Ice in fuel caused Heathrow 777 crash
Nasty chill provoked reduced fuel flow
The Air Accidents Investigation Branch (AAIB) has concluded that the 17 January crash-landing of a Boeing 777 at Heathrow was probably caused by "ice within the fuel feed system" which restricted flow to the engines.
BA038 (G-YMMM), after a routine flight from Beijing, suffered reduced thrust in both engines while coming into land and fell short of the runway. The AAIB explained earlier this year:
The first officer took control for the landing at a height of approximately 780 ft, in accordance with the briefed procedure, and shortly afterwards the autothrottles commanded an increase in thrust from both engines. The engines initially responded but, at a height of about 720 ft, the thrust of the right engine reduced. Some seven seconds later, the thrust reduced on the left engine to a similar level. The engines did not shut down and both engines continued to produce thrust at an engine speed above flight idle, but less than the commanded thrust. The engines failed to respond to further demands for increased thrust from the autothrottles, and subsequent movement of the thrust levers fully forward by the flight crew.
Following examination of the aircraft, the AAIB was able to report: "The high pressure (HP) fuel pumps from both engines have unusual and fresh cavitation damage to the outlet ports consistent with operation at low inlet pressure.
"The evidence to date indicates that both engines had low fuel pressure at the inlet to the HP pump. Restrictions in the fuel system between the aircraft fuel tanks and each of the engine HP pumps, resulting in reduced fuel flows, is suspected."
Quite what caused this restricted flow proved a bit of a poser, but the AAIB now confirms (pdf):
The investigation has shown that the fuel flow to both engines was restricted; most probably due to ice within the fuel feed system. The ice is likely to have formed from water that occurred naturally in the fuel whilst the aircraft operated for a long period, with low fuel flows, in an unusually cold environment*; although, G-YMMM was operated within the certified operational envelope at all times.
The AAIB, while describing the incident as "the first known occurrence of this nature in any large modern transport aircraft", stresses: "All aviation fuel contains water which cannot be completely removed, either by sumping or other means. Therefore, if the fuel temperature drops below the freezing point of the water, it will form ice. The majority of flights have bulk fuel temperatures below the freezing."
Among its recommendations attached to the latest report, the AAIB urges "that the Federal Aviation Administration and the European Aviation Safety Agency, in conjunction with Boeing and Rolls-Royce, introduce interim measures for the Boeing 777, powered by Trent 800 engines, to reduce the risk of ice formed from water in aviation turbine fuel causing a restriction in the fuel feed system". ®
Bootnote
*During its investigation, the AAIB noted that during flight BA038 "there was a region of particularly cold air, with ambient temperatures as low as -76°C, in the area between the Urals and Eastern Scandinavia".
COMMENTS
Complete arse.
'Probably' cause it, in other words WE HAVE NO IDEA WHAT HAPPENED BUT FROM OUR INVESTIGATION OF THE TINY PIECES OF DEBRI WE FOUND WE CONCLUDE THAT ICE MUST HAVE BEEN THE CAUSE.
I hate air accident investigators, they're just educated guessers.
So @steve
So steve Boeing learnt a lot by closing the hearings and restricting it to the investigators only no reporters and whenever a curious reporter turned up they would name and address an we will send a complete technical report in the mail now go away we are busy.
This allowed legal to completely rewrite out all the bad bits and self incriminating evidence period before final public release .
The Comet investigation was complete thorough and very much out in the open at all times and information was released regularly .
This closed shop investigation gave out the odd snippet or tidbit , since the pilots were proclaimed heroes on day one , oh curses we can't blame them any more can we !
But then again the most dangerous time for any twin engine aircraft not far off stalling speed and low altitude under 1500 feet is asymetric thrust as any twin engine prop pilot will say on take off on full power when one engine suddenly fails at end of runway "We just bought the farm oh crap " as they have no more room to move due low speed sudden spin right or left and no altitude to trade for speed either .
Now since modern jets have both smart and dumb computer chips with both feed forward and feedback loops at the same time thus if one engine began to speed up but the second one says after you and then they both get in that loop and say to each other no you first then me vice versa and suddenly you have a live logic bomb go off if you have no loop limit instruction that says crap emergency firewall all engines now not later when both of you can't make up your mind as both are waiting for each other to spool up in a situation that will never happen hence just above idle speed thrust limit . Since the master electric switches and relays were activated to cut all power to everything due to ten tonnes of flammable Jet A sloshing around on the ground this would wipe the logic bomb off all the computers as after ten minutes they forget all register instructions held in the stack as the temorary memory is flushed from lack of power .
The other aspect is that most people regarding major aircraft incidents tend to remember the first rushed headlines and thereafter do not follow up unless spoon fed hence the goldfish memory syndrome which of course plays into the hands of those that seek cover up first of which Boeing is well versed in for decades since 1932 !
Choices ?
Recipe for disaster
Take 300,000 parts jet fuel, a dash of dry vermouth, stir with ice and sieve into a cold fuel tank, add an olive to taste, for the perfect Mile-high Martini, mmm goes down smoooth (if slightly short)
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