Swedish Steve,

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

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

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

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

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

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

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

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

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

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


Green-dot

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

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

Accretion.
 

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

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

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

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

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

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

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

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

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

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

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

So, how much ice would it take - do ya think?
 

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

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

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

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

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

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

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

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


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

We'll have to wait and see.

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

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

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

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

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

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

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

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

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

Abolute B****ks :ugh:

NoD

My thoughts exactly !

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

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

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

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

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

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

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

Quote:

---

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

---

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

Brainstorming for a minute - only half-facetiously:

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

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

:cool:

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

Rationalize it as you will mate.

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

barit1 said
It would have to be a fuel storable as a liquid to get the package down to a reasonable size - maybe propane - and it would still require a large, heavy, high pressure bottle. Why does that remind me of the Qantas B744 depressurisation??

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

Accretion vs. Break-off Scenarios
 

I think pax2908 has it right here. Following up on this would also prove, or disprove, snanceki's embracing of the accretion vs. break-off scenario. I agree with snanceki.

Fuel piping dimensions?
 

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

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

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

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

I am just curious.

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

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

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

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

3333333333333333333333

SLF choice of aircraft...
 

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

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

Kind regards ,John

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

md80fanatic 1836

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

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

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

http://en.wikipedia.org/wiki/Fuel_Sy...cing_Inhibitor

Hope this helps.

CW

Puzzling .....
 

Green-dot, Swedish Steve:

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

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

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

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

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

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

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

1. Possible interim safety measures suggested by Boeing

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

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

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

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

see http://www.bloomberg.com/apps/news?p...HA6Kw&refer=uk (although seems to be mistaken reference to "frozen kerosene").


2. Earlier FAA leaked memo

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

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

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


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

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

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


4. Icing scenarios

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

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

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

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

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

Aircraft types
 

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

Rainboe:

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

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

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

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

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

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

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

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


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

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

What utter rubbish. Have you visited flyertalk, and perhaps seen that regular business travellers there have absolutely no qualms about stepping onto a 777 (and they do indeed know what aircraft they are boarding).

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

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

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

These warnings are not visible to the crew, but are stored in EICAS memory.

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

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

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

1. Operational environment

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

2. Design

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


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

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

Just a thought.