Here was me thinking the Telegraph was a respectable newspaper :yuk:

Reading the report, specially this part:
they owe a lot to keeping the autopilot on (and its design as well)!
That way all possible energy was used up to its full extend, bringing the aircraft within the airport perimeter.
I don't think a human could have done it better, probably not, as a pilot would have unconsciously lowered the nose.

Cavitation
 

Can someone explain how 'evidence of Cavitation' in the HP fuel pumps is being considered here?

Is it that the pump is trying to pump from an obstructed source causing bubbles (cavities) in the fuel or that there is evidence that the pumps are physically damaged?

What will be the evidence of cavitation? assuming THIS is a good explanation of such?

:confused:

As observed in an earlier post, all aboard were unbelievably lucky that BA038 ran out of lift where it did, landing on the only bit of waterlogged lawn within miles of their approach path.
I am sure that the 2 pros flying that sector were trying to get it onto 27L, which in the circumstances would have likely had a much more injurious outcome.

http://edition.cnn.com/2008/WORLD/eu...ef=mpstoryview


What was it then if not mechanical?

Evidence of cavitations would be small pits on the tips of the impeller blades of a certifugal pump, and in other key places of the pump (depending entirely on the design).

The pits are caused by the rapid collapse of bubbles.

Bubbles can be caused not only entrained air (such as a seal leak) but also when the fuel vapourises (ie. 'boils') at partial vacuums.

The report does not say that cavitation caused the problems, nor does it say when it occurred, It could have occurred at any time from new, up to the time of the crash.

Cavitation in itself does not cause a problem unless there is failure of the components themselves as a result of it, or unless the effects of cavittion causes a significant degradation of performance.

Cavitation however is a symptom of a choking of flow on the inlet of a pump, or the entrainment of air.

An example of cavitation could be the addition of a lighter solvent in the fuel which vaporises at a lower temperature than the bulk of the fuel. The suction pressure of the pump could cause the vaporisation of the additive and so cause vapourisation. The report does not report fuel contamination so this can be ruled out.

Another example of cavitation is when a restriction which is on the discharge side of the pump is suddenly taken away - the suction flow just cannot keep up, the pressure drops and cavitation occurs.

At this point I still go for: failed seals due to low temperature, then regaining flexibility on loss of altitude, then entraining air and causing foaming.

Cavitation..????
 

Mind the following information given in the report:

I sense Trolls in here.

I don't care whether the autopilot was left in deliberately or not, - it worked.

I do however know far too many professional pilots who believe they can do better than the automatics, usually wrongly!

I wasn't really getting at fuel waxing/freezing in my previous post......I was more thinking along the lines of water Hygroscopicly suspended in the fuel freezing somewhere in the system during the flight.

However all this is pure speculation at this stage.

At least all that garbage . . . . .
 

QUOTE: "BoeingMEL wrote: "............ at least all that garbage about EMI can be buried..... as can fuel exhaustion, windshear, finger trouble, Gordon Brown's heavies..."

To be fair, the report doesn't appear to rule any of that out...

Until the investigation is concluded anything is a possibility!" UNQUOTE

Exactly. Nothing can be ruled out at this time. Reading the report the investigators apparently are confronted with evidence of a normal functioning machine, which for a short period of time did not function normally. In other words, perhaps an intermittent failure of some kind, at this time not yet duplicated.

To quote the report: "The recorded data indicates that there were no anomalies in the major aircraft systems."

Question is then, what could have failed that is not recorded?

Regards,
Green-dot

i smell trouble ahead and no one rightly is going to stick their neck out and rightly till the final report is issued.:ouch:

No Fault Found.

Hmmmm.

The cavitation damage and some FOD in the tanks is not much to go on!!

So there was fuel in the tanks, the metering valve was fully open, and the pump was capable of supplying fuel.

:confused::confused::confused:

This would seem to suggest that the correct signals were getting through to both engines and the engines were trying to respond accordingly. Apparently no other as yet significant defects have been found.

Does this therefore narrow down the possible cause to a momentary absence of liquid Jet A1 under pressure at the burners?

I am totally speculating here, but given that air temperatures were lower than Jet A1 freeze temperature, and even though the tank temperature never got to critical levels according to instrumentation, would it be possible for a deposit (perhaps like cardiac plaque in arteries) of wax or frozen fuel to form somewhere in the fuel pipework?

As it warmed such a plaque could let go, blocking a filter and perhaps giving an engine the mechanical equivalent of a heart attack?

Of course that idea stretches credibility because it had to happen to both engines within seven seconds of each other, there was no EICAS message about clogged filters and it may be physically impossible to put a skin of frozen wax on the inside of a pipe thats carrying -34C jet A1.

No more speculation from me till the next official report.

Re: The Fire Swith does close the Spar Valve!
 

Perhaps worth noting that this was only the case on one wing, on the other side (as I read the report) both paths to the valve were cut by the damage, so no action would have closed it.

Sorry if this sounds oversimplified, but if the tanks had enough fuel, the EECs responded correctly to the request for more power, the fuel metering valves were wide open, and the HP fuel pumps were probably cavitating, then it seems reasonably clear to me that something was probably blocking the fuel flow.

Common mode failure.

Several people have said that the A/P did the best possible job under the circumstances. I'm sure the crew did what any good crew would have done in that situation, but.....

If they had disconnected the A/P when the engines failed to respond to the manual throttle movement and flown the aircraft towards the grass, I bet they would have had enough energy for a decent flare. The landing gear might not have liked coming down in the bog, but I'd take that over a no-flare, near the stall plonk-down. Might have saved some poor sod a broken leg.

Of course you don't expect your jet to turn into a glider on short final and it is easy to speculate with the benefit of hindsight. I'm sure somebody will try it in the simulator, let us know how you get on.

Flame on.

Bearcat wrote

Does anyone know the answer to this question?

What about the cross feed opening and the APU start initiated while the glider was flown by the AP ? What kind of SOP is that ?

Well it is not. It is evidence of the crew trying anything to keep flying. They were not exactly in a "SOP" situation. More out of teh box desperate try anything situation.

X-feed and APU..
 

I imagine that these actions were initiated by the pilot in the middle (relief pilot or whatever he is called in BA).
Maybe not SOP - but sensible actions in a very stressful and confusing situation!:ok:

Two odd things stand out in the report regarding the fuel.

And...

Is it normal for Jet A-1 to have a freezing temp of -57C? Is this really pure Jet A-1, or is it mixed with something else?

I somewhat agree. Not only that, if they had put it onto manual, decreased demand on the engines then the blockage/inleakage/cavitation would have subsided then full thrust may have been regained.

However, I don't feel that we can suggest that the chaps on board did anything wrong. There were no fatalities, no serious injuries, and they landed in a distance shorter than I land a Piper Cherokee into.

T.

A good question - any "lights" in the fuel to reduce the melting point would indeed result in a higher liklihood of caviation in the pumps, or could result in waxes in fuel lines to being stripped then passed through once the right temperature (read 'altitude') is reached.

T.

PS Is it normal for fuel not to be tested for water after fuelling?

X-feed and APU
 

I'm talking about these statements from the preliminary report:


• The fuel crossfeed valves were closed in flight according to the flight crew, but the switches were found in the open position and only one valve was open. In the days following the event, the flight crew has added additional details to their report. The crew now believes they opened the valves just prior to impact and the airplane lost power before both valves moved to the open position.
• The auxiliary power unit (APU) began its auto start sequence, even though the buses were still powered. In the days following the event, the flight crew has added additional details to their report. The crew now believes they turned the APU on prior to impact. There was sufficient time before the impact for the APU inlet door to open, but not for the APU fuel pump to turn on or the APU engine to start spooling up.

Is the crew supposed to retract the added comments they made about it ?

UUUUUUUUUUMMMMMMMMMMHHHHHHH???????????Air in the fuel pumps where normally fuel should be???? Me thinks this is starting to go in a certain direction!!!!!!!11:hmm:

flugmann
 

I read so much rubbish here on pprune and the 777 acident is typical of the misinformed judgemental crap which somehow seems to dominate !! It's a good idea to have these forums but who aside from the newspapers benefits ? hey ho !![

sispanys ria

I think the 'report' you quoted actually appeared on a US aviation site, and purported to be a leak from the official investigation. The initial report, and the update report on Jan 23rd, didn't mention the pilots' 'recollections'.

So I think we can discount the leak?

Yes, it is normal. The fuel gets sample tested during the refuel, and for various reasons it is highly unlikely that water can get on to the aircraft at this point. The AAIB reports states that there was not an unusual amount of water in the fuel recovered from the aircraft, so water does not look like a likely culprit.

Also the schedule for water drains and the likely freezing temperature of the fuel was previously explained/predicted by other posters on the forum, so nothing unusual or unexpected there. Even the FOD in the tanks doesn't really explain much. Still a big bloody mystery.

Water Drain Checks
 

Yes.

The fuel at the bowser will be checked by the refueller before and after refuelling.

The fuel in the tanks will only be checked as required by the maint schedule. (Daily Check, First flight of the day, 'x' hours on the ground etc).:ok:

In light of the first reports, I took the last report to indicate that, prior to the event (during the normal part of flight down to 700'), the crossfeeds were not activated.
As previously discussed, the 777 SOP for low fuel is to open one crossfeed. The Captain may have suspected low fuel. And two sources are better than one (electrically, too, it seems... cf spar valve comments in the report).

Re the comments about seals....
The fuel is being pumped from the tanks under pressure (by wing tank pumps). Any leaks in seals are going to put fuel to atmosphere, not air to fuel lines. The wing pumps were working normally.

Re the comments about foreign objects being in the tanks being put there by maintenance...
Not diverting attention away from maintenance, but how big are the filters (if there are any) on the refuel bowsers?
Also, I've never been inside the tanks of a 777... Just wondering how big the screens are on the pump inlets (frying pan size?).

I'd love to know what caused this...I've been having similar problems with my car for weeks... and can't figure out whether it's the ECU or fuel flow (coincidentally, I found a plastic foreign object under the pump inlet.... the problem still there after removing it, however) :}

Re the references to JetA1 in the report....

Would this be because the fuel loaded in Heathrow was Jet A1 and flight crews are told, where there are combinations of fuel types in tanks, to enter the freeze temperature of the fuel type with the highest freeze point into the FMC/CDU?

If they entered -47, then the aircraft would have warned them at -44 (3 degree buffer)....well above the freeze point of the remaining fuel.

I notice the word satisfactorily is used in several places in the report. What margin of error does "satis" allow? :}

Not sure I follow you there. If there's a blockage upstream of the HP pump the pressure in the line feeding into it is going to go from positive to negative pretty quickly (the pumps cavitated for some reason - not enough pressure being delivered to them is a reasonable inference).

Given that the lowest recorded fuel temperature was -34 degrees, it's a moot point.

I don't think you can enter the fuel temp in that way. I believe the Boeings are hard wired to warn you at -37C.

Four pages of speculation based on an interim report of a basically intact a/c has produced suggested
1. Fuel contamination - culpable
2. FOD blockage of tank outlet - culpable
3. Loss of sealant plasticity due to abnormal low temp (as per Challenger O rings?) which may allow air to be sucked into the fuel flow - not predicted
May explain fuel leak on landing but more likely due to heavy landing
4. Cavitation damage to fuel pump insufficient to impair pump performance, suggesting recent damage - symptom not cause
5. Loss of thrust from both engines at ~200' -SOD's law

Would not partial blockage at tank outlets cause low pressure downstream causing a dose of the 'bends' in the fuel system or draw air in via any sealant crack, thus causing cavitation?

It appears that all pilots, both human & auto, remained fully functional

I await the final report with interest