rondun

A special bulletin has been released today by the AAIB:

here


And the update of 12th May 2008

Interim report 1 09/08

Interim Report 2 03/09

Rolling-Thunderbird

Interesting 'snippets' from the report


"Detailed examination of both the left and right engine high
pressure fuel pumps revealed signs of abnormal cavitation
on the pressure-side bearings and the outlet ports. This
could be indicative of either a restriction in the fuel
supply to the pumps or excessive aeration of the fuel. The
manufacturer assessed both pumps as still being capable
of delivering full fuel flow."

"Investigations are now underway in an attempt to
replicate the damage seen to the engine high pressure
fuel pumps, and to match this to the data recorded on the
accident flight. In addition, comprehensive examination
and analysis is to be conducted on the entire aircraft and
engine fuel system; including the modelling of fuel flows
taking account of the environmental and aerodynamic
effects."

shoey1976

http://www.aaib.dft.gov.uk/cms_resou...8%20G-YMMM.pdf

what does everybody think?
ian shoesmith
bbc news
[email protected]

shoey1976

can somebody give an explanation of what these valves are, and how they play an important role, please?

Hand Solo

I think the previous poster who suggested fuel starvation is reading something into the report that isn't there. There's nothing I can see in this report that gives an indication of the cause but it does rule some things out. As to the debris found in the tanks, it's undesirable but not uncommon or necessarily dangerous. Aircraft have been leaving the Boeing plant with bigger bits of FOD than those in the tanks for years.

Shoey - the spar fuel valve is in the fuel tank and the fuel passes through this first on the way to the engine. It then passes through various fuel pumps, heat exchangers and other paraphernalia before it arrives at the engine fuel valve, through which is passes into the engine to be burned. It would appear in this instance that there was a rupture somewhere between the engine and the spar fuel valve, allowing fuel to leak through the open spar fuel valve and out of the system even though the engine fuel valve was closed.

Feathers McGraw

So, with the exception of the HP fuel pump damage, which might be due to insufficient fuel supply or aerated fuel (or something else which escapes me just now) everything was working normally. The FOD in the tanks is probably not sufficiently large to block any of the exit screens/pipes, so what else could cause fuel starvation?

I can almost hear the sound of heads being scratched from here.

mono

Though I must say that every a/c I have worked on. Pulling the fire handles activates the LP (spar valves) and HP (engine fuel valves)

You could have knocked me over sideways when I read that they weren't on the 777!!!???

lomapaseo

isn't this secondary to the ground impact and not in the causal chain of the accident?

Hand Solo

Yes it is secondary, although it does have survivability aspects for the accident. For clarification I wasn't intending to suggest they contributed to the crash.

BoeingMEL

............ at least all that garbage about EMI can be buried..... as can fuel exhaustion, windshear, finger trouble, Gordon Brown's heavies... (IMHO you understand) Cheers bm

SILENT_BADGER

Yes it is secondary. The reason the report brought it up is because of the fuel that leaked during the evacuation.

The evacuation checklist aims to shut off things that could lead to fire or other dangers. BA's evacuation checklist has the captain switching off the fuel valves whilst the F/O does the engine fire handles which meant that if the F/O did his bit before the captain then the electric relay controlling the fuel valve would be isolated and the valve didn't close. So the report has issued a sensible recommendation that operators make sure their checklists do things in the right order. It also mentions that Boeing were already in process of changing all 777s so that the fire handles close the fuel valves as well as all the other disconnections so you wouldn't need to do switch the fuel valves separately.

Most other aircraft already have the fire handles/buttons doing all the isolation in one fell swoop already.

Cheers,
SB

booke23

The report also mentions a planned descent to FL315 due to "extreme cold"....which did not happen because of an ATC request.

Also mentioned was that later in the flight at FL380 over the Ural mountians the oat was -76. The met office decscribed this as "unusually low compared to the average, but not exceptional"

They seem to be considering the possibility of fuel icing, however the fuel never got below -37.

Puzzling indeed.

MungoP

What occurs to me when reading this report is just how intensive and detailed an accident investigation has to be.. and should humble some of the 'contributers' here who are repeatedly whinging about the lack of results... additionally, the AAIB is dealing with an a/c for the most part in one piece... just how awsome their task must be when dealing with scattered/burned wreckage begins to become apparant..

Hand Solo

I would hazard a guess that they had ruled out fuel icing based on the information in the report. The fuel never got lower than 20C above freeze point and I'm sure the inclusion of the information is to clarify that fuel freezing was highly unlikely to be a factor, just like they included the information about water in the tanks.

misd-agin

A/P kicked off at 175'. Airspeed down to 108Kts by 200' as the a/p tried to maintain the g/s.

Thank god the a/p kicked off.

nhs

MungoP

Couldn't agree more. I hope people remember also that this is not a complete investigation report, but one published rapidly due to public interest. The fact that they have already come up with advisory notices without finding a cause shows their attention to detail.
As a SLF I'm grateful they are there looking out for all of us.

I Just Drive

So the only manual flying part of the adventure was from < 200' then?

Mr @ Spotty M

Yes l was surprised about the Auto-pilot, not being a Pilot, l thought that you would disconnect ASAP, would the A/P keep raising the nose if it was not getting any more thrust.
I would like someone to explain if l am wrong please, l know hindsight is a great thing.

glad rag

Well thank heavens it went in on the undershoot. The combination of ruptured fuel tanks, ruptured O2 cylinders and an ignition source from contact with the runway are just too horrible to contemplate.

I Just Drive

Yes, the auto-pilot would try and keep the glide slope at the expense of the speed. (With no thrust)