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The Bellinghman
Date: 2008-01-24 15:15
Subject: Update on the 777 crash landing
Security: Public
According to the BBC report

In its update, the AAIB said the Boeing's twin Rolls-Royce engines initially responded to the request for thrust, but after three seconds the thrust of the right engine reduced and after eight seconds there was a thrust reduction in the left one.

Recorded data shows the aircraft had enough fuel and its automatic throttle and engine control systems had worked as expected, the AAIB said.


Yet: Both engines [...] were still running when it came down

This is really beginning to sound like a fuel system problem to me. I assume they're now double checking to see whether there really was sufficient fuel in the tanks. After that, I'd be looking at the fuel pumps.
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Nicolai The Hand Grenade of Courteous Debate
User: _nicolai_
Date: 2008-01-24 15:20 (UTC)
Subject: (no subject)
Enough fuel in the correct tanks also. There was an incident to an Airbus A340 a year or two ago in which two engines ran down (one restarted) due to fuel mis-management caused by an error condition in the fuel management computers. The AAIB as usual went into detail. The root cause was a subtle logic error in which a failing fuel management computer was left to control the fuel supplies.
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The Bellinghman
User: bellinghman
Date: 2008-01-24 16:44 (UTC)
Subject: (no subject)
Yes, that's another thing to consider.
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Nicolai The Hand Grenade of Courteous Debate: B-17
User: _nicolai_
Date: 2008-01-25 07:38 (UTC)
Subject: (no subject)
Keyword:B-17
Reading up on it a bit more, the fuel system in the 777 seems to be less complicated than I had thought: unless it's a long-range aircraft (which this one appears not to be, it's a 777-200 as I understand) there are only three fuel tanks (one centre, two wing), making it harder to mess up fuel management than on some aircraft with 5 or 6 tanks.
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Artela
User: artela
Date: 2008-01-24 15:39 (UTC)
Subject: (no subject)
They also seem to say on the BBC site that 6 other of the same model of plane have had similar problems but only in one engine at a time... I would hope that they'll be considering some sort of recall / fix now they've had it happen in both engines on the same plane?
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Nicolai The Hand Grenade of Courteous Debate
User: _nicolai_
Date: 2008-01-24 16:37 (UTC)
Subject: (no subject)
Not sure where the BBC get the NTSB is saying that (a quick search of their database for 777 engine failures shows only one for a 777 since 1995). However, engine failures for one reason or another are not at all unheard of. Based on data from Wikipedia (the table of sales per year) we can say that there have been at least 4502 aircraft-years of operation of the 777. 6 engine failures would mean the average 777 would have to operate for a somewhat preposterous 750 years. Or to put it another way: in a 30-year operational life, most 777s would not have a single engine failure.
The number "6" must be considered in light of both the number of aircraft made, the time they have been made over, and the fact that they usually fly one or two long-haul flights each day.
The disturbing part of this accident is not that an engine failed, but that both failed. This has not happened to a 777 before as far as I know.
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The Bellinghman
User: bellinghman
Date: 2008-01-24 16:45 (UTC)
Subject: (no subject)
I'd love to know how many flight hours the 777 has accumulated so far.

Ah, apparently 3.6 million flight hours.

Edited at 2008-01-24 10:03 pm (UTC)
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Sion: car
User: sion_a
Date: 2008-01-24 16:49 (UTC)
Subject: (no subject)
Keyword:car
The Register goes into more detail about the other six incidents, albeit quoting from the Telegraph, so that information must be coming from somewhere.
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The Bellinghman
User: bellinghman
Date: 2008-01-24 16:38 (UTC)
Subject: (no subject)
I'd hope so, though I doubt they've been ignoring the previous incidents. They do need to know what the fix is to be, of course.

In the meantime, it's a pretty safe plane in general - something like 5000 operational years with this being the worst incident to date - so I wouldn't be terrified of getting in one.
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Erik V. Olson
User: erikvolson
Date: 2008-01-24 23:47 (UTC)
Subject: (no subject)
So far, no hull losses, and the only fatality was a door accident that blew a FA out of the door and onto the tarmac. That door is pretty high up.

I suspect this will be a hull loss. The A340 has a similar record (very few, non-flight related fatalites, one hull loss -- the Toronto crash for AF.)

I don't think it's fuel pumps -- the 777 only has three tanks, and there's multiple pumps per tank. Usually, when you lose both engines at the same time, it's either fuel starvation or fuel contamination.

here's the fuel panel for the 777. Note that each tank has two pumps, and there's a crossfeed set, so that any tank can feed any engine. By design, with all crossfeeds off, the left tank feeds the left engine, the right the right, and the center feeds both.

The only common point of failure I see is fuel quality. If fuel flow dropped, the Flight Management System would have been alarming -- and we'd have seen that on the black box recording. From what I've seen, it didn't.



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