the integrity of the fuel supply system from both tanks.

We have symptoms of fuel starvation to the power units, cavitation damage to the engine pumps, tanks pumps still running (no pressure warnings) and plenty of fuel in the tanks: logically, this points to some restriction between the tank pumps and engine pumps. So far, nothing has been found, so the restriction appears to have been temporary in nature. I presume a lot of time is being spent trying to figure out what this might have been, especially as it affected both L & R systems almost simultaneously.

We're down to contaminant (nothing significant found yet), odd fuel behaviour (ditto), physical change to fuel lines to reduce cross-sectional area (no evidence for this at the moment) and ??

I'm hoping something might come from a detailed environmental test of the fuel supply chain - no news yet...

Smilin_Ed

5th Jun 2008, 10:30

Quoting snanecki, "If, as I suspect, the range is normally in the order of +/- 5 degC from whatever is the agreed "norm" is, then what made this fuel have such a spectacularly different freezing point?? OR is this very low freezing point understood, and simply a red herring?"

Right on snanecki! I tried to say this earlier but couldn't bring up the words that you have. :ugh:

Mariner9

5th Jun 2008, 11:38

If your job is Jet fuel compliance then this suggests that fuel quality is important although I have no knowledge of what parameters in the fuel may be of greatest concern and why. Maybe you could enlighten us.
What is the most common cause of non compliance?
What causes this non compliance?
Why is this deemed a concern?
Incidentally what happens to fuel that doesn't meet spec?

My job is not routine compliance testing (though it was a decade :{or so ago), we only get involved once problems are identified.

Perhaps not surprisingly, the most frequent problem by far in Jet fuel is failure of the simplest test available - visual appearance, where the spec is "Clear, bright, and visually free from solid matter and undissolved water at ambient temperature". Generally, this problem can be solved by simple filtration. In extreme cases, the fuel is downgraded to regular kero or blended into gasoil.

Another common problem is flashpoint, particularly if the fuel is transported at sea after a previous low flash cargo. Reduced flashpoints are very difficult to resolve, necessary blend ratios are impractically large. Typically, the most economical action can be to re-refine the material, but that will always pose production problems to a refinery that is probably already maximising Jet output - additional kero in the crude stream will reduce output of gasoil and gasoline.

An interesting one, and possibly of relevance to BA038, is particulate contamination. This is measured by filtering some fuel, and weighing the particulates collected. An associated test (which forms part of the military spec) is filtration time, which specifies the minimum time for 1 US gallon to be vacuum-filtered. We have had numerous problems where anti-icing additives have been incompletely mixed, which for reasons we dont fully understand, cause difficulties in filtration. Obviously, filtration difficulties would impact on the flow of fuel through aircraft filters, and I would imagine that the effect would worsen with decreasing temperture. However, I have no idea if the subject fuel contained any FSII - chances are it didn't. I also don't know if the AAIB have had particulate contamination/filtration time checked as strictly speaking, the limits only apply at the point of manufacture. It would seem unlikely that they haven't checked this basic point however.

The remaining common failure is the JFTOT (Jet fuel Thermal Oxidation tester"). This arises where the fuel storage or transportation includes incompatible metals such as copper. It can generally be treated by the addition of approved metal de-activator additives to the fuel.

I suggest that you missed my point.

I didn't, but concede that I didn't answer it properly!

I did not intend to convey that the fuel in the subject aircraft was substandard in some way (the AAIB appear to have eliminated this by stating that the fuel was "in spec") but merely pointed out that ACCEPTABLE "quality" appears to have a wide range.

I certainly didn't suggest that the fuel was "so bad" that it wouldn't burn, for the reason you pointed out (would have been determined during take off/climb) but since Cal value = heat from fuel = Thrust, a lower cal value will give you less "bang for your buck".

HOWEVER, this wide range of acceptable quality MAY.... in some yet to be determined way..... have been implicated in the chain of events that occurred to BA038.

As I stated I suspect we are talking about STANDARDS / SPECIFICATION /PROCEDURE boundaries in some way, otherwise the cause would have been determined by now.

Briefly dealing with the "bang for buck" point first, the answer I give below should hopefully answer the main query posed by you and others, which I interpret as "even though the fuel meets spec, could the wide range allow the presence of unsuitable components that wont burn properly"

Specific energy for Jet is specified at minimum 42.8 MJ/Kg. However, it does not have to be measured. Instead, it is acceptable to calculate the specific energy based on certain measured quality parameters (density, distillation recovery temperatures, aromatics content, and sulphur content). This shows that the authorities consider it reasonable and safe to conclude that a fuel which meets spec for those key parameters must produce sufficient energy, even if the material is not wholly "kerosene". Rest assured, this has been based on years of research and analysis. Clearly, they do not consider that other materials with similar parameters but adverse energy characteristics could be substituted. In any event, other burning characteristics of the fuel such as smoke point are checked.

However, I (and presumably the AAIB) accept that while this is a reasonable assumption, it would have to be checked out for the subject fuel. I would be amazed therefore if they have not yet measured the specific energy of the fuel. The point remains however, if the SE was low, the aircraft would never have got off the ground. Also, flamibility issues could not account for the apparent cavitation damage.

SOMETHING caused this incident Certainly did, and its clear that the fuel has to be one of the major suspects. However, if it was, I would suspect it was more to do with its fluidity/pumpability in a combined low fuel temperature/lowish fuel quantities (minimising the net positive suction head available) environment than any other quality issues. (Cant recall whether I've mentioned this before, but the viscosity of Jet is specified only at -20C)

tanimbar

5th Jun 2008, 11:50

Some here are saying the -57C freezing point of the remaining fuel is spectacularly low.

Actually this does not seem to be true. If you examine what Shell have to say about fuels around the world, you will read that there are many different grades, different constituent standards and different methods of measuring temperatures.

http://www.shell.com/home/content/aviation-en/productservice/aviationfuels/detail/worldwideciviljet_10081004.html

There are Russian and Chinese sections on the above page. I mention Russia because there have been reports that the indigenous Chinese suppliers cannot produce enough fuel and have been importing Russian equivalents which have "a low freeze point (equivalent to about -57 degrees C by Western test methods)" - quote from the page above.

My view is that we here don't have enough information to make any conclusions about the provenance, name, constitution etc. etc. of the fuel on BA038. All we know is that the AAIB say the fuel, "complied with the Jet A-1 specification".

Regards, Tanimbar

Mariner9

5th Jun 2008, 11:57

Some here are saying the -57C freezing point of the remaining fuel is spectacularly low

They are, but rest assured, it isn't.

If it was TS1, it would not have met ASTM/Defstan Jet A-1 specs for flashpoint.

gas path

5th Jun 2008, 14:08

I'm hoping something might come from a detailed environmental test of the fuel supply chain - no news yet...

The entire fuel manifolding from boost pumps to the engine interface has been removed intact from the left wing and is at Farnborough. It is installed in a test rig for simulation purposes.

Obviously, filtration difficulties would impact on the flow of fuel through aircraft filters, and I would imagine that the effect would worsen with decreasing temperture.
The filters have a bypass! The filter is monitored by the diff. pressure s/w which would send a discrete signal to the engine EEC before the bypass valve opened.
The result would be a status msg. ENG FUEL FILTER L (R)

airfoilmod

5th Jun 2008, 14:11

A friend @ Northrop/Grumman, a Thermal engineer has pointed out the discrepancy that follows. Freezing point of -78, -53, (Average)and -42 Maximum are expressed in degrees Fahrenheit. Quoted OAT (at times) along the noted Flightpath are -78 degrees with Fuel Low Temp of -38 degrees, Centigrade. Should the discussion revolve around values expressed in the same measuring system?

Gas Path, does the Fuel/Oil Heat exchanger also have a bypass, allowing for flow should the Heater Plug Up?

Airfoil

Poof in Boots

5th Jun 2008, 14:40

Gentlemen. Sorry to divert attention away from fuel for a moment

I have trawled through this massive thread and this fact does not appear to have been picked up, with regard to the credit the crew received for their "quick thinking", for reducing the amount of flap at the last moments.

I understand the command for a 'go around' was given, whereby the flap setting would be changed anyway from a landing configuration. If this is so, then the flap retraction and its subsequent benefit, was by default.

Was the command "go around" given?

FullWings

5th Jun 2008, 15:12

I understand the command for a 'go round' was given, whereby the flap setting would be changed anyway from a landing configuration. If this is so, then the flap retraction and its subsequent benefit, was by default.

Was the command "go round" given?
I doubt it, given the situation was a developing undershoot being caused by a lack of power, despite firewalling the thrust levers. What would you "go-around" with at this point?

Not all go-arounds require a change of flap setting, so a call could be "go-around" or "go-around flap X", depending...

airfoilmod

5th Jun 2008, 15:31

Poof, where did that information derive? It's reasonable, and I can't recall seeing it here. With a serious AoA problem and 108 knots @ 200 feet, I think we can say it was an "unstabilized" approach, demanding GA. The 108 knots happened under A/P, so the GA command is definitely something to entertain, whether it happened or not, I think is unknown to most.

Airfoil

Mariner9

5th Jun 2008, 16:13

Correct Airfoilmod, the Grumman report does show temps in F. By conversion, the lowest freeze point they identified was -61C. (Interestingly, the highest freeze point they measured would have been off spec for Jet A-1on that parameter!)

Regarding your point about mixed units, both the prescribed test method for freezing points and Defstan Jet specs both specify the measurements to be in degC.

gas path

5th Jun 2008, 16:26

Gas Path, does the Fuel/Oil Heat exchanger also have a bypass, allowing for flow should the Heater Plug Up?

No! But the FCOC and filter are 'part and parcel' one assembly. The fuel temperature is raised prior to reaching the FCOC as it has already passed through the (LP centrifugal pump) side of the combined engine driven fuel pumps.

apologies for the poor picture!

http://img.photobucket.com/albums/v462/gaspath/untitled-1-1.jpg

airfoilmod

5th Jun 2008, 16:41

Then I see a problem. See Machaca's provided pictures of the Heat exchanger specifically the dozens of narrow tubes in the large cylindrical case. Any transfer of energy requires time, hence the narrow (large surface area) multiple passages. Adding time to passage transit requires restriction. I submit it is a logical place to consider a constriction. Though there are two systems, I refer to an earlier post of mine showing that when independent systems rely on common Fuel (Though stored separately), the possibility is enhanced for failure when certain parameters are shared, and possess an insurmountable extreme, (Temp. Viscosity, restriction, contamination, ambient energy, etc.). This possibility is well within consideration given the seven second delay.

#1159 Machaca, See also Arcniz#1160 for a good interpretation of my
point about heterogeneity in standard and duplicative systems.

Airfoil

seekayess

6th Jun 2008, 20:33

Just read this in an aviation e-mag: wonder if some such thing could have happened in the case under discussion in this forum>>

UPDATE: B-2 CRASH CAUSED BY WATERLOGGED SENSORS

click for video
The crash on takeoff of a 509th Air Wing, Air Force B-2 Spirit bomber, February 23 operating at Andersen Air Force Base, Guam, was caused by water in the aircraft's sensors, according to an Air Combat report issued Thursday. Specifically, moisture in three port transducer units "distorted data introduced by a B-2 Spirit's air data system" which led to flawed information entering the bomber's flight control computers. The aircraft was reacting to inaccurate airspeed and a "perceived" negative angle of attack. This resulted in an "uncommanded 30 degree nose-high pitch-up on takeoff," according to the Air Force.
Major Ryan Link and Captain Justin Grieve, the aircraft's two pilots and the only two aboard were unable to regain control and safely ejected just as the aircraft stalled and mushed into the ground and its left wing impacted the ground. The $1.4 billion aircraft crashed just off the left side of the runway and exploded. It was the first-ever B-2 crash and followed 75,000 hours of loss-free service. Link and Grieve both suffered injuries during ejection, with Grieve suffering compression fractures to his spine.

The report points to the inaccurate readings as contributing factors, adding that ineffective communication of critical information about a technique used to remove moisture from the sensors also contributed. It's possible that all the pilots had to do to avert the accident was turn on the pitot heat prior to performing air data calibrations. But the suggested technique was not part of checklist procedures.

Poof in Boots

6th Jun 2008, 22:13

Well Airfoil.

I think it is quite important to discover whether GA was called. Don't you think to retract the flaps at that moment was 'unusual'? There wasn't an opportunity to discuss the matter with the handling pilot presumably.

Fancy this being overlooked by all you amateur theorists?

bubbers44

6th Jun 2008, 22:20

That is the first thing I would do if struggling to get enough power to reach the runway is attempt a GA.

airfoilmod

7th Jun 2008, 00:24

I think you're confused; a look at the history of the thread would do you well. The Donks conked @ ~800 no power from then on. No one knows whether F/O Coward was attempting GA or simply trying to throttle up while short. The Flaps issue was aggressively dealt with by mods, who diverted all discussion of Flap reselect to JB. Ordinarily one would want a Positive ROC prior to flap retraction, very little is known except the A/P flew up to I think 17 degree AoA and 108 knots at 200 feet AGL. It's not difficult to look like an "amateur" with very little Data, as you now must know. One can Attempt a Go around with no power; One can attempt a HOVER with no power. (Down is Down).

Airfoil

Green-dot

7th Jun 2008, 09:45

If flaps were raised to less than landing position before GA was selected with unresponsive engines (and EAI was not ON), the engine EECs would have automatically reverted from approach idle to minimum idle, aggravating the situation in this particular case. However, there is no mention of raising flaps or GA selection in the AAIB reports.

Green-dot

M.Mouse

7th Jun 2008, 12:13

....the engine EECs would have automatically reverted from approach idle to minimum idle, aggravating the situation in this particular case.

The flaps were reduced from F30 to F25. Approach idle would have been minimum idle speed had the thrust levers been closed, which they weren't anyway.

Even if the flaps had been reduced to less than F25 the idle speed would be irrelevant unless the thrust levers were closed, therefore, I fail to understand how the situation would have been aggravated.

Smilin_Ed

7th Jun 2008, 13:06

Seekayess, I've never flown a B-2, but chances are that pitot heat is ALWAYS on unless selected otherwise. It may well be that they couldn't even select it off except by pulling a circuit breaker and I can't imagine their doing that.

Green-dot

7th Jun 2008, 16:29

To M.Mouse:

The flaps were reduced from F30 to F25. Approach idle would have been minimum idle speed had the thrust levers been closed, which they weren't anyway.

Even if the flaps had been reduced to less than F25 the idle speed would be irrelevant unless the thrust levers were closed, therefore, I fail to understand how the situation would have been aggravated.

There is no mention made about selecting F25 in any AAIB reports i have read sofar. If there was an anticipation to GA, flap selection would have been less than F25, at least to F20, taking the flaps out of the landing position which would mean (as explained earlier) engine EECs would be set for minimum idle. If the thrust levers were even momentarily moved to idle, to minimum idle they would have gone.

Same as for the flap scheduling, there is also no mention if the thrust levers had been retarded to idle, even if only for a short period. Thrust levers in idle, same as your claim flaps were selected to F25, are not mentioned in the AAIB reports but it it does not necessarily mean it did not occur.

Green-dot

bubbers44

7th Jun 2008, 22:57

It seems obvious to me that the flap retraction to 25 was only to clear the fence and maybe make the runway. Nobody in that situation with two sick engines would attempt a go around. No pilot on the face of the earth would have attempted a go around. Why even bring this up? If they had enough power to go around they would have just landed.

M.Mouse

7th Jun 2008, 23:46

Green Dot you are correct here is no mention in the AAIB report of the flaps being moved.

The flaps were retracted from F30 to F25 and the thrust levers were not selected to idle. Your hypothesis is flawed.

Green-dot

8th Jun 2008, 08:57

To M.Mouse:

The flaps were retracted from F30 to F25 and the thrust levers were not selected to idle.

Could you kindly provide a source to back up your statement?

I agree, from a procedural point of view, that it would not be logical to retard the thrust levers to idle in this situation but with unresponsive engines and no thrust increase with the thrust levers fire-walled, would it not be a natural reflex to retard the thrust levers to idle in an attempt to try a last ditch effort to spool up the engines manually, an attempt to initiate a thrust increase from idle conditions?

(Somewhat like gunning your car engine when the engine stalls and you try to recover by letting go of the accelerator and pushing it back in, in an attempt to recover from a stalling engine.)

Regards,
Green-dot

M.Mouse

8th Jun 2008, 09:28

Could you kindly provide a source to back up your statement?

No.

If I know something for a fact I post it to avoid pages of tedious and inaccurate speculation developing.

It really makes no difference to me whether you believe what I post or not. The final report will show whether any statement I have made is right or wrong.

FullWings

8th Jun 2008, 13:09

...would it not be a natural reflex to retard the thrust levers to idle in an attempt to try a last ditch effort to spool up the engines manually, an attempt to initiate a thrust increase from idle conditions?
Not for anyone who was a jet pilot.

About the only time you'd think of retarding a thrust lever when you're undershooting, in an attempt to 'cure' an engine problem, would be if it was surging badly - and this is not the case with BA38.

When people talk about manual thrust on the 777, they mean without the autothrottle engaged. All the A/T does is try to move the thrust levers to satisfy demands from from the A/T computer; when you take it out it means you have to move them yourself. The thrust levers have sensors on them which provide position data to the EECs; that's it. The engines are FADEC = Full Authority Digital Engine Control: there is NO 'manual' control; the only thing you can influence is the mode they operate in - the RR Trent has a 'hard alternate' mode you can select from the flight deck that references N1 instead of EPR and removes some of the thrust (overboost) protection.

It seems obvious to me that the flap retraction to 25 was only to clear the fence and maybe make the runway. Nobody in that situation with two sick engines would attempt a go around. No pilot on the face of the earth would have attempted a go around. Why even bring this up? If they had enough power to go around they would have just landed.
Says it all, really.

CONF iture

8th Jun 2008, 13:34

Not for anyone who was a jet pilot
I disagree.
Green-dot put it right, just a human natural reflex for a mopped driver as well as a jet pilot.
Surprise effect + no time to spare !
That's exactly what did Asseline in Habsheim when he realized thrust was not coming.

FullWings

8th Jun 2008, 13:56

That's exactly what did Asseline in Habsheim when he realized thrust was not coming.
And it helped, did it? :rolleyes:

It's possible to 'rich cut' a carb-fed piston engine by being aggressive on the throttle at a low power setting, on something with an accelerator pump... Maybe people get confused by this and expect jet engines to exhibit the same behaviour.

The only way I know to 'reset' the Trent engine is to momentarily put the fuel control switch into cutoff and hope that it will accelerate up again; even the manual says it could take a loooonnng time. Not a technique I'd apply at 700'. :ooh:

Green-dot

8th Jun 2008, 15:33

To M.Mouse:

The final report will show whether any statement I have made is right or wrong.

Fair enough, patience is a virtue.

To FullWings:

About the only time you'd think of retarding a thrust lever when you're undershooting, in an attempt to 'cure' an engine problem, would be if it was surging badly - and this is not the case with BA38.

Hindsight has 20/20 vision.

In the case of BA038, the crew were confronted with non responsive engines. They had no time to accurately analyse their engine problems. According to the AAIB reports there were no alerts or EICAS procedures to assist the crew. Could very well be that they perceived engine surging to be their problem at hand at the time.

. . .the only thing you can influence is the mode they operate in - the RR Trent has a 'hard alternate' mode you can select from the flight deck that references N1 instead of EPR and removes some of the thrust (overboost) protection.

I am aware of how the system works, including the RR configuration.

In order to select the EEC in the 'hard alternate' mode the pilot has to retard the thrust levers before manually selecting the guarded EEC switch to the 'hard alternate mode' (manual selection is referred to as the 'hard alternate' mode, automatic selection is referred to as the 'soft alternate' mode).

Retarding the thrust levers before selecting the 'hard alternate' mode is necessary because there is no thrust limit protection in the alternate modes (in case of the BA038 situation the thrust levers would have been fire-walled). If the crew had decided to select the 'hard alternate' mode (regardless of an EEC fault or not) they would have retarded the thrust levers before doing so.

To do this, the action is generally triggered by an EEC fault which initially results in a (automatic) 'soft alternate' mode and an EICAS advisory message/procedure. A 'hard alternate' mode selection is the next step in order to acquire a [boxed] N1 reference indication on the affected engine.

Since the AAIB reports explain there is no evidence of EEC faults, hence no alerts such as EEC ALTN light or EICAS messages, logically there would have been no reason for the crew to act and select the 'hard alternate' mode. The only remaining scenario would have been if the crew decided to select the 'hard alternate' mode at their own discretion in an attempt to "wake up" the engines as a last resort. In this scenario they could have retarded the thrust levers to idle although it would not have been necessary to retard the thrust levers that far back.

I stress this probably did not occur or the AAIB would have mentioned it in one of their released bulletins but it could have been a scenario as a last resort attempt to avert premature contact with terra firma in that final minute. If it did occur, it could have resulted in engines reverting to minimum idle if flaps were retracted to less than landing position and EAI not ON. But based on the information that M. Mouse provided (he must have first hand information to back his claim), minimum idle can apparently be illiminated as a factor.

The only way I know to 'reset' the Trent engine is to momentarily put the fuel control switch into cutoff and hope that it will accelerate up again; even the manual says it could take a loooonnng time. Not a technique I'd apply at 700'.

It would have been risky to cycle the spar valves (by selecting fuel control switches from run-to cutoff-to run) which could result in jammed spar valve actuators which would certainly have resulted in fuel flow restrictions.

And it helped, did it?

No but in the BA038 scenario, if this action took place, it didn't either.

Regards,
Green-dot

pool

9th Jun 2008, 03:24

Retarding the thrust levers before selecting the 'hard alternate' mode is necessary because there is no thrust limit protection in the alternate modes (in case of the BA038 situation the thrust levers would have been fire-walled). If the crew had decided to select the 'hard alternate' mode (regardless of an EEC fault or not) they would have retarded the thrust levers before doing so.

If you're out of thrust, retarding is not necessary.
What if they had firewalled with such a switching? - It would have saved their day, wouldn't it?
This is some silly behind the desk comment. If you are in a emergency situation without thrust, you really don't care about technicalities, formalities, bulletins, sops or similar: Anything that gives you a notch more is very welcome....

airfoilmod

9th Jun 2008, 03:51

is saying closed throttles are necessary because Alt mode is locked out at advanced levers, to prevent over speed, No? Once throttles are retarded and Alt mode select is done, then truly manual Fuel control is obtained.(FAMEC?)

Airfoil

snanceki

9th Jun 2008, 06:30

Mariner9 Quote:
SOMETHING caused this incident
Certainly did, and its clear that the fuel has to be one of the major suspects. However, if it was, I would suspect it was more to do with its fluidity/pumpability in a combined low fuel temperature/lowish fuel quantities (minimising the net positive suction head available) environment than any other quality issues. (Cant recall whether I've mentioned this before, but the viscosity of Jet is specified only at -20C)

Mariner9. Thanks for your detailed response.
It is obvious that you know a lot about Jet fuel compliance.

I glean from your response that fuel compliance (or at least production) is as I suspected somewhat of a "Black Art".
Your statement re viscosity measurement only at -20C is interesting.
I still suspect the fuel.

However, I never INTENDED to suggest that the fuel wouldn't burn (although others have suggested this).
I INTENDED to suggest that some property of the fuel caused it to exhibit strange TRANSIENT viscosity characteristics under SUCTION, as in fact you have stated above.
Maybe I didn't express myself clearly enough.

I have NO experience in aviation but as a professional engineer I find it difficult to come to any other conclusion (ON THE INFORMATION AVAILABLE TO US) other than some aspect of the FUEL, conditioned by ENVIRONMENT, and FUEL SYSTEM DESIGN caused a condition that has not been previously considered.

FullWings

9th Jun 2008, 09:05

Airfoilmod,
...Alt mode is locked out at advanced levers, to prevent over speed, No? Once throttles are retarded and Alt mode select is done, then truly manual Fuel control is obtained.(FAMEC?)
There are no 'lockouts' that I'm aware of. Selecting alternate mode makes N1 the controlling parameter and this is referenced to the thrust lever position. This means it is possible to exceed the rated thrust of the engine in certain conditions but not overspeed anything; also, the system is designed so that when you switch, you get at least the thrust you had before, possibly more. If you had firewalled before selecting alt. mode, it's very likely one of the the RPM limits would come into play; at much less than TO/GA to begin with you're unlikely to bust anything.

The manual also says: "If the EECs are in alternate mode, advancing the thrust levers full forward provides some overboost and should be considered only during emergency situations when all other available actions have been taken and terrain contact is imminent." Good one to have up your sleeve if you ever need it...

Green-dot,
Could very well be that they perceived engine surging to be their problem at hand at the time.
I really can't see that: all engine parameters were stable and within limits, just not where they wanted them! An engine surge(ing) is difficult to overlook, even from a mile away... Two very different scenarios, IMHO.

snanceki,
...as a professional engineer I find it difficult to come to any other conclusion (ON THE INFORMATION AVAILABLE TO US) other than some aspect of the FUEL, conditioned by ENVIRONMENT, and FUEL SYSTEM DESIGN caused a condition that has not been previously considered.
I think your comment is pretty much the 'state of the art' at the moment. There are so many possibilities but, like you, I think the probabilities lie here...

PickyPerkins

9th Jun 2008, 14:36

From:
Federal Register / Vol. 73, No. 110 / Friday, June 6, 2008 / Proposed Rules.

DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA–2008–0618; Directorate Identifier 2007–NM–355–AD] RIN 2120–AA64
Airworthiness Directives; Boeing Model 777 Airplanes
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed rulemaking (NPRM).
SUMMARY: We propose to adopt a new airworthiness directive (AD) for all Boeing Model 777 airplanes. This proposed AD would require performing repetitive operational tests of the engine fuel suction feed of the fuel system, and other related testing if necessary. This proposed AD results from a report of inservice occurrences of loss of fuel system suction feed capability, followed by total loss of pressure of the fuel feed system. We are proposing this AD to detect and correct failure of the engine fuel suction feed of the fuel system, which could result in dual engine flameout, inability to restart the engines, and consequent forced landing of the airplane.
DATES: We must receive comments on this proposed AD by July 21, 2008.
---- END QUOTE -----
No mention of using any specific grade or type of fuel, or of testing at low temperatures, just testing.

P.S. Many thanks to precept for the link to the US Government AD Notice Search Location in his/her Post #1135 on 13th May, 2008. http://pickyperkins.home.infionline.net/pi.gif

soem dood

9th Jun 2008, 15:40

Thanks!

The docket contains more detailed info, such as:

Discussion

We have received a report of in-service occurrences of loss of fuel
system suction feed capability, followed by total loss of pressure of
the fuel feed system. This condition, if not corrected, could result in
dual engine flameout, inability to restart the engines, and consequent
forced landing of the airplane.

FAA's Conclusions

We have determined that it is necessary to require an operational
test of the engine fuel suction feed of the fuel system, and other
related testing, as applicable. Procedures for doing the operational
test can be found in the maintenance manual. The other related testing
is for airplanes on which one or both of the engines stop idling in
less than five minutes after starting the test. Failure of the engine
fuel suction feed of the fuel system could result in the unsafe
condition described previously.
...
Applicability

(c) This AD applies to all Boeing Model 777-200, -200LR, -300,
and -300ER series airplanes, certificated in any category.

Unsafe Condition

(d) This AD results from a report of in-service occurrences of
loss of fuel system suction feed capability, followed by total loss
of pressure of the fuel feed system. We are issuing this AD to
detect and correct failure of the engine fuel suction feed of the
fuel system, which could result in dual engine flameout, inability
to restart the engines, and consequent forced landing of the
airplane.

...
Operational Test/Other Related Testing

(f) Within 7,500 flight hours after the effective date of this
AD, perform an operational test of the engine fuel suction feed of
the fuel system, and perform all other related testing, as
applicable, before further flight, according to a method approved by
the Manager, Seattle Aircraft Certification Office (ACO), FAA. One
approved method is the operational test in Section 28-22-00, titled
``Engine Fuel Feed--General Description,'' of the Boeing 777
Aircraft Maintenance Manual; and Boeing 777 Task Card 28-020-02-01,
titled ``Fuel Feed Manifold,'' dated May 5, 2007. Repeat the
operational test thereafter at intervals not to exceed 7,500 flight
hours.http://edocket.access.gpo.gov/2008/E8-12691.htm

airfoilmod

9th Jun 2008, 15:43

If True, and the cause of BAE038 mishap, Renton/Rolls have some 'splainin to do. IMHO

bsieker

9th Jun 2008, 15:56

Thanks for the pointer to the docket, it's an interesting read.

However, I don't see its relevance to BA 038.

According to the AAIB's reports ...

[...] the aircraft fuel boost
pumps were serviceable and operated correctly during
the flight.

So, no suction feed.

If some sort of condition was present on flight BA038 that restricted fuel flow even with the boost pumps operating, why would the FAA propose rulemaking specifically for the case of suction feed?

Bernd

Torquelink

9th Jun 2008, 16:01

Similar NPRM issued for 747-400 too.

777fly

9th Jun 2008, 16:18

You might like to refer to my posts, some pages ago, concerning the possibility of trapped air in the fuel suction feed disrupting the fuel supply when released.

Page 28 post 555 para 4. If I knew how to cut and paste, it would be here:

airfoilmod

9th Jun 2008, 16:27

Just because Boost pumps are operating, does this mean suction feed was not compromised in other ways? The 777 was designed to operate sucking Fuel only, w/o pumps. The cavitation on the High side of the HP engine pumps points strongly to a lack of available Fuel, which means that demand was overpowering supply. To me, this means that the pumps/filters/flow somehow caused the problem, in other words, if the aircraft can run just fine (By Test) at all settings on suction alone, what in addition to suction only would cause the FAA to distribute a Rule that referenced "Dual Flameouts"? AoA? Fuel Viscosity? Fuel Temperature? Sensing Failures? #1 I feel this incident is not complicated, #2 AAIB/FAA have had the solution for some time, #3 Proper time is passing for reasons other than the complexity of the challenge.

Airfoil

CONF iture

9th Jun 2008, 17:42

One approved method is the operational test in Section 28-22-00, titled ``Engine Fuel Feed--General Description,'' of the Boeing 777 Aircraft Maintenance Manual; and Boeing 777 Task Card 28-020-02-01, titled ``Fuel Feed Manifold,'' dated May 5, 2007
Any detail on that test ... ?

gas path

9th Jun 2008, 18:26

There currently is a pressure test carried out at I believe 'A' check level.
So the penny has finally dropped to include the 744.... I wonder why that is;);):D
The 744 AMM will require a rewrite to include a vacuum check.:hmm:

Green-dot

9th Jun 2008, 18:59

To Pool:

If you're out of thrust, retarding is not necessary.
What if they had firewalled with such a switching? - It would have saved their day, wouldn't it?
This is some silly behind the desk comment. If you are in a emergency situation without thrust, you really don't care about technicalities, formalities, bulletins, sops or similar: Anything that gives you a notch more is very welcome....

Although i agree with you this was an emergency situation and lacked thrust, i was only explaining how the system functions, how the 'hard alternate' mode is designed and operated. Obviously it was not designed with the BA038 incident in mind. Fact remains that there is no thrust limit protection and that is why thrust levers are (partially) retarded if fire-walled and that is how operation in this mode is trained. N1, N2, and N3 overspeed protection remain available. Again, with hindsight, in the case of BA038 none of these limits would probably have been reached. And again with the crew not exactly knowing what was affecting the engines might or might not have followed trained alternate mode procedures, all hypothetical anyway because they had no indication or alert to select the alternate mode and most likely never did.

airfoilmod:

Alternate mode selection does not lock out the thrust levers which, in this case, do not have to be fully retarded to idle and as FullWings explains, in this mode N1 becomes the controlling parameter.

Green-dot

lomapaseo

9th Jun 2008, 19:26

Some random thoughts on this AD

It seems to be a data gathering and not a conclusion.

7500 hours does not relate to a confirmed safety of flight situation.

But it is movement in a direction to at least gather pro or con information about a possible problem in a timely manner.

It reminds me of the initial response to the fuse pin issue with the B747 between CI and El Al accidents.

So I will await the inspection results (data vs postulations)

precept

9th Jun 2008, 21:03

A direct link to the FAA document regarding 777 suction feed follows. Interested parties may want to click on the imbedded links to both the Docket and to the Document. Comments by the Airlines and interested parties are posted on the Docket response. As can be seen Air New Zealand has already posted comments.

http://www.regulations.gov/fdmspublic/component/main?main=DocketDetail&d=FAA-2008-0618

Oldlae

9th Jun 2008, 21:08

My knowledge of the 777 fuel system comes from this thread, however, a suction test indicates that the engines are run and the boost pumps switched off, if the engines run down, it would appear that air is entering the system. Air could enter the system from, for instance, a NRV not seating properly. That both engines on BA038 ran down at the same time is still peculiar. This AD addresses the system not the fuel.

FullWings

9th Jun 2008, 21:57

It still doesn't make sense, though. With the tank pumps running and the manifold(s) pressurised, fuel is going to leak out rather than air leak in... Unless there was a massive failure of NRVs leading to a kind of short circuit in the fuel supply... But even then, the fuel in the pipes is still at a higher pressure (atmospheric plus a bit of gravity feed) than that at the entry to the engine pumps. :confused: Still pointing towards some sort of restriction, I feel.

Oldlae

9th Jun 2008, 22:36

If a NRV or PRV is in the system to bleed off excess pressure when the boost pumps are operating, it would not be an external leak when it is working correctly as it is doing the job it is designed for, depending on the pressure it is set at. But if the valve is not seating as it should air can be drawn in from the return line.

Swedish Steve

10th Jun 2008, 07:19

Any detail on that test ... ?

Wing boost pumps ON. Start engines and run at idle-
Turn off APU (to disable APU boost pump)
Switch off all 4 boost pumps.
Engine shall run at idle for 5 minutes.
If not look for leaks in suction feed system.

When I used to do this on the L1011, we did it at take off power. Turned off all the boost pumps at take off and watched that nothing else happened. The engine always continued to run as normal.

arcniz

10th Jun 2008, 07:57

The 7500 hours from publication allowance in the testing requirement suggests a complete lack of any sense of urgency in this inquiry. Cold prospect as far as they're concerned.

racasan

10th Jun 2008, 08:17

The NPRM's have been issued to all Boeings apart from the 717 as far as I can see

Terraplaneblues

10th Jun 2008, 08:20

A similar test was called up on the 737-200, much as described by Swedish Steve, but the fuel level had to be quite low, actual figure escapes me, so as to uncover the most of the in tank fuel tubing. The method will work on any aircraft and has been used with success to find holes & bad joints on the in tank fuel tubes.

FlyGooseFly!

10th Jun 2008, 18:45

Forgive me for not checking all sixty odd pages of this thread for the answers to the following.

Is there a temperature sensor anywhere near the fuel pumps - particularly the H.P. ?

Is that data recorded anywhere ?

What was the temperature of the fuel either side of the H.P. pumps at the time of engine failure ?

airfoilmod

10th Jun 2008, 20:58

There is one Fuel Probe (Temp. Sensor) Data stored in FDR. It is located between Ribs nine and ten in the Port Wing, about one meter aft of the Boost Pump Pickup as I recall.

Airfoil

(Lowest Recorded Temp. Fuel was -38C.) And the Port wing was on the Sun Side of the A/C for that flight.

777fly

11th Jun 2008, 17:23

It is interesting that the FAA are now looking at the suction feed.Here is my post from way back, which may be an explanation:

There is actually one instance in which Boeing suggest that a fuel supply problem can cause engine thrust deterioration or flame out. This is when an engine has to revert to suction feed at altitude, following dual wing tank pump failure. (No mention is made of the low altitude situation.) The background to this advisory is that dissolved air in the fuel is released at altitude and can accumulate in the suction feed pipe. The implication being that low atmospheric pressure in the tank, plus air in the suction line will disrupt or cut off the fuel flow under suction conditions.

Note from the fuel synoptic posted by Jet11 that the suction pipe is connected directly to the engine fuel supply manifold, isolated only by a pressure bypass valve. Also that the tank pump nominal output pressure is 14psi, but can be much lower. For argument's sake, I will assume that the suction bypass valve opens when there is a pressure differential around 5 psi and it closed under normal conditions.

In Bejjing, BA038 takes on fuel with an unusually high dissolved air content. This is due to a combination of production/storage/transportation/pumping and weather variables. The a/c flies high, long and cold. The air is released from the fuel and the suction pipe is completely filled with (relatively) dense air. This air remains in the pipe during the descent and once below 6000ft is inceasingly pressurised by denser ambient air and rising temperatures. At 1000ft atmospheric pressure reaches 14psi, equalling the fuel manifold pressure. Fuel hydrostatic static pressure and adiabetic heating add another 6psi, causing the suction bypass valve to open against tank pump pressure.This releases pressurised air into the fuel supply manifold and disrupts the fuel supply. This happens in both tanks, but not simultaneously. The opening of the valve could be assisted by a momentary drop in fuel manifold pressure during the initial power demand.

Just another theory. My assumptions about the bypass valve are probably wrong. Also, why is this not a regular occurence? Maybe the fuel and meteorological conditions were unique to BA38. Maybe we have always been operating close to this scenario.........

Mr @ Spotty M

11th Jun 2008, 21:36

Don't put to much on this AD, as this has been known about for over two years or more.
You will find that this task has been in operation for a few years and BA may have been doing it on its B777 fleet.
I was at a Boeing engineering committee a few years back on the B757 series and we were told that a new task was being introduced to carry out a fuel suction test, which we voted to accept.
I remember way back this being done on the old B737-200s and we were told at our meeting it had come about from findings on the B777 fleet. Due to the fuel system on the B757 being similar to that of the B777, it needed to be brought in. We discussed the interval that was proposed and made amendments to the interval and was as l said accepted.
We were told if we accepted the task, it would mean that it should not have to be made an AD. This task was introduced into our "C" checks two winters back.
So if the same thing has happened to the B777, l would guess it has been carried out for a couple of years.
The main reason for the task, is when you get low fuel quantity you may suck air in, if the fuel pipe seals are leaking. You need a very low fuel figure in each tank to carry out the check using engine runs or you have go into the tanks and use test equipment instead to check the piping.

airfoilmod

11th Jun 2008, 21:43

But are you assuming the T7 has a separate supply, isolated from the pumps/line that "takes over" when Pumps inop? The mass of Fuel in the pipeline has great inertia at low/no velocity and with HP functional at 14psi (or slightly greater) could vaporise regardless of Temp. One atmosphere is ~ 14psi, right? In a "tail low" approach, the suction problem could be exacerbated by the inertia of the Fuel and its lethargic velocity in the Line due to Green descent. Haven't we been there? (Besides, the pumps were working, AAIB)

Airfoil

F111D

12th Jun 2008, 05:05

I am suprised no one has picked up on this.

http://www.ainonline.com/news/single-news-page/article/fuel-system-remains-focus-of-investigation-into-ba-777-crash/ (http://www.ainonline.com/news/single-news-page/article/fuel-system-remains-focus-of-investigation-into-ba-777-crash/)

Fuel system remains focus of investigation into BA 777 crash

By Ian Goold
June 1, 2008
Accidents

Safety officials probing the circumstances leading to the January 17 accident of a British Airways (BA) Boeing 777 at London Heathrow are continuing to focus on the fuel system. In particular, they want to know why the aircraft lost power when it was on final approach.

The 777, operating as flight BA038, was flying nonstop from Beijing to London Heathrow. The flight was uneventful and the engine operation was normal until the final approach. As the 777 approached to land, the R-R Trent 895 engines initially responded to an autothrottle command for increased thrust. At a height of about 720 feet, thrust on the right engine reduced to about 1.03 times the engine pressure ratio (EPR), followed about seven seconds later by a similar reduction (1.02 EPR) on the left engine.

The airplane touched down 1,000 feet short of Runway 27L’s paved surface before coming to rest in the undershoot area astride a taxiway junction near the threshold. In the heavy landing, the nosegear collapsed and the left main undercarriage was punched up through the upper surface of the wing, while the right undercarriage six-wheel bogie detached from the aircraft. One passenger was seriously injured and 12 other occupants received minor injuries. The airplane sustained heavy damage and was subsequently written off.

The UK Air Accidents Investigation Branch (AAIB) has determined that in the case of both engines, thrust reduction resulted from reduced fuel flow, which was reflected in all subsequent engine parameters. Although the fuel-metering valve responded to an engine-control system command to open fully, there was “no appreciable change” in fuel flow. Evidence indicated that both engines had “low fuel pressure at the inlet to the high-pressure pump.”

Following “sustained interest” in the accident, the first such event involving a 777, the AAIB last month published a special bulletin that said Boeing Commercial Airplanes division was conducting fuel-system testing in Seattle. Engine manufacturer Rolls-Royce had earlier completed “extensive full-scale engine testing” in a cell modified to replicate the actual response of the accident aircraft’s engine fuel and control system.

AAIB investigators say the primary challenge was for Boeing to create the environmental conditions the flight experienced while flying over Siberia at altitudes of up to 40,000 feet. The flight over the region took the 777 through particularly cold air, as low as -76 degrees Celsius (-104.8 degrees F). The minimum recorded fuel temperature was -34 degrees Celsius (-29.2 degrees F) and subsequent tests of onboard fuel showed a freezing temperature of -57 degrees Celsius (-70.6 degrees F).

Investigators are principally concerned with understanding the potential for
fuel-system restrictions to have formed. Additional work has aimed to improve understanding of fuel-flow dynamics between the tank and the engine.

Systems consultancy Qinetiq is reviewing recorded data from a large number of similar flights. Qinetiq analysts are concentrating on the identification of abnormal combinations of parameters, since no single reading from the accident flight has been identified as outside previous type operating experience.

HotDog

12th Jun 2008, 05:14

I guess you couldn't be bothered to read through the 68 pages of this thread?:bored:

cwatters

12th Jun 2008, 06:33

F111D - A summary of 68 pages... The evidence for lack of fuel flow appears to be limited to minor cavitation damage to the pumps (Minor in the sense that it did not stop them working). The issue is what caused the low fuel pressure/flow in the first place. It appears there was sufficient fuel on the plane.

777fly

12th Jun 2008, 07:57

Airfoilmode:

No, I am not suggesting that the suction system has its own fuel supply line. There is a short section of pipe that joins the main fuel supply manifold, via a check valve, just downstream of the LP tank pumps. I would not see fuel inertia as a problem there.

What I suggested was that air or gas that was trapped in the suction pick-up pipe might, under certain circumstances, become sufficiently pressurised to enable it to overcome the check valve differential and discharge like an aerosol into the main manifold. When this air/gas reached the engine HP pumps it would cause cavitation as the pumps ingested air and fuel supply to the engines would be reduced, similar to the situation where a diesel engine loses pressure at the injectors if air gets in the system. No doubt the LP pumps would have restored manifold pressure eventually, but in BA038's case there was insufficient time before the accident occurred.

Maybe the check valves have prevented this situation up to now and BA038 was the first unlucky one. Running a suction check from time to time would certainly remove any trapped gases in the system.

Rightbase

12th Jun 2008, 21:40

777fly-

Air bubbles in the fuel do not cause cavitation damage. The air cushions the collapse of the air bubble, so the bubble does not disappear when pressure is restored, and there is no damaging shock wave.

Oldlae

13th Jun 2008, 12:22

Bulletin S3 out in AAIB June report.

BOAC

13th Jun 2008, 13:43

To save you rushing to download, there is nothing of note in it, and still no mention of a config change, and no rec. of any changes in operating procedures.

Globaliser

13th Jun 2008, 15:38

Indeed - in fact, it looks to me like it's exactly the same document as was published on 12 May 2008, just formatted differently to be incorporated into the Bulletin.

Flight Safety

13th Jun 2008, 15:56

Rightbase is correct, air in the fuel stream will not cause cavitation damage, for the reasons he stated. This was caused by a fuel obstruction or restriction.

In fact, if you think about it, cavitation damage from suction would seem to confirm integrity of the fuel manifold.

cwatters

14th Jun 2008, 09:58

When the freezing point of fuel is measured on the ground is the resulting figure corrected for the increased pressure found in the fuel system?

I think the freezing point of fuel (but not water) is raised by increasing pressure. In which case you might speculate on the possibility of having liquid fuel in the tank... which then freezes in the pipes/pumps when pressurised.

This effect probably isn't great enough though.... -34C to -57C is a bit of a stretch and the architecture of the 777 fuel system may also rule this out.

Edit: Initially when you compress something heat is given out which raises the temperature. At high flow rates the fuel might remain warmed. At low flow rates perhaps this heat has time to disipate leaving the higher freezing point to cause the problem. If that's correct it might explain why this didn't happen in cruise just on approach.

Green-dot

14th Jun 2008, 12:21

Or it might just be the difference between finding the fault on a complete and serviceable airplane and not finding or unable to duplicate the fault on an incomplete and twisted one?

For instance, if something was in error in the last few minutes of the flight, a sequence of system selections unique to the approach phase only, which generated a rogue electrical spike that did not make it to the recorders somehow? Maybe the temperature in the fuel tanks had nothing to do with the cause at all, perhaps humidity, pressure and temperature inside the hull and miles of wiring and electronic units did?

Green-dot

PickyPerkins

14th Jun 2008, 14:57

Don't put to much on this AD, as this has been known about for over two years or more.
I think you will find that the airline industry has known about problems of transitioning to suction feed on Boeing airliners since at least 2001, a lot longer than two years ago:
http://www.pprune.org/forums/showpost.php?p=4000971&postcount=1101 (http://www.pprune.org/forums/showpost.php?p=4000971&postcount=1101)

FAA has specifically said the suction AD is nothing to do with BA038.
I missed this.
Can you provide a link to this statement by the FAA that the AD has nothing to do with BA038?
Thanks. http://home.infionline.net/~pickyperkins/pi.gif

airfoilmod

14th Jun 2008, 15:16

As has been addressed before, the Trent/777 does just fine in Suction only regime. Also, prior post (recent) explains that a non uniform Fuel supply (eg entrained air) would prevent cavitation, not cause it. Air/Water/Additives in the Fuel have been addressed pretty much ad nauseum. I think the chances the AD is related to BA038 are quite slim, except as it may apply to the Fleet in general, though not nil. (Consider 7,500 TBI per AD)

My sense of the cavitation problem would require cold Fuel in a tight system, devoid of easily vaporised contaminants, subjected to a sudden throttle slam shock with HP's straining at a volume of Line Fuel that has substantial inertia, creating cavitation, which in turn would inhibit the free flow of Fuel. A perceived restriction/block is in there as well.

Airfoil

Oldlae

14th Jun 2008, 17:25

cwatters, hi again,
A minor point, fuel cannot be compressed just pressurised although any air present would be compressed.

Mr @ Spotty M

14th Jun 2008, 20:33

"PickyPerkins", your link has nothing l believe, to do with this AD.
As l pointed out this MRB task and now being made into an AD, is all about air being sucked into the fuel tank piping from within the tank, from worn seals where the pipes join each other.
This happens with very low fuel state and would not happen just after take-off.
What happened to the UA aircraft, is l believe not related to this extra task introduced from the MRB and now mandated.

India Four Two

15th Jun 2008, 03:54

Oldlae,

All liquids are compressible to some extent, even water.

There are some values for Jet A1 quoted here:

http://www.eng-tips.com/viewthread.cfm?qid=155581&page=1

I have no idea whether this is material to the BA038 accident, although with the low pressures involved, I suspect not.

barit1

15th Jun 2008, 13:34

Both the plumbing and the fluid therein (fuel, possibly with air or vapor) have elastic properties: they store energy when under stress, and give that energy back when the stress is removed. That's all it takes to have the potential for resonance, which was discussed a few pages back. I trust this is being studied until some better candidate emerges.

lomapaseo

15th Jun 2008, 14:32

Both the plumbing and the fluid therein (fuel, possibly with air or vapor) have elastic properties: they store energy when under stress, and give that energy back when the stress is removed. That's all it takes to have the potential for resonance,...

Agree

which was discussed a few pages back. I trust this is being studied until some better candidate emerges.

But what is the forcing function and the response :confused:

barit1

15th Jun 2008, 15:35

But what is the forcing function and the response

THAT, of course, is the $64 question (am I showing my age?)

One excitation possibility is the gear tooth passing frequency (assuming a gear-type HP pump).

Flight Safety

15th Jun 2008, 16:02

Since both engines initially responded to the autothrottle with increased thrust, that meant the restriction or obstruction was not in effect yet, at least not initally. Then within 3 secs or so, the right engine rolled back to EPR 1.03, with the restriction or obstruct in effect, with low fuel pressure present and HP pump cavitation damage taking place. The same sequence occurred for the left engine, although the rollback in power to EPR 1.02 occurred 7 seconds later. In other words the restriction or obstruction developed slightly later for this engine.

This suggests to me that the sudden increase in fuel flow required for the power increase, is what actually triggered the formation of the restriction or obstruction (whatever it was), which apparently was not present in the first few seconds of increased fuel flow.

I'm not sure what that means, but this appears to be the sequence of events. High fuel flow was available initially, then the restriction or obstruction developed (perhaps precipitated by the sudden increase in fuel flow), then low fuel pressure and HP pump cavitation followed and remained in effect until impact with the ground.

Of course the million dollar question is, what was the nature of the restriction or obstruction, and how could a sudden increase in fuel flow rates possibly cause it?

ChristiaanJ

15th Jun 2008, 16:34

Flight Safety,
Without any more AAIB input we're back to guessing games....
But your post makes for an interesting question.

What was the fuel flow in m/sec or ft/sec ?
In other words, if it was indeed some kind of obstruction, how far did the 'slush puppie / chinese noodles / wad of chewing gum' travel after being dislodged, to arrive after 3 secs on one side and 7 secs on the other side?
Maybe there's a clue there?

CJ

airfoilmod

15th Jun 2008, 16:35

Daniel Bernoulli, whose work with Hydraulics may have a hint to help the discussion. His most widely known discovery was that a fluid (inviscid Fluid, not "compressible") that was accelerated in a tube, created a concomitant reduction in pressure within. The Fuel line in 038 was subject to sudden demand. Cavitation at the HP (both) has been described and bears further thought. As an "incompressible" mass, the Fuel in the Line would transmit the focal cavitative results on the High side of the Pumps back through the system. In essence, the massive pressure at the Pump Lobes would communicate back through the Fuel and have an instantaneous effect on other mobile mecnanical devices in Line. Air "cavities" would have developed and perhaps failed backflow valves, Spar valves, and LP (boost) pumps back through the system. The Fuel in the Line is a "Hammer" that takes the shape of the System, but retains its abilities to hamper normal supply throughout the entire Fuel System.

Airfoil

(Suggesting there may have been no "obstruction", other than the Fuel itself, having created an insufficient flow due to inertial reluctance which may have failed other intersections)

ChristiaanJ

15th Jun 2008, 17:13

airfoilmod,
Phenomenon also known as "water hammer" to your local plumber.
Known to every fuel and hydraulic system engineer.
As an explanation for what happened on BA038 it seems somewhat far-fetched.
Not to mention, that any "fuel hammer" effect is nearly instantaneous. It does not take 3/7 seconds to manifest itself.

airfoilmod

15th Jun 2008, 17:24

And the theory has more to do with resonance and harmonics having an effect on mechanicals than a "Hammer". I used the term to convey the communicative effect of pressure differentials in an "instantaneous" way.

"Hammer" is an effective way to understand cavitation, notwithstanding your derisive retort to its use. I didn't think it would bother anyone, I'll be more careful with my vocabulary.

RGDS Airfoil

(BTW, if you've noticed Water Ram, you will also have noticed its brother, Recoil. That vibration, and "return,rebound" of the Ram, stops flow.)

cwatters

15th Jun 2008, 17:54

Anyone got a phase diagram for jet fuel?

airfoilmod

15th Jun 2008, 18:07

Rather coy way of introducing doubt and suspicion of the Flight Crew, No?
Coupled with your statement on another thread, why don't you just man up and state your point.

cwatters: Awesome, now you're talking.

Airfoil

arcniz

15th Jun 2008, 18:35

Anyone got a phase diagram for jet fuel?

That may be hard to come by. Problem is that typical fuels are not an "it", but a complex and widely varying collection of complex components blended to meet a set of specs. A batch could consist primarily of ground-up gerbils and would likely not be rejected if it met all the specs.

Similar might be said for various of the aircraft systems involved -- they are designed to meet reasonable specs derived from science, engineering, and experience. Sometimes circumstances arise that have not been fully contemplated in the specs, and unanticipated results ensue. BA038 may well be one of those situations where tried-and-true standards and specifications did not prevent a unique special case from having adverse effect.

PickyPerkins

15th Jun 2008, 20:26

As has been addressed before, the Trent/777 does just fine in Suction only regime.
So did the UA 767 referred to in my link:
http://www.pprune.org/forums/showpost.php?p=4000971&postcount=1101 (http://www.pprune.org/forums/showpost.php?p=4000971&postcount=1101)

The engines on the 767 performed just fine in suction all the way from sea level to 41,000 ft.

What they could NOT handle was a cessation of boost pressure during the climb.
The engines spooled down 14 seconds after the boost pumps were turned off.

Exposed leaky pipes and seals were not involved because the tanks were full.

This seems a clear indication to me that the boost pumps were doing something which the HP pump could deal with so long as boost pressure continued.
But when boost pressure was discontinued, the engines spooled down after a delay of 14 seconds.

That something which boost pumps were doing could have been bringing air out of solution.
Which was OK with boost pressure on, but not OK when the boost ceased.

Air bubbles in the fuel do not cause cavitation damage. The air cushions the collapse of the air bubble, so the bubble does not disappear when pressure is restored, and there is no damaging shock wave.
Also, prior post (recent) explains that a non uniform Fuel supply (eg entrained air) would prevent cavitation, not cause it.
In the case of BA038, does it really matter whether air bubbles did or did not cause cavitation damage?

The AAIB says although there was cavitation damage, it was not sufficient to prevent the fuel being pumped. The damage was not significant wrt pumping capacity.

What matters is - why did the fuel stop advancing through the system?

More than 30 years ago a Royal Aircraft Establishment repot by WGS Lester, “Temperature and Fluid Effects on Cavitation in Aircraft Fuel Pumps” showed that air coming out of solution could cause the volume output of centrifugal type boost pumps to fall markedly.

He was not concerned about cavitation damage, only about whether the pump continued to deliver fuel.

With air dissolved in the fuel, his test pump didn’t stop pumping, but the output volume fell.
Sound familiar?

And the fall off in performance was greater when the fluid was cold.
Sound familiar?

In fact the pump output was greater when the test liquid was boiling (no dissolved air) than when it was cold (with dissolved air).

Some of his test results are shown in:
http://www.pprune.org/forums/showpost.php?p=4004624&postcount=1102

Fuel saturated at room temperature becomes highly supersaturated when cooled.
It typically remains supersaturated for many hours in aircraft fuel tanks at altitude.
This was mentioned by Lester, and confirmed decades later in Boeing test flights.

Bottom line
The difficulty in finding the restriction to fuel flow maybe because there was no restriction to flow, just a fall-off in boost pumping capacity due to air coming out of solution from cold fuel, and a mixture of air bubbles and fuel delivered to the HP pump.
Just my 2cents. Maybe 1 cent. http://home.infionline.net/~pickyperkins/pi.gif

airfoilmod

15th Jun 2008, 20:44

You may be intermingling two separate causes of Fuel restriction or Flow reduction. Your reference to dissolved air or air (Gas) in the Lines reducing pump efficiency sounds a whole lot like "vapor Lock" (or Block). It is a serious problem in pressurised Fuel systems, but one wonders of its relevance here. Also, a "foaming" supply of Fuel would mimic starvation, even if Flow continued. Cavitation, having been demonstrated, has stolen all the attention, and is an unrelated (presumably) failure, unconnected to dissolved gases in Fuel (to my understanding).

Airfoil

Joetom

15th Jun 2008, 22:13

Just a point if interest.

Fuel flow could have been restricted for a long period of time.

Think of Spar or LP valve being in a position between open and closed, Engine will run Ok upto a point, but when FMV/FMU needs more flow than avail, problems will start, problems may be delayed a little with the head of fuel down stream of restriction, but problems on the way.

barit1

15th Jun 2008, 23:57

What might the 777 cruise fuel flow have been just before TOD? (call this point A)

And what fuel flow might have been demanded on a normal close final? (call this point B)

Between these two points, fuel flow was at a very low level. Is it possible the restriction existed (without symptoms) at A, and didn't become evident until thrust advance at B? :confused:

airfoilmod

16th Jun 2008, 03:55

Or Point B plus 3 and then plus seven seconds, the time needed to make the restriction critical ? Think you're on to it.

snanceki

16th Jun 2008, 08:00

It never ceases to amaze me how "creative" individuals can be.
After all, this is the purpose behind brainstorming!

Only problem is that each "theory" has to be "understood" and either moved forward to the "possible" file or discarded due to some misunderstanding/lack of knowledge by the proposer.

I was particularly "impressed" by your "definitive" conclusion that there was adequate fuel on board after resolving the frost pattern on the underwing from a photo a few seconds before the crash landing.

Now the various "theories" put forward in the last few pages of posts, many seem to focussed around the cause of the "restriction" without any data in support of the nature of any such restriction.

In order to try to get you guys to be creative in a slightly different direction I wonder what are your thoughts are on the "size" of the restriction?

By this I invite your energy into determining the following:
1. What fuel consumption (flight idle?) would exist on approach prior to the incident. Ltrs/sec or whatever.
I don't have any idea what these big fan jets consume even at idle but its certainly "significant"!
2. What capacity (volume) exists in the fuel lines between pickup and engine spray nozzles?
Is this the same on both sides of the aircraft or slightly different and if so which side has the greater volume and why?
3. Is it possible to resolve this volume more accurately. i.e. what %age of the previous volume exists between pickup and lets say the spar valve, heat exchanger or HP pump.
4. How long would it take to use this volume with 100% "block" at whatever thrust setting was likely to have been called for during final to offset flap etc (which wasn't delivered when requested).
I appreciate that full thrust was at some point selected but it was a much lower power request that highlighted the problem..
DO THESE FIGURES MAKE ANY SENSE?
So we could deduce 75%, 50% etc restriction vs duration.
Unless these figures make sense, discussing the possibility of Bernoulli type restriction etc seems a little premature (although possible) especially since such an occurrence has not been experienced during multi million previous landings. So what was different this time around?

As a professional engineer, but unfamiliar with the "detail" of aircraft installations, the 7/8 secs is in my view highly relevant.
The difference between 7 and 8 secs on the other side may NOT be relevant but explained by deficiencies in the measurement (DFDR sampling rate) process or subtle differences in the level of thrust commanded. However it MAY be significant if indeed the capacity of the system is indeed different LH to RH.
However a "significant" amount of fuel would be used during a 7 secs period. So how about a few FACTS even if these are derived from from first principles.
The AAIB have access to the real data so I guess they will have already been through an exercise something like this.

Maybe you will just overlook my request / maybe not!

Finally, am I correct in my understanding that BOTH LH and RH boost pumps WERE WORKING and that this was actually confirmed by the AAIB...I'm too lazy to go and reconfirm! If so why the discussion about what would happen if the pumps weren't running and the possibility of air being drawn in with low tanks etc.

CONF iture

16th Jun 2008, 13:15

As a professional engineer, but unfamiliar with the "detail" of aircraft installations, the 7/8 secs is in my view highly relevant
At first sight the 7 or 8 seconds difference could have been explained by a single fuel source going through a fuel crossfeed valve ...
I believe that kind of engine must be around 1000kg/H at ground idle, so flight idle would not be far from 1 Liter every 2 seconds

ChristiaanJ

16th Jun 2008, 13:28

Thanks!
Half a litre per second is as good a ballpark figure as any.
Now what's the diameter of the fuel feed pipe?

snanceki

16th Jun 2008, 14:49

At first sight the 7 or 8 seconds difference could have been explained by a single fuel source going through a fuel crossfeed valve ...

Need to correct you. The DIFFERENCE between LH and RH installation was only 1 sec.
Roll back occurred after 7 or 8 secs.
Sorry if 7/89 looked like a fraction.

infrequentflyer789

16th Jun 2008, 17:23

Need to correct you. The DIFFERENCE between LH and RH installation was only 1 sec.
Roll back occurred after 7 or 8 secs.
Sorry if 7/89 looked like a fraction.

Hate to correct a correction, but according to the AAIB the difference was around 7 seconds, not only 1 sec:However, at a height
of about 720 ft the thrust of the right engine reduced to approximately 1.03 EPR (engine pressure ratio); some seven seconds later the thrust on the left engine reduced
in addition to any asymmetry in the fuel feed geometry (possibility mentioned recently), there are other asymmetries which might possibly be relevant when looking at this difference.

eg. Fuel levels were not identical in each wing (300kg difference I recall), and also one wing would have been in sun and the other in shade, therefore likely to be some temparature difference.

airfoilmod

16th Jun 2008, 17:44

That another poster has noticed the sunny side was to Port.

Airfoil

(especially in conjunction with #1, #2 "jet lag" as it were)

johngreen

16th Jun 2008, 19:29

ChristiaanJ
As the troublemaker who suggested resonance a few pages back I would have to agree with you that ‘As an explanation ...it seems somewhat far fetched’. However it seems whatever is finally determined as the cause of this fascinating problem is going to be something quite out of the ordinary given that this is still apparently eluding every attempt at exposure by the amassed genius of the AAIB, Boeing and PPrune correspondents to mention but a few!

Your further statement ‘…any “fuel hammer” effect is nearly instantaneous…’ is however absolutely untrue and very misleading.

Lomapaseo

In order for resonance to occur within the fuel system, I suggest that there is not one simple explanation that will satisfy the enquiry ‘But what is the forcing function and the response’ beyond the observation that there are pumps providing energy to a flexible structure (pipework and fuel) that includes non return valves which in certain very unusual and very undesired circumstances have the potential to block the flow of fuel as well as to more normally allow it to pass.
It is the (very unusual) specific combination of many different factors within the above, each itself within normal parameters that could lead to the system malfunctioning as described in my earlier post.

Barit1

If this resonance did occur and was enough to restrict the fuel flow, the frequency has to be in a range that will include the possibility of the non return valves being able to oscillate between a closed and probably fully open position. I would reckon this to be somewhat less than 10Hz but in any case far less than the likely frequency of the gear teeth meshing of the HP pump.
A far more likely source of would be the airframe vibration that is typically experienced in a final approach with plenty of flap and low airspeed. Even so, it is only the effect of this combined with the specific combination of other factors that – perhaps – could result in the fuel system going into this rather inconvenient state of malfunction.

Flight Safety

If a system such as this did go into a state of resonance, while the fuel demand remained low, adequate flow was apparently anyway maintained. Increasing the fuel demand in this circumstance however would exacerbate the difference in pressure on either side of the non return valves causing either or both the amplitude and frequency of oscillations to increase but the fuel flow to decrease as an ever increasing amount of the energy supplied by the pumps is absorbed in accelerating and de-accelerating the column of fuel within the pipes, generating shock waves and in accordance with Newton’s 3rd law, powering the reactive movements of the mass of fuel line, components and other connected structures.
As this situation developed, it is also of course very possible that the rapid changes of pressure and depression may have begun to release trapped vapours from the fuel which then begin to foam causing a further sequence of effects that have been discussed in previous posts.
The known end result is that whatever the reason, very little of the oily stuff got to the burners of the engine.

Regards to all!

JG

Green-dot

16th Jun 2008, 19:52

To Joetom,

Fuel flow could have been restricted for a long period of time.

Think of Spar or LP valve being in a position between open and closed, Engine will run Ok upto a point, but when FMV/FMU needs more flow than avail, problems will start, problems may be delayed a little with the head of fuel down stream of restriction, but problems on the way.

A spar valve in a position between open and closed most likely would have resulted in a (LH/RH) spar valve (actuator) disagree EICAS message when the actuator is not in the commanded position. A not fully open engine fuel shutoff valve would have been detected by the EEC.

Even in the very unlikely case faults would not have been detected, the most likely moment either of these valves would have malfunctioned is during engine start, the only time they are operated until they are closed at moment of engine shutdown. Both LH and RH side failing at the same time although not impossible, it is very remote.

During a normal engine (auto) start, the spar valves are opened manually by the fuel control switches and engine fuel shutoff valves are controlled by the EECs. Although the fuel control switches are manually selected from cutoff to run position, the timing of engine fuel valve opening is controlled by the EEC, it keeps the valve closed until the engine reaches the appropriate speed.

If the valves were only partially open, and if (in the unlikely event) faults were not detected by the EECs during engine start, the problems would have certainly surfaced during the takeoff roll when fuel flow is increased to meet takeoff thrust demand, a much higher demand than the thrust adjustments during final approach. A scenario for both spar valves to move away from commanded (open) position during cruise or approach has been discussed several times in this thread. Lack of evidence as to how this could have occurred prevents that discussion from continuing at this time.

Green-dot

CONF iture

16th Jun 2008, 20:14

the problems would have certainly surfaced during the takeoff roll when fuel flow is increased to meet takeoff thrust demand, a much higher demand than the thrust adjustments during final approach
Just to put some figures, we said earlier that fuel flow for flight idle should be around half liter/second and probably not far from 10x that amount for takeoff thrust ... (/engine)

ChristiaanJ

16th Jun 2008, 20:17

ChristiaanJ
Your further statement ‘…any “fuel hammer” effect is nearly instantaneous…’ is however absolutely untrue and very misleading.Point taken.

Although... I remember the F-14A prototype went down due to a similar (hydraulic system) failure on its second flight, not after x million flights/landings.

I'm still baffled by the number of holes in the cheese having to line up for this to happen for the first time.

snanceki

16th Jun 2008, 22:33

Hate to correct a correction, but according to the AAIB the difference was around 7 seconds, not only 1 sec:

Point taken.

Rightbase

16th Jun 2008, 22:45

I'm still baffled by the number of holes in the cheese having to line up for this to happen for the first time.

The farther back we take the the history of the aircraft, the easier it is to find a unique set of circumstances. So looking at the centre tank (a common feature linked to the two independent wing systems) it had a sub-zero cruise out followed by a sub-zero descent. These are the flight phases when atmospheric water enters the tank. Water scavenge does not work well below freezing, and I understand water warnings are occasionally reported when taxiing out after above-zero temperature fuel is loaded.

In this case the temperature at start-up for the return flight was below zero. If the fuel loaded was also below zero, there would be no water scavenge on take-off or climb out. The next opportunity for water to be scavenged from the centre tank would be aftert the descent to warmer levels, at which time it would be scavenged to the still cold wing tanks. Getting the holes to line up is not a problem - in fact it is a bit too easy, suggesting the holes are not big enough to bring an aircraft down.

For my money, the big question is how unusual is the history not just of that one flight, but of the history including the one before it and the conditions on the ground between the flights.

The cavitation damage statistics will be interesting. Any cavitation damage needs to be explained, because it is evidence of a fuel flow restriction at some stage of some flight. The fact that such damage is not unique to this aircraft might suggest that in this case there was just one hole too many, or the holes stayed lined up for just a few minutes too long.

The full explanation of the incident may well involve a long chain of coincidences involving more than one flight, and the investigation may take longer than usual as the correspondingly large number of alternative explanations are eliminated.

But there was no evidence of excess water in the fuel samples recovered ....

One value of different speculations about how an accident could have happened, is that it heightens awareness of how different accidents could happen.

Joetom

17th Jun 2008, 00:00

To Green Dot,

My last post only mentioned Spar Valves as an example of how a problem can exist and fuel flow through the FMU/FMV can appear normal until it causes a flow short fall. I would not expect Spar Valves to be the problem in this case, but they have caused low flow during engine operations, and yes I know EICAS/ECAM will give this info to the crew all things being normal.

My last post was just to point out that a problem/failure mode could have been lurking about long before the 38 reached Heathrow.

I'm still holding out for 1 or 2 reasons for the events on that day.

Reason 1. Leak on a fuel manifold.

Reason 2. CWT scavenged fluid into wings that had very cold fluid in them.

Both the above could start a chain of events that may fit.

The interesting points I remember are.
1. Aircraft had a cold flight to PEK.
2. Aircraft had a cold 3 hour transit in PEK.
3. Aircraft topped up wings with fuel in PEK.
4. Aircraft uplifted neat PEK fuel into CWT.
5. Aircraft had a cold flight to LHR.
6. Aircraft had little or no holding into LHR.
7. Aircraft engines wanted more flow, but was unable to provide.

Be kind to me, I'm tired !!!

Flight Safety

17th Jun 2008, 13:46

I'm not sure I see how resonance could be set up (or sustained) in this system.

First, the fuel was cold and viscous to some degree. The non return valve is one way, thus tending to cancel any resonance (which is oscillatory in nature). Resonance requires a sustained oscillation with feedback loop, and in a system that normally would not excite resonance, if one were to form under certain specific conditions, it should be easy to break up the resonance with some applied external force. Just to remind you, there were operating boost pumps and operating HP pumps here, with one at one end of the fuel "column" and one at the other end. I would think the forces of the pumps should tend to break up any resonances that might form.

I think this applies so long as a major structure(s) does not provide the feedback mechanism, which would be harder to overcome by external forces. If major structure(s) contributed to the feedback loop, then the system would display natural resonance quite readily.

I also seem to recall discussion that the non return valve is in the suction feed flow path and not in the boost pump flow path.

Water hammer (or fuel hammer) is just a pressure spike created when a valve opens or closes (due to column momentum) and is not really relavent here I would think. Water hammer (or fuel hammer) does not normally restrict flow, but is rather a design consideration pertaining to maximum pressures seen by the system.

I stand to be corrected of course.

airfoilmod

17th Jun 2008, 14:16

Not so. The function of the valve is to prevent "backflow" of the Fuel once it has passed the valve on its way to the Engine. The Valve sleeve moves in two directions, with flow (and against a spring), and versus flow, with the aid of the spring and the "backflow" of the Fuel, when it closes and prevents Fuel return. The mechanical "stop" can stall in any position, while transiting in either direction, vibrate (resonate) and completely stop Fuel entry into the system. All that is required (unlikely) is sufficient tuned energy to overcome the normal working parameters of the device.

I think some folks are visualizing the dynamic A/C system on short final without considering (perhaps) the level of energy and activity involved in landing 200 tons of incredibly powerful A/C full of PE and engines capable of lifting same. I remember my first experience watching the debut of PanAms first 747 in Honolulu. Relaxing on the beach at Sandy, about two miles from departure end, the A/C lumbered into the air "slowly". What dazzled everyone present was the sound. Everything shook from that spooky rumbling earthquake noise from the fans. the sand was vibrating on the beach.

Each of the RR engines has a fan that is probably too big to fit in one's garage, a device that can move air at a prodigious rate. Imagine each fan straining for purchase at full go, each Blade passing within a foot of the circular Fuel line around the shroud, inches from the Heat exchanger, and trying to disintegrate the HP pump. Feedback? The cold viscous Fuel in the Manifold has to resist carrying that energy throughout the system and still maintain flow within safe parameters. Resonance is definitely possible, and could easily occur given the right links in the chain. IMO.

In opposition people merely say, "Well, it never happened before."

Airfoil

"Ram". Resonance doesn't involve alot of "oscillation" My picture of Resonating fluid is a stalled stand (head), vibrating, rather asymmetrically relative to the "container". John Green might help us here.

Green-dot

17th Jun 2008, 19:34

Quoting Joetom,

I'm still holding out for 1 or 2 reasons for the events on that day.

Reason 1. Leak on a fuel manifold.

Reason 2. CWT scavenged fluid into wings that had very cold fluid in them.

Both the above could start a chain of events that may fit.

The interesting points I remember are.
1. Aircraft had a cold flight to PEK.
2. Aircraft had a cold 3 hour transit in PEK.
3. Aircraft topped up wings with fuel in PEK.
4. Aircraft uplifted neat PEK fuel into CWT.
5. Aircraft had a cold flight to LHR.
6. Aircraft had little or no holding into LHR.
7. Aircraft engines wanted more flow, but was unable to provide.

With regards to reason 1:
A leak in the fuel manifold does not explain 2 engines rolling back within 8 seconds from eachother with crossfeed valves closed and an empty center tank.

With regards to reason 2:
According to the AAIB in their bulletin S1/2008 the aircraft's fuel tanks were last checked for water in the fuel on january 15 at Heathrow; this was prior to its refuelling for the sector to Beijing. Minimum temperature at Heathrow on January 15 was 6 deg. C, maximum temp. was 10 deg. C (I have temp. records for that day).

Warm enough to drain any water collected in the tanks if transit time was long enough between the previous flight and departure to Beijing. Since fuel samples taken after the accident revealed no excessive water content, it votes for correct water sampling on January 15th and that there was no significant amount of water in the tanks when departing for PEK.

So the flight to PEK may have been cold but if the tanks were "clean" with regards to water content when departing from Heathrow, steps 2 thru 7 become less relevant.

Regards,
Green-dot

snanceki

18th Jun 2008, 05:48

Airfoilmod: The Valve sleeve moves in two directions, with flow (and against a spring), and versus flow, with the aid of the spring and the "backflow" of the Fuel, when it closes and prevents Fuel return. The mechanical "stop" can stall in any position, while transiting in either direction, vibrate (resonate) and completely stop Fuel entry into the system. All that is required (unlikely) is sufficient tuned energy to overcome the normal working parameters of the device.

Got a picture (cross section) of these specific one way valves?

Is it correct that at BOTH ends of the travel of the "restricting device" that fuel is completely shut off?

I'm more familiar with valves (spherical ball on a conical seat etc) whereby only one end of the travel actual restricts the flow.The design specifically ensures that flow is unrestricted in the other direction.

Interesting (if correct).

Two INDEPENDENT valves responding at the same time to some form of resonance (both systems likely tuned differently)...Possible but WOW!
Worse odds than the lottery!

grizzled

18th Jun 2008, 06:55

I have been following this thread from day 1. One might think that my daily involvement in the aviation safety business would mean that I would rather do other things after work than read pprune forums. Sadly perhaps -- in terms of my lack of more productive things to do on many an evening -- I find these sorts of discussions interesting and energising, sometimes even motivating me to wander off into some obscure corner of the web for hours at a time researching topics that arise from these pages.

So, here’s my comment: Over the past few years I've been directly involved in the investigation of aviation accidents and incidents, both civil and military, in diverse parts of this globe. I am certainly no subject matter expert when it comes to fuels and fuel properties but several previous incidents (and a couple of accidents) keep worming their way into my thoughts when I think of this occurrence. The cases I’m talking about have this in common: Unpredicted or unexpected changes to the behaviour, consistency, lubricity, viscosity or dispersal characteristics of fuel – caused by FSII. (Contrary to what some have written FSII is not one specific chemical formulation but can be one of several compositions, including dipropylene glycol, glycerol formal, and DiEGME.) As many of you know, the amount (if any) of FSII in the fuel loaded in China could fall into a fairly wide spectrum and still be within specs.

In serving this ball into the pprune court, I expect (and would appreciate) comments and critique on the possibility of FSII being a factor.

Grizz

airfoilmod

18th Jun 2008, 07:25

I'll look for my very old post re: Icing Inhibitors in the uplifted Fuel in Beijing. I remember suggesting Propylene Glycol, Ethanol, and Alkylates. There are some Fuel guys here and chemists too, they'll most likely be interested in your post

Airfoil

#126,#144

Mariner9

18th Jun 2008, 09:24

FSII, if present in the fuel, might be a factor. I dicussed it previously in #1292...

An interesting one, and possibly of relevance to BA038, is particulate contamination. This is measured by filtering some fuel, and weighing the particulates collected. An associated test (which forms part of the military spec) is filtration time, which specifies the maximum time for 1 US gallon to be vacuum-filtered. We have had numerous problems where anti-icing additives have been incompletely mixed, which for reasons we dont fully understand, cause difficulties in filtration. Obviously, filtration difficulties would impact on the flow of fuel through aircraft filters, and I would imagine that the effect would worsen with decreasing temperture. However, I have no idea if the subject fuel contained any FSII - chances are it didn't. I also don't know if the AAIB have had particulate contamination/filtration time checked as strictly speaking, the limits only apply at the point of manufacture. It would seem unlikely that they haven't checked this basic point however.

However, I seem to recall that in an answer to my post, someone pointed out that the fuel filters would be automatically bypassed in the event of flow restriction?

sky9

18th Jun 2008, 14:48

Am I right in thinking that this is a new bulletin from the AAIB

http://www.aaib.dft.gov.uk/cms_resources/S3-2008%20Boeing%20777-236%20ER,%20G-YMMM%2006-08.pdf

pulse1

18th Jun 2008, 15:24

As an electrochemist I have spent much of my life trying to understand technical mysteries associated with various liquids and their specifications. Based on this, when I read in the latest AAIB bulletin that the fuel "in many respects exceeding the appropriate specification" I start to ask the following type of question:

Are there some components in the fuel which have secondary benefits which have not, so far, been fully realised? E.g. lubrication. If this might be the case, then concentrating on those possible benefits might be the key to the mystery.

airfoilmod

18th Jun 2008, 15:39

I think the release updates info to include the recon of the Fuel system and to announce that Boeing are now looking for "abnormal combination of parameters." (Having found no one "hole")

It's important to reconsider that "exceeding spec." does not qualify a Fuel as "superior" in quality. It is an easy mistake to make, but "exceed" means "beyond" as well and includes a description including "poor", "misses the mark", and suggests that whatever is present in the fuel may be degrading its quality and performance.

An FP of -57C can be acquired merely by adding light molecules. Acetone freezes lower than kero, as do any number of easily added off spec matls.

johngreen

18th Jun 2008, 16:34

From the information supplied from this forum and some additional research, I understand the relevant components of the 777 fuel system to be; two AC powered centrifugal booster pumps mounted adjacent on the rear of each wing tank which feed into a common manifold. On the inboard side this manifold extends to become the cross feed (which has two normally closed parallel valves mounted only on the left side of the aircraft) and outboard becomes the fuel delivery pipework which passes through the spar valve, continues to the oil heat exchanger in the fan case and then on to the engine driven HP pump which is fitted with a recirculating bypass to control over pressure.
http://www.eatonaerospaceltd.com/fuel/Resources/021_2_Type9106boostpump777.pdf (http://www.eatonaerospaceltd.com/fuel/Resources/021_2_Type9106boostpump777.pdf)gives some details of the type of booster pump fitted.
I assume (dangerous?) that this unit is very similar to those fitted to some 747s of which I have better information. In order for it to be possible to service the pump without draining the adjacent fuel tank, a sprung loaded flap valve is located at the inlet of the pump case which is mechanically held fully open by the physical presence of the pump. On the outlet side, a similar flap valve – ie a disc with a hinge on one side perpendicular to the flow – is mounted. This is a typical non return valve which has a soft seat and a weak spring to ensure the valve will close when there is no forward flow and as far as I am aware no means of damping the movement.

Considering just the section of this system between the boosters and HP pump, any physical movement which even slightly changes the shape or concentricity of any part of the pipework also changes the internal volume of the pipe and hence introduces a degree of elasticity.
In the unwanted resonant state, a small surge of fuel progresses towards the engine where it is baulked by the HP pump which by its intended design strictly meters the possible flow. The excess energy contained in this moving column of fuel causes an increase in the local pressure creating a shock wave causing some slight expansion or lateral movement in the pipework which upon contraction returns a reflected shock wave back towards the booster pumps.
The non return valves are held open in proportion to the flow of fuel hence at engine idle the valves will be floating close to their seats. The shock wave hitting the back side of the valves momentarily forces them against the fuel flow direction and towards their seats. This causes a restriction to the flow creating a disparity of a depression on the engine side of the valve and an increase in pressure on the booster side. Once the shock wave has passed, this combined depression and pressure causes the valves to move rapidly to a more open position… causing a surge of fuel to progress towards the engine….

If the many and complex physical characteristics that are an influence allow the continuation of this feed back pattern, this system will continue to oscillate – ie resonate - until something either breaks the loop or as can also happen, exacerbate it although due to the enormous interdependent complexities involved, predetermining what will cause what response may be impossible.
It can be seen that on an increase in demand the HP pump allowing more fuel to pass might reduce the effect of the pressure build up and reflected shockwave and hence damp the effect. Alternately, the greater demand could result in the difference of depression and pressure across the valves causing them to open faster, resulting in an enlarged surge and a growth in the effect.
In the low demand situation with just a small amount of oscillation in the fuel column, the supply seen beyond the HP pump could remain quite adequate to cause no problem or alarm. If however on the increase of demand the oscillation is exacerbated, the supply will become increasingly restricted with all the energy being introduced to the system being absorbed in accelerating and de-accelerating the column of fuel within the pipes, generating shock waves and in accordance with Newton’s 3rd law, powering reactive movements of the mass of fuel line, components and other connected structures.
In this latter circumstance, a point will be reached where the suction of the HP pump causes such a severe pressure differential across the valves that the system will reach a limit where the flaps are moving with such speed and force that they will be bouncing between whatever mechanically limits the maximum open position and the fully closed positions. In this state the liquid managing to get past the valve will be a fraction of the normal full flow and at which time it becomes anyone’s guess as to the state of the fuel – or foam - between the HP pump and valve.

I have omitted a rather critical part of this explanation until now which is ‘So what caused the resonance to start in the first place? The simple answer is that in this particular case I really don’t know! However, if you can understand the explanation and visualise a horizontal column of pressurised liquid passing through a slightly open flap valve and then giving that pipe a little sideways shake perhaps you can see how easily it might start even though there are so many other parameters that have to be ‘just right’ for it to have any chance of self perpetuation.

If this overall scenario as described seems unlikely to begin with, it is made even more so by the fact that there are the two parallel non return valves on the booster pumps and for the effect to develop it is actually essential for them to react simultaneously. In the first instance this may seem absurd but they are both identical, operating close together in an almost identical environment and being induced by the same forces. Even if one valve does slightly lead the other, once even slight pressure variations begin, it is quite feasible that they would operate in perfect unison.

Rather than rewrite the details, I explained in my original post #1165 how once started, this effect could propagate from the right to the left side taking a few seconds to do so.

Still so very many holes all to have to line up…

Regards

JG

tanimbar

18th Jun 2008, 17:31

The update you refer to is a previous release, 3/2008, issued in early May.

The 16 June date on the website relates to the 6/2008 AAIB Bulletin within which is published (again) S3/2008.

I might be wrong but I can't find any changes in the two documents except someone has edited the earlier document to name it S3/2008 when previously it was called 3/2008.

Might be wrong though.

Note to myself: I must get out more.

regards, Tanimbar

lomapaseo

18th Jun 2008, 20:08

johngreen

No sense in talking about resonance unless you also include dampening (friction losses)

Forcing functions are common place, undamped resonance is not.

johngreen

18th Jun 2008, 20:29

Lomapaseo

The circumstance described is most certainly unusual but I can assure you regardless of friction losses, there are occasions when very different systems in different conditions and with very different fluids will behave exactly as I describe.

regards

JG

airfoilmod

18th Jun 2008, 20:40

fork in the road. To damp the energy within the piping, absorbers,(damped mounts) must be tuned for all forseeable mechanical vibration. To that extent, a certain flexibility needs to be engineered into the mounting of the piping. But wait, if there is too much, the Pipe and Fuel can act in unison, which would conceivably block flow. So what is the design of the pipework relevant to the contained and flowing Fuel? And let's not forget forces other than resonance. Like Harmonics, Flutter, coef friction values dependent on fuel type and source. This is getting interesting.

Airfoil

At the point of entry of this discussion, system isolation and ETOPS are frankly irrelevant. Two systems on separate A/C could behave identically with one another given the ineluctable power of certain anomalies and reasonably similar parameters. Lose the seductive and nonrelevant impetus of ETOPS, or lose the basis of debate. This isn't about how incredible it is to entertain the thought of concurrent failure anymore, it is a given.

Carrier

18th Jun 2008, 21:24

Is it a fair observation that more engines would not be the solution? If there were four engines would all four give inadequate power with the same outcome?

airfoilmod

18th Jun 2008, 21:39

as it may seem. If two heretofore simultaneous failure proof systems have just failed, and not due to all the engineered in safety of ETOPS, then the answer is no, twelve engines would have failed the same way. Isolation from bowser to chox is possible (At ridiculous cost), so by definition we're dealing with a non Etops issue.

My mentor and his co-pilot ate the same pork sandwiches on their way to bomb Tokyo in 1945. Both got food poisoning and were unable to fly. The chicken sandwich got ate by the navigator, who was an eager ab initio student on the way back. Separate everything for each side on the ETOPS twin? Ouch, you think Fuel's expensive.....

Airfoil

trashie

18th Jun 2008, 22:41

At a recent safety conference attended by a Boeing accident investigator, it was revealed in social discussions that Boeing had failed to find any mechanical, environmental ice, or other aircraft malfunctions as causal factors, however, have attributed the malfunction to interference with the fuel pump electronics from a laptop computer being operated against airline rules by a senior British government official over the top of the area of the pumps.

propaganda

18th Jun 2008, 23:00

I doubt that theory, as no Senior British Gov't official would be sitting that far back in the cabin.

CONF iture

18th Jun 2008, 23:36

HP fuel pumps are mechanical ... not sure there is any electronic involved (?)

Rightbase

19th Jun 2008, 00:16

Hmm....
Silly late night thought. If senior government officials could be persuaded to sit directly above the high pressure fuel pumps it might solve some of our other problems.

barit1

19th Jun 2008, 02:40

HP fuel pumps are mechanical ... not sure there is any electronic involved (?)

I'm 99% certain the reference to "interference with the fuel pump electronics" must really mean EMI to the FADEC. However that does not explain the fact that the fuel metering valves were commanded open, but fuel actually delivered was a fraction of the demand.

airfoilmod

19th Jun 2008, 03:08

Restriction between heatexchanger and FMV would explain both HP high side cavitation and no additional flow at valves; similar result if restriction was the H/E or prior. Not a "Pull" problem but a "Pack" problem.

arcniz

19th Jun 2008, 07:27

I find it very gratifying to see so many informed and thoughtful people putting their heads together on the "outside the box" analysis underway. In the worst case, this discourse burns some time but stimulates flexible thinking about things that others might readily accept as "status quo". In the best case it may allow or inspire people in the official determination loop (and in the aircraft systems development stream) to work a bit harder at understanding the outer margins of probability for failure in the marvelous products they devise.

Comment on two recent posts:

at # 1375, PickyPerkins says:
The engines on the 767 performed just fine in suction all the way from sea level to 41,000 ft.

What they could NOT handle was a cessation of boost pressure during the climb.
The engines spooled down 14 seconds after the boost pumps were turned off.
.... gap ....
This seems a clear indication to me that the boost pumps were doing something which the HP pump could deal with so long as boost pressure continued.
But when boost pressure was discontinued, the engines spooled down after a delay of 14 seconds.

That something which boost pumps were doing could have been bringing air out of solution.
Which was OK with boost pressure on, but not OK when the boost ceased.

I would suggest that your concept is very promising, but the conclusion is incorrectly stated:

The effect of the submerged boost pumps running will be to keep dissolved gas IN solution, because the pressure gradient across the pump is relatively gradual (with fluid present at both inlet and outlet) and the pressure added by the pump is not so large an increment to the gravity feed pressure of the surrounding fuel.

If, however, the boost pump ceases operating, then a larger pressure gradient develops at its outlet side due to the suction of the HP pump and engine. This increased suction pressure gradient would likely be the cause of dissolved and otherwise entrained gasses increasing in volume and coming out of solution in a way that might disrupt the overall flow.

-------

Johngreen's detailed explanation of resonance is very informative as a baseline for discussion.

My understanding is that the resonant couple in a plumbing system like the 777 fuel supply path includes at least the two normal tuned systems, plus possibly other parasitic resonances. A first tuned/resonant path is the plumbing, pipes, etc, and the terminations formed by pumps and gates and valves. A second is the fluid, gas, or whatever may be rattling around inside the plumbing. Outside structures and forces may contribute to additional resonant loops.

A teasing difference of circumstance in the BA038 context is the history of very cold fuel. Someone has credibly noted that JPxx fuel viscosity is characterised only at -20c (iirc) in the standard fuel spec, meaning the viscosity might differ widely with varying fuels in the regions above and below -20c. Clearly, fuel viscosity will affect flow characteristics as well as the propagation velocity for shock waves (which controls resonance behavior). Could it be that the very cold fuel temps changed viscosity of a somewhat non-common fuel in such a manner as to put the resonance propagation velocity characteristics of the fuel outside the range of modeled behavior used in the 777 design calculations, and therefore outside the damping ability designed into the system?

If low temps, uncommon fuel, and resonance possibility were factually linked to the chain of causality, one might have a very plausible failure mode.

Flight Safety

19th Jun 2008, 16:32

I'm not sure I accept the resonance theory, but for the sake of discussion....

Years ago I once had a hot water shower faucet that resonated. It would start as the water got hot (temperature induced). The typical screw type faucet was many years old and the screw stem part was worn. When the resonance started, the rubber part of the valve (at the end of the stem) would oscillate from open to closed to open again on the valve seat. When the resonance occurred, the water flow would reduce (the valve being closed part of the time). I assume the hot water made the copper pipe flexible enough to allow the resonance to start. Naturally the resonance would occur at the moderate setting appropriate for a nice warm shower (if you held the handle with your hand the resonance would stop), which meant the valve had to be open or closed more to stop the terrible noise (resulting in a too hot or too cold shower), so the valve being open a certain amount contributed to the resonance. The fix was to replace the worn faucet with a new one (where the stem would not move and thus would not resonate).

Now to this accident.

There was no flow bypass in the shower example (which would have prevented or damped the resonance and provided alternate flow), and the energy feeding the resonance (since all resonances have losses) was the available water pressure. In the 777, we have 2 fuel pumps on each wing (boost and HP) capable of providing the energy to sustain a resonance. My question is in a 777 fuel system, do we have a valve in a common un-bypassed path between the tank and HP pump, that can restrict flow fuel if driven open and closed by a resonance?

airfoilmod

19th Jun 2008, 17:34

I think it important that other sources of energy be considered. Resonance is intriguing, and damping the pipes, etc. The energy provided by Boost and HP is substantial, but more than this, consider the introduction of massive vibratory and sonic input from core and fan. This is what happened, by report, (Initially responded....). A cold and viscous fuel in a slow, low energy green state is assaulted by enormous and rapid changes, locally, and we talk about tap water? A "length" of contained fuel may not react well to local insult of 35k kg of thrust and all the intricately timed reactions inherent in the system. Envision a long narrow mass (fuel), vibrating (in sequential expressions relative to its proximity to the energy source) and ponder what all the vibration is doing to its mass, and include sonics, flutter, (valves), etc. It is not for nothing Boeing has assembled the entire fuel system at test.

Airfoil

Re-Heat

19th Jun 2008, 17:51

Interesting that modern, greater precision could result in more accidents (similar perhaps to the greater navigation precision we see today that heightens danger to aircraft flying on the same airways through the airway centreline rather than scattered through the airway).

The implication is such that ever greater precision is not desirable, and requires exponentially greater understanding and testing of the small defects that arise now the larger, obvious defects have largely been solved...

pls8xx

19th Jun 2008, 17:57

If the oil heat exchanger is located in the pipe network of only one side, then the separate systems are not mirror images of each other. Similar resonance to dis-similar systems at about the same time is highly unlikely.

grizzled

19th Jun 2008, 18:08

Your view is one that, I think, will be repeated and strengthened over the next few years. Although it may contribute to "thread drift" I must opine that you have identified what I believe will become the prime aviation safety issue of the next decade.

lomapaseo

19th Jun 2008, 19:09

Re-Heat

--------------------------------------------------------------------------------

Your view is one that, I think, will be repeated and strengthened over the next few years. Although it may contribute to "thread drift" I must opine that you have identified what I believe will become the prime aviation safety issue of the next decade.

Agree. but only when we have acheived a factor of ten reduction in accidents due to the more obvious causes (excluding BA038.)

Re-Heat

19th Jun 2008, 19:21

It almost makes one wonder if insertion of random, minor, marginal measurement and specification errors throughout a precision construction process would be desirable (thinking again back to the airway precision debate where random lateral offset - though still within the airway - is in current thinking).

I hastily add that I should probably patent this idea.

ChristiaanJ

19th Jun 2008, 20:02

Re-Heat,
You may have a point.....

Remember the static test on the A380 wing that broke at something like 148% of design load, rather than 150%?

Maybe, sometimes you would like to have that little bit of extra margin, because they did not mill out every single "superfluous" ounce...

Might be worth discussing, although it's more academic than anything else.
Accidents due to this kind of extremely rare combinations of circumstances still happen, agreed.

But as long as third-world airlines dump badly maintained aircraft in atrocious circumstances with a frightening regularity.... I think our priorities are elsewhere.

airfoilmod

19th Jun 2008, 20:16

Having to do with mirrored and duplicative systems (Fuel). has been addressed elsewhere also. In perfecting more and more dependable systems, the Human side of the equal sign becomes more and more..... Dependent. ETOPS must for purposes of economic feasibility, divert from isolation and engineered anomalous design to make more and more infrequent, the failures which challenge the philosophy. There is a definite difference between redundancy and anomalous isolation. Redundancy merely provides two systems to fail under similar circumstances; heterogeneous engineering separates the systems in ways that "prevent" mirrored fault.

Airfoil to Re-Heat: it's called engineered anomalous design.

As I offered before, 038 isn't about Etops, instead its about vulnerability of separate and equal systems.

Green-dot

19th Jun 2008, 20:18

trashie:
. . . .have attributed the malfunction to interference with the fuel pump electronics from a laptop computer being operated against airline rules by a senior British government official over the top of the area of the pumps.

propaganda:
I doubt that theory, as no Senior British Gov't official would be sitting that far back in the cabin.

CONF iture:
HP fuel pumps are mechanical ... not sure there is any electronic involved (?)

barit1:
I'm 99% certain the reference to "interference with the fuel pump electronics" must really mean EMI to the FADEC.

I assume trashie is referring to the boost pumps, not FADEC or HP pumps. If so, the pumps themselves are outside the hull (which functions as a Faraday cage) and very unlikely to have been affected.

Regarding the (pumps) electronic component locations relative to the mentioned seating position of the "official with his laptop", he would have been nowhere near any of those components if you know the T7 well enough.

Suppose the pumps were affected (highly unlikely), what effect could there have been? Stop the pumps? Suction feed would still feed the engines. Or make the pumps (3 phase AC) somehow run in a reverse direction . . . .and then all four of them at the same time with their LH/RH electrical circuits well separated? Again, highly unlikely.

If there is any substantiation in what the accident investigator discussed, the scenario could fit uncommanded transit of both spar valves. More holes in the swiss cheese had to have lined up though before such a scenario with a laptop could be considered as plausible.

Regards,
Green-dot

ChristiaanJ

19th Jun 2008, 20:42

At a recent safety conference ... it was revealed ... that Boeing ... have attributed the malfunction to interference with the fuel pump electronics from a laptop computer being operated against airline rules by a senior British government official over the top of the area of the pumps.The loud laughter and hilarious applause following this "revelation" have been edited from the tape in question.

johngreen

19th Jun 2008, 21:36

pls8xx

Keep up! Just to clarify the 777 fuel system, there are two booster pumps each with a non return valve located at the rear of each left and right wing tank. Each pair of pumps delivers fuel independently (unless the cross feed valves are opened) to its respective engine each of which is fitted with a heat exchanger and each with a mechanically driven HP pump.

Flight Safety

Your experience with the shower is a perfect analogy to the effect I have described.

The booster pumps are centrifugal and will operate constantly at their rated speed even when no fuel is actually being consumed as will happen for example during the initial stage of engine starting. As the resistance to flow is decreased, the volume of delivery will increase and the delivery pressure decrease accordingly. (A graph indicting values is on the catalogue for those interested).

The HP pump has to be a positive displacement pump – for example a vane or gear pump – such devices being able to produce the much higher pressures required for the burners. Regardless of the boosters trying to always deliver their maximum possible output, the HP pump will only allow a fixed amount of fuel to pass for each shaft revolution, the rotational speed being determined by its mechanical connection to the engine. It is this then that offers the restriction to flow that permits the build up of pressure fluctuations having the effect in this circumstance of being a valve that is opened or closed against the delivery from the booster pumps in accordance with the engine fuel demand.

Although it does not affect the resonance scenario, the HP pump is also fitted with a bypass arrangement. By this, the pump will always be delivering too much fuel for any given engine speed, the excess being recirculated in the vicinity of the pump. This also allows the pump to pressurise the engine fuel system against the closed fuel valve during the start procedure when the pump has no option to rotate with the engine although no fuel delivery to the burners is yet required.

Ailfoilmod

Enjoying your mind stretching additions. I keep reflecting on the possible pressure waves and other dynamics that might have been dancing together in the remaining bulk of fuel in those drum like fuel tanks…

Re-Heat

Exploring this incident - among others - I also have many thoughts about the relevance of precision on safety. It remains for me that if we were really meant to fly our bodies would be formed with wings, a tailplane and something hopefully more akin to a Merlin than a flat Lycoming between our legs. Having a personal lack of such equipment, given the choice, I think I would anyway still tend to choose the safety of today’s imperfect machines over too many adventures being carried aloft in the likes of the Doves and Herons of my youth. The fallibility of the human controller(s) nevertheless probably remains a greater threat than the fallible machine.

Regards
JG

Machaca

19th Jun 2008, 21:36

1. Low Pressure boost pump in wing tank, output is "constant"
2. Low Pressure - engine driven, output is direct relationship to engine rpm
3. High Pressure - engine driven, output is direct relationship to engine rpm

http://img83.imageshack.us/img83/8171/777fuelpw3bww3.th.jpg (http://img83.imageshack.us/my.php?image=777fuelpw3bww3.jpg)

http://img75.imageshack.us/img75/3083/777engineug1bli7.th.jpg (http://img75.imageshack.us/my.php?image=777engineug1bli7.jpg)

Low inlet pressure to the HP pumps is a focus of the investigation. There's a lot of cheese slices between the fuel tanks and HP pumps!

Harmonics? Perhaps.

Beyond FCOC and fuel tubing atheromata, I'm suspicious of excessive Prerotation and Backflow (http://caltechbook.library.caltech.edu/22/01/chap4.htm) of unusually cold & viscous fuel reducing output of all the low pressure pumps.

An increase of intake vortices at the wing tank boost pumps may have been exacerbated by relative fuel surface level changes in relation to the pickups due to aircraft pitch changes during approach.

http://caltechbook.library.caltech.edu/22/01/figs/fig408.jpg

http://caltechbook.library.caltech.edu/22/01/figs/fig406.gif

-=MachacA=-

Re-Heat

19th Jun 2008, 21:53

I wouldn't suggest a return to past, inherently dangerous designs would be desirable!

airfoilmod

19th Jun 2008, 21:54

might involve the HP packing viscous fuel into the nozzle annulus and/or the bypass (relief circuit) while the Low side simply couldn't keep up. At this point the fact that the LP's were active would RESTRICT free flow, the alternative of suction being locked out. At some location (bearings at high side) is where the Fuel "Sheared" into dense "petals" and "voids" (cavitation). Alone, I think cavitation was insufficient to choke the supply, but briefly. At this point (when the Engines were ~1.57 EPR), I believe the coup de grace may have been introduced into the supply with an as yet undetermined combination of Resonance, Harmonics, flutter (at LP valves), and an inability of the system to "select" suction or boost. The reason I'm keen on flutter is that it would explain a halving of fuel flow during the time its cycle was "closed", against the LP port.

Re-Heat: A little too cryptic for me, sorry

rgds Airfoil

ChristiaanJ

19th Jun 2008, 22:11

I wouldn't suggest a return to past, inherently dangerous designs would be desirable!Point taken.
However, being jumped on by the bean counters because it broke at 152% is not ideal, either....
Should probably be discussed somewhere else, because it's an interesting notion.

Flight Safety

19th Jun 2008, 22:34

Or it could be that when the fuel flow rate increased with the power increase, something got sucked into the pickup screens (that later disappeared) thus reducing the flow and was held there by the suction until impact. In theory this could fit the facts as we know them.

How many fuel pickups are there per tank, 3?

airfoilmod

19th Jun 2008, 22:40

posit feels nearest the fact given the Data. Restriction in the form of ice crystals was mentioned by D. Carbaugh, Boeing Chief of Safety Pilot. The restriction of the Fuel itself, as a too viscous mass or a too energetic mass, full of pressure waves and other considerations, all are important to explain the low fuel supply at HP.

Machaca, thanks for the visuals, great help.

Airfoil

Flight Safety

19th Jun 2008, 22:48

Yes, thanks Machaca.

It looks likes there are 3 fuel pickups for each tank (left and right). Each of the 2 boost pumps (per tank) has it's own pickup, and the suction feed has it's own pickup. So nice redundancy for fuel pickups, but this means 6 fuel pickup screens would have to be blocked, all at nearly the same time for this scenario to be the culprit.

airfoilmod

19th Jun 2008, 22:58

makes a more reasonable solution one that isolates one or two crooks or crinks, but those needing to be vulnerable to the cause of fault. And vulnerable in the sense of simultaneous failure (~8 secs.). I look suspiciously at FCOC, and the plumbing around it. What a swell place for ice crystals to cascade into a clump and choke the life out of our A/C. Or like a cocktail shaker to block flow due to agitation and foaming. Boeing has the answer in the test cell(s).

Airfoil

Flight Safety

19th Jun 2008, 23:07

The problem with the FCOC is heat is transferred from the oil to the fuel. This would seem to reduce our chances for ice formation between the LP pump and HP pump. Further, we haven't heard anything about any possible ice damage to the HP pump, only suction cavitation damage.

I don't know, maybe the fuel was as thick as mallases.

What's interesting is that both engines rolled back to virtually the same power level, EPR 1.03 and EPR 1.02. So not only did the restriction or obstruction occur at virtually the same time on both sides of the airplane, but the amount (quality, quantity) of the restriction was virtually the same on both sides. I'll bet the suction cavitation damage is virtually the same on both HP pumps as well. I wonder if maybe Re-Heat is on to something here.

airfoilmod

19th Jun 2008, 23:34

had to have been a transient, and fuel related. Scrapers, plastic, condoms, not possible, the block was a phantom, then a plug, then a phantom. What type of material would flow just fine at green descent, flow more slowly as flow and pressure increased, then mimic a solid, resisting all power and pumps to get it to move along. A change in phase? likely. A change in viscosity? easily. How about a change in energy content. John Green? (not caloric, but entropy)

Flight safety, I'm glad you brought up Oil Cooling. A thin oil, jet lube does not do well in very low temps. Fortunately it can be cooled by fuel, but wait, we need to heat it. Congealed oil in the cooler? Subject to convective cooling by the airstream at -70? Why should frozen oil bother 038? There's plenty left in the case. But if some is locked up in the FCOC and further cooling the fuel, well that's a horse of a different hue. Temps in the cooler? energy at 1.57EPR in the cooler. Where is the bypass? Does it matter? Who needs ice when the temp in the FCOC is -70C? Thaw? sure, give us twenty minutes. Pure speculation.

Flight Safety

20th Jun 2008, 16:15

Whatever the restriction or obstruction was, it was very consistent on both sides of the airplane. This should be an important clue because with this kind of consistency (on both sides of the airplane), this should a reproducable failure (since it already occurred twice the same way, on both sides of the same airplane).

Flight Safety

20th Jun 2008, 16:34

I have another idea.

I noticed looking at the drawings supplied by Machaca, that all 3 fuel pickups are located next to what appears to be a bulkhead between the main tank and the center wing tank. Since the center wing tank was basically empty at this point in the flight, what would the temperature of this tank have been? If this empty tank was colder than the fuel in the main tank, how would this have effected the portion of fuel in the main tank located right next to the bulkhead (where the fuel pickups are)?

airfoilmod

20th Jun 2008, 17:23

I think for there to have been a double failure so close in time, it's necessary to look for areas where parameters would be fairly close in range. The Spar valves shut at the same time could initiate cavitation but would make both environments (fuel lines) dependent on the "same" "set" of conditions. The volume of the lines, though similar, would have been susceptible to varying results from suction due to connections, tubing strength, indeed even the "position" of the valves themselves.

When I think of cavitation, I visualize a smallish tightly sealed space subject to great energy at one end and collapse close by (shear). I'm looking for a block close by the HP's, one that reacted to parameters present in spite of all engineered precautions and anticipated challenges.

On the other hand, the delay of 7 seconds could represent the "differences" in systems' reactions to the fault: partial "collapse" of the piping to fixed values, time for two spar valves to close completely having lagged, run up of the lobes of the HP's to max, all other junctions to reach maximum deflection due to demand, etc.

Question: Could cavitation itself have been responsible for loss of commanded power and failure to respool? Only in the sense that it represents the "onset" of fault, the plug would have been responsible for the transition from "cavitation as evidence" to starvation and ongoing low power. 1.02 and 1.03 EPR mean not much is happening in the thrust department.

FS: I think the empty center tank would have performed more as an insulator than a chiller. Think Thermos.

Green-dot

21st Jun 2008, 12:23

Posted by airfoilmod:

The Spar valves shut at the same time could initiate cavitation but would make both environments (fuel lines) dependent on the "same" "set" of conditions. The volume of the lines, though similar, would have been susceptible to varying results from suction due to connections, tubing strength, indeed even the "position" of the valves themselves.

There may have been a time lag between the two spar valves closing, either at initiation or in travel time. One valve may have been slightly faster than the other. Depending on what hypothetically would have caused such an anomaly, one valve may have closed further than the other before restoring to normal condition.

When I think of cavitation, I visualize a smallish tightly sealed space subject to great energy at one end and collapse close by (shear). I'm looking for a block close by the HP's, one that reacted to parameters present in spite of all engineered precautions and anticipated challenges.

Not necessarily so. Remember the engines were initially accelerating, demanding a considerable increase in fuel flow. Sudden deprivation of demanded fuel feed, depending on timing and rate of the reduction reaching the HP pumps could lead to the same results.

On the other hand, the delay of 7 seconds could represent the "differences" in systems' reactions to the fault . . . .

Fuel lines (LH and RH) between the spar valves and the engines are similar and almost a mirror image of each other. From the spar valve the fuel line initially runs parallel to the rear spar and then makes a 90 deg. turn forward following a rib then bends slightly inboard before making another turn outboard then forward and inboard again (going around the drybay) before finally going relatively straight forward, entering the engine pylon and finally going downward connecting to the engine fuel line. Viewed from the top the fuel line path roughly represents a Z shape followed by a U shape (around the dry bay) and then straightening out into the pylon area.

However, (depending on many "ifs" yet to be answered) if the spar valves were affected in the way i described at the very beginning of this thread, it should not be ruled out that the APU fuel shutoff valve (and perhaps the APU remote shutdown) electrical circuitry was also affected. If the valve was electrically opened in the same action the spar valves were closing, all of the fuel lines between (partially closed) spar valves (closed Xfeed valves) and boost pumps in the fuel feed manifold of the LH fuel system could have been acting as an accumulator providing just that much more buffer in feeding the LH engine before rolling back 7 seconds later than the RH engine did? The APU fuel supply line is a very long line going to the tail before ending at the APU fuel control unit. With a system out of wack, that APU fuel control would probably have continued to shut off fuel supply to the APU. Just as a reminder, there is still no official answer as to why the APU door was in the open or partially open position at "touch down", of which there is photographic evidence.

FS: I think the empty center tank would have performed more as an insulator than a chiller. Think Thermos.

An empty center tank filled with air and fumes will adjust faster to ambient temperature than a main wingtank (partially) filled with cold soaked fuel. Furthermore, the center tank temperature is also affected by the heat radiated from the airconditioning systems directly below the center tank.

Green-dot

precept

24th Jun 2008, 21:57

Given the continuing interest in this accident, the following URLs are links to the US FAA reporting site. Interested parties can access the site and drill down on the current status. The names and positions of US investigators are identified on the first site.

We continue to await governmental, industry and knowledgable individual insight into this potentially catastrophic incident. When you get to the page, click on "factual" PDF page for most complete information.

DCA08RA028 (http://www.ntsb.gov/ntsb/brief2.asp?ev_id=20080117X00065&ntsbno=DCA08RA028&akey=1)

http://www.ntsb.gov/ntsb/GenPDF.asp?id=DCA08RA028&rpt=fa

lomapaseo

25th Jun 2008, 13:58

precept

When you get to the page, click on "factual" PDF page for most complete information

Where:confused:

soem dood

25th Jun 2008, 14:13

The NTSB site layout is not too intuitive and it's search function is spotty.

Here (link) is a place that you can find all NTSB work-product on foreign investigations, just look for G-YMMM. However, there is really nothing new in there.

NTSB - Aviation - Foreign Investigations (http://www.ntsb.gov/ntsb/foreign.asp)

If you suspect there is something in the official docket, but not shown on the website, then you can make a request for that record here:

http://www.ntsb.gov/pubmail/pubmail.asp

paulrcgb

29th Jun 2008, 08:34

Sorry to ask the question...did anybody (bar the BBC) ever see or find a url to the BA internal report? thx

777fly

1st Jul 2008, 19:01

Hot rumour at LHR this morning that there has been another 777 engine roll-back.

Swedish Steve

1st Jul 2008, 19:26

More than a rumour. One engine failed to respond to throttle demands in cloud. Other engine OK. Both OK when leaving cloud.
Sorry don't ask, thats all I know.

DILLIGAFF

1st Jul 2008, 21:02

Happened last Sunday a/c MMC. Whilst at F/L 370 engine did not respond for 90 seconds. Aircraft is still at LHR, AAIB have inspected it.
D

Mat Sabo

1st Jul 2008, 21:45

Can bigots pin this on contaminated Chinese fuel again? If so many will be clamouring for the boycot of the PEK Olympics........danger!!!!

Green-dot

1st Jul 2008, 22:02

DILLIGAFF,

Thanks for the details.

Here is an interesting article which may be related to this latest incident:

High Altitude Engine Flame-Outs | AVIATION WEEK (http://www.awgnews.com/aw/generic/story_generic.jsp?channel=bca&id=news/bca0707p1.xml&headline=High%20Altitude%20Engine%20Flame-Outs)

PS. Apparently asking a few simple questions about altitude and flight phase, just prior to your post, was reason enough for the mods to remove my post? :=

Regards,
Green-dot

DILLIGAFF

2nd Jul 2008, 03:10

MMC incident was caused by ice crystals forming on TAT probe as A/C flew through cloud leading to a false reading. When A/C came out of cloud ice melted and fueling returned to normal engine throttled up as requested.
By the way the F/O was John Coward.
D

wilyflier

2nd Jul 2008, 09:57

Lucky Coward,
Arent those pitots heated ?

......Was that stuff about high engine ice in strange forms by Prof/Doctor Viellette, (Aviation Week last year) promulgated to all working Aircrew?
.......It seems essential information to me, and should have been shown up in this BA 777 thread at the very beginning by one of you current Captains.

.......I had a reliable report last month of CB up to 80,000 ft in USA . ......... I have seen thin anvil stuff 100 miles ahead of an actual CB-and got iced up pitots at 40,000
(pitot heat working, 3 aircraft lost ASI)

Oluf Husted

2nd Jul 2008, 23:00

Dear Green-dot,

Thanks for the article: "High Altitude Engine Flame-outs" that tells us, we have been flying around not knowing the hard facts about engine icing. And that we still do, since advanced testing is still taking place, also in 2009.

Green-dot please reread our exchanges from may 1. and 2. 2008 in this tread, "your" article just sharpened my theory:

"That engine core icing was the reason for the BA38s engines hesitation"

Oluf

lomapaseo

2nd Jul 2008, 23:30

While I appreciate the latest news about possible engine icing at altitude, I do not believe that it has been linked in any fashion to the BA038 event durring an approach phase at non-icing conditions.

If the speculators and theorists among us want to discuss this aspect then I think that it needs its own thread or else a positive link via the AAIB

Oluf Husted

3rd Jul 2008, 08:22

Dear lomapaeso,

It was indeed: "Icing condition" during the last 10 minutes of BA38s career.

Ground temperature was +11 degrees C. and its RR engines flew in and out of broken clouds.

Boeings definition of "Icing condition":

Anytime the OAT (temperature) is below +10 degrees C. in moist air (dew point within 3 degrees C.)

And the higher the temperature, the more severe is the icing condition, due to the higher cloud water contend.

Read more about it here: www.whistleblowers.dk

Oluf Husted

punkalouver

3rd Jul 2008, 13:53

Service experience generally indicates that turbine engines are not susceptible to mixed phase or glaciated icing conditions, with the possible exception of two known potentially vulnerable engine design features. These two design features are (1) pronounced inlet bends (such as particle-separator inlets), or inlet flow reversals, where inlet flow can stagnate and accumulate ice, and (2) high solidity dual row front stage compressor stators that can be susceptible to non-aerodynamic ice buildup on the stator airfoils resulting in core airflow blockage. These two design features should either be avoided or carefully scrutinized by analysis and testing to assure their non-susceptibility to mixed phase or glaciated icing conditions.

I know it is a bit off topic but which jet engines fall into thise two categories?

ChristiaanJ

3rd Jul 2008, 14:43

In category 1) I would think you'll find engines such as helicopter turbines, some turbo-props, and some ancient engines with centrifugal compressors.
Not sure about category 2)

arcniz

3rd Jul 2008, 18:49

Can bigots pin this on contaminated Chinese fuel again?

The poster's highly emotional comment, and the underlying concept, are misplaced here.

A number of reasonable persons consider fuel a likely or at least possible cause for the power failure because it is one of the few critical elements in common for both turbines on BA038.

Quite early in the post-incident investigation, the investigating authorities clarified that the fuel was not obviously 'contaminated' . Some people see as possible, however, the concept that the fuel might have met all prevailing specifications and still might have had some property differing from other "normal" supplies in common use, thereby defining an uncommon circumstance that might help explain why 038 uniquely had a problem.

The aviation community is international and very cosmopolitan. In regard to matters of safety, the focus is on finding answers and preventing future failures. While individuals may have their own biases, the consensus interest is directed toward empowering safe and reliable global aviation for all parties and all nations - not looking for persons or places to blame.

This is clearly not fertile ground for bigots, so please try to get a grip on yourself.

ChristiaanJ

3rd Jul 2008, 20:17

Can bigots pin this on contaminated Chinese fuel again?
arcniz already has mostly answered this...

bigots? Haven't really seen any here. Some far-fetched suggestions, yes, but that's what R&N is all about.

contaminated ... fuel? It already seems to have been established the stuff wasn't contaminated.

... Chinese fuel? Maybe the particular 'cut' of fuel may end up having some relevance, although it sounds less and less likely. Tons more of the stuff were uplifted on the same day from the same place, and nobody else ended up just short of the runway.

... again.? The venom is in the tail. When did this happen before?
In short, I think we can class this one as a wooden-spoon-stirring post.

Far more interested in the ice accretion discussion.
As a non-engine engineer, I thought compression heated the air.
So with an OAT of about +10°C, wouldn't any earlier ice have melted rather promptly, once OAT was over 0°C?

Green-dot

3rd Jul 2008, 20:27

Dear Oluf,

Having re-read our May 1st and 2nd exchanges i can see (as i did then) your point regarding core icing. Although i keep several options open to the cause of the BA038 accident, the AAIB reports so far reveal no indications that engine icing is suspected. The AAIB specifically stated in the S3/2008 bulletin, released in May (after our exchange), that there was no evidence of core engine icing and that the reduction in thrust on both engines was the result of reduced fuel flow and all engine parameters after the thrust reduction were consistent with this.

To my knowledge, if an engine rollback was caused by core icing, EGT would have increased (with fuel flow required available). Quoting the article on "High Altitude Engine Flame-Outs":

"Incident investigators using data from DFDRs found that the uncommanded thrust reductions were manifested initially by a gradual decay in fan rotation speed and a final stabilization of the engine at a sub-idle operating condition. The engine speed decay was also associated with an increase of turbine gas temperature and a failure of the engine to respond to movement of the throttles/thrust levers. The term "rollback" has commonly been used to describe this condition."

The recorded engine parameters, according to the AAIB, do not show high EGT readings consistent with possible core icing. However, not ruling anything out before the cause has been substantiated by facts, could BA038 have flown anywhere near thunderstorm anvils along its route that day, possibly accumulating ice consistent with what has been described in the mentioned article? I assume the AAIB will have looked into that possibility?

I do not rule out your theory. Although the rollbacks occurred at low altitude, ice accretion could have commenced at high altitude near TOD, keeping compressor temperatures low enough during the CDA for more ice to accumulate at lower altitudes. If so, the recorded engine parameters revealing the contrary, will have to be explained.

Green-dot

boguing

3rd Jul 2008, 20:38

Technically speaking, ice (water) doesn't thaw until +4 Deg Celsius. But I know that you knew that! Pedant mode off.

chris weston

3rd Jul 2008, 23:09

The idea that water ice does not change phase ie thaw until +4C is simply wrong.

This is basic Second Law of Thermodynamics stuff.

Water has an equal probability of solid and liquid phases at 0 degrees C under standard (we can argue) conditions of T&P or, more accurately, the Entropy Change ("Delta S Total") is zero at 0 degrees C under standard conditions of T&P say 101.3 kPa et al.

Yes yes that means the Gibbs Free Energy Change Delta G is zero too.

Shifting the parameters of T & P will simply shift the position of the equilibrium.

At any temperature > 0 degrees C, including +4C, the probability of liquid phase water existing represents a positive entropy change over that of solid phase water. ie Liquid is more probable.

In simple language ice melts at > 0C and it's crucial to grasp that there is no single "switch temperature", its a continuous shift in equilibrium position and probability that's going on.

Do the sums, try different values.

Delta G = Delta H minus [T(in Kelvin) x Delta S of the particles]

Or if you prefer

Delta S Total = Delta S of the Particles plus Delta S of the surroundings.

Delta H Fusion water is +6 kJ/mol
Entropy of Liquid phase water is 63 Jk–1 mol –1
Entropy of Solid phase water is 41 Jk–1 mol –1

CW :)

Dated1

4th Jul 2008, 14:33

Just before impact the aircraft was seen to have an unusaly high angle of attack.
Assuming the aircraft was in a dead stick 'glider' approach should the pilot not have lowered the nose to gain airspeed and would not the subsequent ground effect have extended his glide path?
Trying to maintain height and extend glides by subconsiously pulling back on the stick is an extremely popular way of taking pilots out, as we all know.
Has this pilot's perfomance at the time been evaluated as a part of the air accident investigation?

Shaggy Sheep Driver

4th Jul 2008, 14:43

I think he may indeed have lowered the nose when the power faded, to keep the aeroplane flying and reach the field (I think the captain may also have removed the 'drag flap' as well?), then pitched the aeroplane up at the last minute, very close to the ground to dissipate as much energy as possible, resulting in a high-ish rate of descent at minimum forward speed for the last few feet?

Seems like a job well done to me.:ok:

aviate1138

4th Jul 2008, 14:49

No one was killed, barely anyone injured, the 777 missed the obstruction [lights/localizer?] on the approach by 15/20 feet. What more should the handling pilot have done? The undercarriage dug into wet ground and absorbed huge amounts of energy and everyone walked away.

Maybe if he had [being incredibly wise after the event!!!] extended the glide, would he have contacted the tarmac, causing sparks and maybe a huge conflagration, possibly engulfing the fuselage and exiting likely to have been much more hazardous.

Aeroplanes are not people and aeroplanes don't have grieving loved ones left behind.

BOAC

4th Jul 2008, 15:17

Correction to Oluf's post #1456 - Boeing look at engine icing on the basis of TAT, not OAT, so although 038 may well have been in 'engine icing conditions' during the descent, that would have been due to TAT.

Also to say that some of us (pilots) are aware of engine icing risks above 'normal' altitudes. Boeing say one can ignore engine icing with a SAT of -40C or below unless throttled back. I have been somewhat more cautious than that for some time and I suspect that 'rule of thumb' may change.

petermcleland

4th Jul 2008, 16:58

Dated1...

I think you might have been wise to read the whole thread, even if it is over 1400 posts, before jumping in with such an ill advised comment.

chris weston

4th Jul 2008, 17:20

Spot on Shaggy Sheep Driver, spot on.

None of it from the book and all in 50 or so seconds gets unequivocal respect from here.

And yes .......I've read every post.

CW

boguing

4th Jul 2008, 18:51

Blimey Chris.

If I'm ever corrected, it's nice to have someone who knows his stuff do it.

I 'knew' that water unfroze at 4C from childhood (ponds/fish/winter).

Thermo section of Naval Architecture degree course did not correct that. Water is wonderful stuff, but not as clever as I thought. Thanks for the lesson.

John

Oluf Husted

4th Jul 2008, 20:25

Dear BOAC,

I stand corrected, TAT it is! (What is the diff. at 250 kts in 10C. weather.?)

"A general lack of crew awareness and training concerning winter operations"

The above sentence was the End result of a study, at Cranfield Institute Of Technology, done by Javid Karim in 1995, over the subject:

"An Investigation Of Aircraft Accidents And Incidents Attributed To Icing, And Cold Weather Operations"

60 airlines participated, among them BA, SAS and Finnair, only the later had sufficient training and knowledge.

Oluf

BOAC

4th Jul 2008, 20:50

I don't think OAT affects it and I also think it is around a 7 degree rise?

ChristiaanJ

4th Jul 2008, 21:27

"I 'knew' that water unfroze at 4C from childhood (ponds/fish/winter)."
What's this fixation with +4°C?
I thought water was this weird stuff that reached max density at +4°C but froze at 0°C?
So, roughly speaking, when air temp went down below zero, the surface would freeze and the 'warmer' water underneath would sink to the bottom.

petermcleland

4th Jul 2008, 21:52

I think that due to something called "Latent Heat", it doesn't actually freeze or unfreeze at 0 degrees C even though the temperature of ice is 0 C. Water needs to go a bit below that temperature to solidify and a bit above that temperature to become liquid again.

Smilin_Ed

4th Jul 2008, 22:17

Well, I didn't really understand Entropy in Thermodynamics 201 so now, 50 years later, I must break out that old text book and go through it, and the Calculus that supports it, again. Maybe I'll get a better handle on it this time. Maybe more of us should do the same. The more brains thinking about it the better. This really is a complex problem which probably does not have a simple answer.

Dated1

5th Jul 2008, 09:53

You are right in that I did 'jump in' before reading the entire thread but I have just put that right by spending the last four hours looking for something regarding airmanship and aerodynamics as apart from the well argued technical aspect of the initial failure of the aircraft.
I began this reply by 'cherry picking' a number of posts that reflect my own thoughts but elected not repeat them as you have undoubtedly read them anyway.
However, to the point. Accepting that the aircraft was effectivly on a dead stick approach...the nose steadily rising as the speed falls...the 'picture' of the world outside starts to look wrong...asi?...108?...ooops...which way do I move the 'stick'....let me think....
Why did the FP, seeing that the AP was maintaining the glideslope at the expence of airspeed, choose not to disconnect the AP?
Stress, fatigue, workload?
All I ask is that the perfomance of the pilots at the time is evaluated.
Is that so very unreasonable?

petermcleland

5th Jul 2008, 11:51

Dated1

I just think that you should accept that many experienced pilots here, including those with much experience on type, have come to the conclusion that the actions of the two pilots in the very limited time that was available to act, performed a series of actions including the odd one outside the book, that resulted in the aircraft arriving on the grass short of the runway, with no fatalities. It is generally considered here that with actions other than those performed, the aircraft would have finished up the wrong side of the fence having demolished a number of obstacles and vehicles with great loss of life.

Most pilots here think that they did a great job :)

Dated1

5th Jul 2008, 13:26

Well...with the greatest respect, and after having read the entire thread this very morning, I feel that 'most pilots' were not so sure that a great job had been achieved from 750' there is more than a 'very limited amount of time' available.
Although the aircraft 'cannot stall' the landing was so hard that an undercarriage leg went up through the wing. Stalled or not that aircraft virtualy fell the last few feet.
Of course, I wasn't there and it is easy to speculate from the lhs of my sofa these days but allow me to offer a sample of my mornings 'cherry picking' and again simply express the hope that the eventual enquiry will publish the results of a pilot perfomance evaluation.

Happy reading...

I would expect that the natural reaction would be to take manual control, knowing that the autopilot would attempt to maintain the glideslope to the detriment of the airspeed. The way I read this report (and I may well have got the wrong end of the stick of course) is that the aircraft must have stalled (read 'descended rapidly') after the autopilot 'flew' the aircraft to 175' and 108kts and disconnected itself.
--
As far as the kudos for the "wonderful" job the Autopilot did...
If I were handflying this approach, and lost thrust, would I sacrifice altitude for airspeed ( to prevent a stall ), damm fckng right I would.
And YES, with a loss of thrust, I KNOW I could FLY it to the ground a WHOLE lot better than the A/P. This is airmanship 101 guys. The only question I have is at what point do I realize I had no thrust and then act.
--
It seems apparant that the A/P remained engaged down to 175 feet. Although the A/P is a pilot`s best friend in most emergency situations, perhaps it was not the case in this instance.

The speed at 750 feet must have been about 140 Kts.
The speed at 200 feet was 108 Kts.

As the the A/P was engaged, the AFDS was trying to maintain the glideslope, with a probable linear speed decay. The speed loss was approximately 32 kts in 500 feet.

Every kt of speed below VRef 30 would result in a worse Lift/Drag ratio, with the result that the aeroplane could not eek out as much distance as it potentially could if it was flying at it`s best L/D ratio speed (approx VRef). At 108 Kts, the L/D ratio would be significantly reduced.
---
The AAIB is explicit in saying that flap 30 was selected. No mention is made of decreasing the flap selection.

The usual jet airliner L/D of 18 is for the clean configuration and I suspect that flap 30 yields substantially less. A simulator run would present the raw F30 L/D, but in any case we did have some thrust and the achieved slope and L/D is derivable from the FDR.

There are a number of flapped gliders that use flaps to add drag. The big caution with flapped gliders is not to add too much flap as you can lose considerable altitude reducing flap. Many glider approach accidents have happened when flap was reduced with insufficient altitude.

I would not want to explore in the air how the 777 with thrust restricted to the accident setting reacts to a flap reduction attempt at 600', but it's possible the AAIB will decide to investigate that in a simulator.

In a high drag situation, increasing airspeed increases drag substantially. With flap 30, the best L/D speed would be lower than with lesser flap selections.

With gliders that have powerful spoilers and/or flaps, you can select full spoilers and/or flaps full on and if you are still not coming down steeply enough, add airspeed to steepen the slope.

In this accident, we see a trade of airspeed for glideslope, mostly at the behest of the autopilot. Given the touchdown point and the 108 kt. cited by the AAIB, they were amazingly lucky.

It was an interesting decision by the crew to leave the autopilot engaged as the speed decayed.Perhaps there was a good reason for this. Perhaps they were understandably so preoccupied with trying to work out why there was no response from the thrust levers, that the speed decay went unnoticed.However, the reason why the autopilot allowed the speed to decay was not because it was attempting to fly at the best speed for the situation presented to the crew. It was because it was attempting to maintain a glideslope that it was commanded to follow. Unfortunately, a decaying speed from about 140 knots at 750 feet to 108 knots at 200 feet, resulted in a severely degraded flight path angle. If the autopilot/authorottle is not performing what it is commanded to do, (in this case maintaining the commanded speed), then it is best to disconnect, and correct the situation manually.In this instance, as the speed started to decay, an autopilot disconnect followed by flying at a speed of between VREF and VREF minus 10 would, quite probably, have resulted in a different outcome, and a more controlled landing.

This is true...to an extent. However, in my company the following is beaten into us with a metaphorical big stick (and rightly so) at every recurrent: Aviate, Navigate, Communicate.

Someone has to be flying the aircraft at all times, either manually or through the automatics. With a loss of thrust at that height, it would not do to have both crew trying to troubleshoot the problem. One of them HAD to be flying the aircraft. With that in mind, personally I find it suprising that the PF would choose, seeing that the AP was trying to maintain the glideslope thereby rising the nose causing the speed to bleed off, to leave the autopilot in to the point that it disconnected itself at 108kts.

lomapaseo

5th Jul 2008, 14:07

Although the aircraft 'cannot stall' the landing was so hard that an undercarriage leg went up through the wing. Stalled or not that aircraft virtualy fell the last few feet

The above is a kind of subjective (eyes of the beholder) support for your argument in my view.

To my knowledge nobody has published the vertical g rates for the landing suggesting that it "fell" out of the sky. The track of the landing gear suggests that it was a lateral force that broke it as designed, from ploughing through the soft earth along the flight path.

Of course there is plenty of room for discussion here (CRM) once the facts are released.:)

BOAC

5th Jul 2008, 14:16

Dated - you are now stirring a dark hornet's nest. You rightly describe 'the lhs of your sofa' and that is where we are both looking at this from. Whether the crew did behave to the best of their ability is not for us to judge. Nor is it really for us to even expect that they would have. Your figures actually indicate that leaving the a/p in with a similar failure at, say 550' would have been a 'perfect' solution. Put yourself now in the cockpit at 750'. Insufficient power. A windscreen full of a busy trunk road with factory buildings before it. It is going to take significant foresight to lower the nose and 'dive' at the road, lorries and cars, plus the buildings and fence, expecting the float and airspeed bleed to carry you over it. At what height do you start the 'flare'? Will the tail clear that high lorry? Unfortunately, a decaying speed from about 140 knots at 750 feet to 108 knots at 200 feet, resulted in a severely degraded flight path angle. - this, of course, is only true of the OVERALL FPA - the ACTUAL, from 750' to 200' was seductively 'normal' at 3 degrees. Think about that.

To decide whether to raise flaps or not, as I have said earlier, is an unknown to me. Yes, leaving the a/p in until it disconnected courted disaster. I do NOT know how I would have reacted and nor, I suspect, do you?

I would query your 'statements of fact' regarding best L/D and I don't actually think Vref has ANYTHING to do with L/D? As for 'eeking out as much distance as it potentially could" - we all know that using the last few knots of airspeed down to just above stall CAN be more beneficial than maintaining best L/D in 'stretching that glide'. The unknown variable is from what height does that work better. Neither of us know for sure.

There will be an analysis of the crew actions, certainly inside BA, and probably some lessons will be learnt. I would not presume to make that analysis. I do not think any benefit can come with these 'ifs and buts' here.

Starbear

5th Jul 2008, 14:34

the landing was so hard that an undercarriage leg went up through the wing. Stalled or not that aircraft virtualy fell the last few feet.er no, it didn't actually. It penetrated the tertiary structure aft of the wing and sizeable pieces of structure poking upwards in the photo are the gear leg and the beam which supports the pivot or trunnion. Look carefully at the intact wing forward of the gear oleo. If I recall there was no fuel leak except a small one from the centre tank?

http://i317.photobucket.com/albums/mm382/bairbus/oleoandgearbeam.jpg

trident-too

5th Jul 2008, 14:39

Having done a"thesis'(of sorts) at Uni. on the physical properties of water,I can confirm that water(pure water that is) is at it's densest at +4degreesC. Hence,during countless ice ages of the earth,this layer of warmer water under the ice allowed micro-organisms th survive.What this has to do with this thread ,I've no idea!!

Shaggy Sheep Driver

5th Jul 2008, 15:24

Flaps increase lift and drag, and of course the flaps on the 777 and other airliners also increase the wing area. But the later stages of flap are almost all drag-producing, and provide little if any lift. I don't know the 777, but I wouldn't be surprised if the flap setting normally used on a powered approach would be far too draggy if the power fails and there is a sudden need to stretch the glide.

Reducing flap to get rid of the drag, but not reducing it to a point that significant lift starts to be lost as well, will not result in any sink and will be benficial to an aeroplane in the situation that 777 found itself in.

SSD

Smilin_Ed

5th Jul 2008, 15:35

Dated1, you're beating a dead horse. :ugh: The crew did a commendable job. The task now is to find out why the engines didn't respond to a requested increase in thrust. Nothing more.

arcniz

5th Jul 2008, 23:57

While I am not the world's greatest typist, the time it has taken to type THIS sentence is approximately the time available for the entire process on BA038, from recognition of problem to arrival.

And that's without the time for some minor corrections after the fact - an opportunity the flight crew did not have.

They took and passed with honours one of the shorter courses in test piloting in the whole history of aviation.

It seems a very satisfactory result, all considered. Job well done.

Milt

6th Jul 2008, 00:26

Smilen Ed

No doubt the crew did a commendable job under the circumstances.
I don't think many of us could claim to have been able to do much better.

What we are doing here now is attempting to suss out the optimum actions that would have 'stretched' the inadequately powered glide and perhaps have resulted in the gear reaching the hard stuff.

This is a continuing process for the skilful operators who seek to learn from opportunities such as this particular set of complex circumstances. I guess you can call it learning the hard way!

point8six

6th Jul 2008, 07:42

Any evaluation of the crews performance will be contained in the AAIB's concluding report. It will be up to the various regulating authorities to make recommendations, regarding operating procedures for the B777, as necessary.
My own thoughts at the moment, are that pushing the nose down to increase speed, might have led to a large hole in the ground to the east of the A30! -but at least the a/c would have hit the ground at the right speed:rolleyes:. Perhaps Right1 can share his/her knowledge of the B777's ground effect? Stretching the glide was quite obviously a successful manoeuvre, since all on board lived to tell the tale.:D

Bis47

6th Jul 2008, 07:51

While configured with "landing Flaps", and flying at Vref, you have 30% margin against the stall (or minimum flyable airspeed, wahatever the terminology). Il, at that time, you retract flaps to "approach flaps setting", you are left with at least 20% margin above the stall ... and much les drag.

Retracting the flaps to the "aproach flaps setting" is one of those required immediate actions if you start a go-around initialy in "landing flaps config" and get an engine failure at the same time.

Any-one with a good training is familiar with this flaps retraction, so I can understand that the crew might have reduced the flaps from 30 to 25 without taking a chance of immediate stall.

Now, when I read that so many members consider that letting the auto-pilot fly the aircraft in such a situation -and loosing more than 30 knots in the process - is "doing a good job" ... I wonder about their degree of basic piloting skill and about their airmanship ... if any.

It was stated somewhere that replaying the situation in the simulator with more "creativity" resulted in an almost normal touchdown at the very beginning of the tarmac. No wonder ...

Analysis the crew performance will indeed give usefull information about the effectiveness of their previous training (flying skill, airmanship, crew co-operation), and as a matter of consequence, of modern, minimum training in general. "System operation" training ...

Dream Buster

6th Jul 2008, 08:08

Dated 1,

We obedientally take it that the AAIB always leave 'no stone unturned' in their quest to provide ALL of the factors in any serious accident; especially unsolved accidents after many months of digging for clues?

I wrote to them a few months ago asking if the AAIB had checked the pilots blood and fat either at the time or subsequently. I then wrote again about another serious accident at EMA / BHX, with much the same reply.

Apparently as 'It is not the AAIB's policy to routinely subject a surviving crew member to blood/fat tests unless of course, the individual themselves complains of feeling unwell at the time of the occurence'.

***CRASH!*** AAIB "How do you feel?" Surviving pilots "Oh great, thanks!"

Anybody who has experienced the cumulative / acute effects of contaminated air will know the disastrous results it can have on ones performance. Indeed, the AAIB have helpfully published the effects in pilots own words over the years in many other incident reports. The majority obviously go unreported. Here are some 'officially published' descriptive words.

Difficulty concentrating, feeling of fainting, odd pressure in the head, nasal itching and ear pain, felt discomfort and a feeling of ‘moon walking’, mild dizziness, very nauseous, markedly dizzy and groggy, difficulty focussing, light headed and hot, felt progressively worse, tingling feeling in fingertips and arms started shaking, “feeling dreadful”, white face and pupils dilated, hands trembling, double vision, light headed and tired, dazed, headache and eye irritation, blisters inside mouth, tight chest, sore throat for days, coughing, metallic taste in mouth, tingling sensation on lips, errors of judgement and garbled speech, verge of passing out, tunnel vision, loss of balance, loss of feeling in hands and lower arms.

Perhaps by coincidence, chemicals are also found in ones blood and fat - just like an athlete may be hauled over the coals for having specks of performance enhancing drugs in their bodies or drunk drivers are grounded for their known performance degrading effect. Even many affected pilots memories have also been professionally measured as being 'abnormal'.....

Dated 1, i'm with you. Some very non SOP things happened on both those days at LHR and EMA/BHX in extraordinary circumstances and I wouldn't bet that leaving the auto pilot in until the last second in BA 038 was not actual skill - but more like pure luck.

Good for them, all those pilots did a great job in the circumstances. But what were those circumstances. Exactly?

Who thinks that pilots should routinely have their blood / fat tested after such an incident? If only to rule out any question of pilot's being influenced by anything.

It STILL doesn't add up.

If you are one of the 70% who have never been affected by contaminated air then lucky you; but please have the courtesy of listening to the apparent minority who have experienced the devastating above effects whilst operating a public transport aircraft, often totally unaware of the likely reason.

It can all be very confusing but requires understanding - urgently.

DB :ugh:

BOAC

6th Jul 2008, 08:16

"so many members consider .......doing a good job" - I think you are mis-reading most of the 'pilot' posts? The overall impresion we have is that the END result was a 'good job' ie no-one died. Most of us are happy to await the outcome of the various enquiries. Whether the actions were 'the best' is relevant but not 'big picture' stuff.

The post before yours by point8six certainly reflect my views, and, I'm sure, many others.

spinnaker

6th Jul 2008, 09:15

Who thinks that pilots should routinely have their blood / fat tested after such an incident? If only to rule out any question of pilot's being influenced by anything.

Well, if we take it that the pilots are part of the flight system, and all other parts of the system are examined, then why not medically examine the pilots. They may be the system component that has broken.

Flight Safety

6th Jul 2008, 14:01

Dated1, you're not thinkng clearly. Consider this:

At 700ft, landing gear and flaps out, you suddently discover engines don't have the power to maintain glide slope, you quickly know you're going down. Point the nose, try to stretch the glide to the runway, retract the flaps a notch to lower drag (but only a notch, because you don't have the airspeed). Quickly you realize you don't have the energy to make the runway, and this is ALL about energy.

You then see you can make the infield grass, but how fast do you want to set down on it, 140kts to 150kts? The undercarriage will be ripped off anyway in the soft grass and soil, so point the nose in the air near the stall, and touchdown at 108kts instead. Sure it'll be a hard touchdown and the undercarriage will be crushed and ripped off (was going to happen anyway), but you won't slide very far with much less energy to disintegrate the airframe structure. Also think of the undercarriage as a beneath the airframe crumple zone.

As I said this is ALL about energy, especially when contacting unpredictable terra firma instead of a hard straight runway. Keep the energy levels down on impact, and everyone lives.

All in all, this was outstanding airmanship, the results speak for themselves.

TeachMe

6th Jul 2008, 14:09

OK, Dangerous to post on this thread in relation to the pilots, however one point I have not seen mentioned before is below.

First however I would like to, for the purpose of this post, to take it as given that in this situation these pilots made at least good decisions for this situation. Further, those decisions resulted in no major injuries and would not have been bettered by perhaps 99% of other pilots in similar circumstances. As such there is thus no room to personally criticize these pilots. Whether you agree or not with this is immaterial to this argument as it is taken as given.

Now, lets imagine this fuel/engine issue had occurred just a few seconds (2-3??) later. In such a situation, it could be argued that the pilots would have made exactly the same decisions, but the result could then have been a scrape on the runway, fire, and perhaps many deaths.

Alternately it could have happened a few seconds earlier and only that 1% of better pilots would have been able to even land it even on the grass.

Would it be fair to criticize these pilots in either of the other two situations? I would suggest not, even though they may have resulted in many deaths. The simple fact is that the lack of injuries seems to be a result of pilots making reasonable decisions in a window in which those reasonable decisions were able to have a mostly positive outcome.

Going back to the question about pilots posted above, I do think it is reasonable to question the pilots actions, but ONLY from the perspective of seeing if it would be possible to somehow increase the chance in the future that the right decisions are made within the right window. In reality, I don't think this is possible, but asking if it is possible does seem important.

TME

Dated1

6th Jul 2008, 15:05

Let me refer back to my original post, 1464, and perhaps make it clearer that no critisism of the pilots is intended. I just wish to see a clear pilot evaluation carried out for the further education of those still fortunate enough to be on a flight deck. Milt, post 1486, got the point of my thinking as did Bis47, post 1488, along with several others. Point8six, post 1487, 'Right1'? Loved the humour. A valuable contribution to this thread.
Rightly or wrongly, and please forgive this, I have always felt that a pilot is better for substantial glider experience, preferably current and on flapped gliders. I warmed to any young man, or young lady, in the rhs that mentioned gliding, but perhaps word had got out...
Such pilots are high on 'stick and rudder' flying. Would my gliding experience have kicked in and reverted to 'flying', put the nose down and trade altitude for speed in a 777? No idea. In a 737? Absolutely.
Thank you however for all of your comments gentlemen. How wonderful this site is for communication with you. Any tips for how to get my old airframe and this sofa airborne would be so welcome.

BOAC

6th Jul 2008, 15:21

Any tips for how to get my old airframe and this sofa airborne would be so welcome. - helium ballons and an air rifle?

If you trawl back into the long grass on this thread you will see unequivocal 'statements' (as yet unsubstantiated) by BA pilots that the flap WAS changed and that sim evaluation runs have shown this was beneficial by several vertical feet.

There is an ace gliding BA man, who when I last heard was in 777's RHS. As an ex 'glider' I know what you mean.

John Farley

6th Jul 2008, 20:37

Three points I would like to throw into the chat –

The inertia of a large aircraft acts in the pilots favour when stretching a glide (the opposite is also true if you stuff the nose down in an attempt to trade height for speed).

Modern swept wing airliners will have a lower lift curve slope than a modern glider and so can be expected to have a more progressive, gradual and benign stall.

While there are several reasons why airliners are certificated to fly the approach at 1.3 times the stall speed it does mean that there is a bit of slack when it comes to stretching the glide.

Smilin_Ed

6th Jul 2008, 22:06

M.Mouse

6th Jul 2008, 22:17

No they don't, at least not on any Boeing production aircraft which I have ever flown.

The question would have to be asked how useful it would be given that the instances of jet transport aeroplanes gliding are mercifully rare!

Re-Heat

7th Jul 2008, 09:34

Do large jet transports like the 777 have an angle of attack (AOA) indicator? If so, there should be a published AOA for the best glide speed for each flap setting. AOA takes the guess work out of it.
It is an option on the 777, but I do not know how many operators display the information. Regardless, the AoA gauge information is translated into various other more suitable readouts, and we are not dealing with a FJ operating at AoA limits in normal flight.

point8six

7th Jul 2008, 14:17

Dated1 - at least you still have a sense of humour in your old age!
I think John Farley - as ever - has a very valid point when considering the inertia of large aircraft. I have not flown the 737, but have flown a British jet with a similar wingspan, however, it had all the gliding properties of a 'brick-built out-house' especially in ground effect (it was unaffectionately known as The Ground-Gripper). I still think that instinctively most pilots (non-gliders) would trade speed for height to make the threshold.
As for getting your old frame and sofa airborne - why not follow your own advice - lower the nose, build up airspeed and wait for the ground effect - ouch!:ooh:

Smilin_Ed

7th Jul 2008, 20:58

M. Mouse wrote: "The question would have to be asked how useful it would be given that the instances of jet transport aeroplanes gliding are mercifully rare!"

I too hope that using AOA to stretch a glide would not happen often, but it would also be useful for ordinary landings because it automatically provides the proper speed for the actual weight of the aircraft without any calculations, especially if your calculations (or fuel quantity readings) are wrong.

Re-Heat

8th Jul 2008, 08:57

Goodness knows how I recall this, but I read this article a number of years ago regarding AoA readout installation in Boeing Aero:

So, if the approaches were flown on a daily basis by reference to a fixed-approach AOA based on a margin above stall, at any CG aft of the forward limit, the probability of tail strike would be greater than the current practice of using approach airspeeds.

Full article: Aero 12 - Angle of Attack (http://www.boeing.com/commercial/aeromagazine/aero_12/attack_story.html)

NigelOnDraft

8th Jul 2008, 10:17

but it would also be useful for ordinary landings because it automatically provides the proper speed for the actual weight of the aircraft without any calculationsAirbus effectively does this, since the PFD "characteristic speeds" are Alpha derived, and hence if weights are wrong, the PFD and FMGC speeds disagree ;) I would imagine B777 type technology has something similar...

NoD

GearDown&Locked

8th Jul 2008, 10:50

I think the cavitation found in the pumps is probably misleading the line of thought of everyone in this forum. IMHO cavitation could have happened prior to the event in question, like a couple of days (or the sector) before. So leaving the cavitation signs aside:

If the fuel metering device was giving a “false” reading, somewhat bellow true fuel flow, when the A/T commanded an increase of thrust it would have increased initially to the requested value but then the excess of fuel in the burners would made it drop dramatically but not entirely. Thrust decays, FADEC opens fuel valves even further to compensate, but instead of correcting it worsens the problem.

Too far off the mark?

GD&L

Green-dot

8th Jul 2008, 11:17

If the fuel metering device was giving a “false” reading, somewhat bellow true fuel flow, when the A/T commanded an increase of thrust it would have increased initially to the requested value but then the excess of fuel in the burners would made it drop dramatically but not entirely. Thrust decays, FADEC opens fuel valves even further to compensate, but instead of correcting it worsens the problem.

Too far off the mark?

Or was the excess of fuel in the burners in this scenario a mix of fuel, ice and water?

Thawing Ice, perhaps shedding from the compressor stages as the engines revved up from approach idle to a new target thrust setting, quenching or partially blocking the annular combustion chambers on both engines? In this case the anticipated EGT increase with reduced gas flow may have been negligible due to the cooling effect of water, hence no RPM increase but instead (partial) rollback to somewhere above idle?

Green-dot

snowfalcon2

8th Jul 2008, 15:47

I'm fairly convinced the subject of a possible "stretching the glide" will be included in the accident report. As I see it, the report may suggest one of three things:
a) do nothing;
b) recommend additional flight crew training for handling low-level double engine failure;
c) recommend improved autopilot designs that automatically trim the plane for optimum glide range when sensing a power loss situation.

Each of the alternatives need to be judged on basis of the resulting increase in safety compared to the probability of this type of engine failure, as well as the implementation costs. Also we have to await the outcome of the search for the primary engine failure reason. In case that is not found, the case for doing something (b or c) becomes stronger.

ChristiaanJ

8th Jul 2008, 16:13

Unless autopilot design has fundamentally changed since my days, the (pitch) autopilot would have no way to 'sense' an uncommanded power loss.
It did its job, i.e., keeping the aircraft on the 3 degree glideslope by increasing pitch (and thus AoA) until things got too hairy and it disconnected.
It 'expected' the autothrotlle to keep the speed up.

CJ

snowfalcon2

8th Jul 2008, 16:29

that's exactly my point, with today's computer technology it would be no big deal to design a capable integrated autopilot/autothrottle. It's about time, too, considering the technology advances in most airplane systems.

Joetom

8th Jul 2008, 19:33

Talking about inputs that an A/P system may get in the future, I can think of two off the top of my head.

1. Fuel Temp.

2. Amout of Water in the Fuel.

Smilin_Ed

8th Jul 2008, 20:26

Reheat, thanks for a very good article. The most important part is: "AOA information is most important when approaching stall." The U.S. Navy has used it to very good advantage for about 50 years now in making carrier approaches.

ChristiaanJ

8th Jul 2008, 20:37

Joetom,
Again confusing A/P and A/T.

Phil1980's

10th Jul 2008, 16:18

Have a read of this...noone seems to be thinking of googling past events
200204444 (http://www.atsb.gov.au/publications/investigation_reports/2002/AAIR/aair200204444.aspx)

Golden Rivit

11th Jul 2008, 22:23

Dont know if this has been seen before, http://www.iasa.com.au/folders/Safety_Issues/others/speculative.html

PAXboy

11th Jul 2008, 22:43

snowfalcon2with today's computer technology it would be no big deal to design a capable integrated autopilot/autothrottle. It's about time, too, considering the technology advances in most airplane systems.
Non pilot speaking
My guess as to why these things might take longer to get more closely integrated - is the certification process. How long would it take to get approval of a new set of controls, software, interlocks and all the rest? The manufacturers will work on the basis that it ain't broke and if the customer ain't demanding it ...?

NotPilotAtALL

11th Jul 2008, 23:00

Hi,

http://www.iasa.com.au/folders/Safety_Issues/others/speculative.html

Thank you.
This was published on the IASA site the 01 Feb 08 and rely to a official report.
Wonder if no more official news was released from this date.

Cheers.

misd-agin

12th Jul 2008, 01:53

You shouldn't need an AOA gauge to understand that at a slow speed reducing speed increases your AOA, which will decrease your gliding distance.

Decreasing speed from 1.3 Vso to close to stick shaker speed will not stretch the glide at altitude. It does in the end game, and allows some airspeed to 'flare' as opposed to hitting the ground at whatever sink rate you have at, or close to, stickshaker.

Reducing flaps from 25/30(Landing slat configuration - full) to 20 (Takeoff slat configuration - mid) might be critical to improving your gliding distance.

Obviously the lowest drag configuration is best, but sometimes the gain achieved via decreased drag doesn't make up for the increased sink rate generated by the need to increase flying speed to your new, and faster, approach speed. Early? Yes. Late? No. Beats me what the actual difference between 'early' vs. 'late' is. That's the gut check time.

thinkingpilot

13th Jul 2008, 20:06

may i ask anyone who knows how long its going to be before the aaib comes out with a FINAL report . they have had 6 months, all the facts , the airplane itself ,and the crew at their disposal. speaking as a 777 driver myself we fly everyday wondering what happened . delay in releasing reports in my experience, i am sorry to say,. sometimes indicates cover up. excuse my poor typin skills

atakacs

13th Jul 2008, 20:33

@thinkingpilot

Our best guess is "as soon as they have something"... As far as one can tell they are at loss for an explanation.

And I'm pretty sure "we don't know" won't be good enough for you, especially if you really are a 777 driver :O

snowfalcon2

13th Jul 2008, 21:35

My guess as to why these things might take longer to get more closely integrated - is the certification process. How long would it take to get approval of a new set of controls, software, interlocks and all the rest? The manufacturers will work on the basis that it ain't broke and if the customer ain't demanding it ...?

Yes, basically the requirement has to be included in the aircraft certification standards in order to get things to happen. And for that to happen there usually needs to be evidence of a number of accidents that could have been avoided.

Now in this case I don't immediately remember any other case of a low-level double engine power loss of this "sneaky" type, on approach with autopilot engaged. Those that come to my mind have happened on take-off (SAS 751, MD-82 ice ingestion, and the recent Citation at Farnborough, Kent) which is an altogether different situation. However, the proposed integrated autopilot/autothrottle might also have helped in the "Gimli Glider" case (which occurred at cruise altitude), had the captain not happened to be an experienced sailplane pilot.

Anyway the key issue, as I see it, is whether this type of fault has a high enough probability to justify new safety measures and their associated costs. The investigation will hopefully shed more light on this.

arcniz

14th Jul 2008, 02:01

Yes, basically the requirement has to be included in the aircraft certification standards in order to get things to happen. And for that to happen there usually needs to be evidence of a number of accidents that could have been avoided.

Fundamental changes of method also go through a cost-benefit filter and a "testability" filter.

Given at least a few incidents of unpowered flight, approaches, and landing sequences in heavy jets, it would seem the cost-benefit (with reference to passenger safety, in particular) argument could be made.

As regards testability, however, the questions are harder to answer. The low, slow, zero-power flight envelope is about as dangerous as it gets for flying a large, heavy aircraft. One can do testing at higher altitudes, of course, but realistic "ground effect" and flare phenomena combined might either require some live tests of each type or a major research effort to create a data-set that could be used for simulation of all reasonable types. The potential variables are so many (for a 'general-case' solution) and the cost of error so high, it would take some considerable courage for an airframe manufacturer to add this function set and pronounce it usable. Would be pretty much a lifetime career for some bunch of lawyers to litigate about that forever after.

Even with all the computers, maybe seasoned pilots and 'seat-of pants' flying still are occasionally the best choice, after all?

.