BA 777 Update

[Doug Taylor]

Accident to a Boeing 777-236, G-YMMM, on 17 January 2008 at 1243 hrs

Initial Report Update 23 January 2008

Since the issue of the Air Accidents Investigation Branch
(AAIB) 1st Preliminary Report on Friday 18th January 2008
at 1700 hrs, work has continued on all fronts to identify why
neither engine responded to throttle lever inputs during the
final approach. The 150 tonne aircraft was moved from the
threshold of Runway 27L to an airport apron on Sunday
evening, allowing the airport to return to normal operations.

The AAIB, sensitive to the needs of the industry including
Boeing, Rolls Royce, British Airways and other Boeing 777
operators and crews, is issuing this update to provide such
further factual information as is now available.

As previously reported, whilst the aircraft was stabilised
on an ILS approach with the autopilot engaged, the
autothrust system commanded an increase in thrust
from both engines. The engines both initially responded
but after about 3 seconds the thrust of the right engine reduced.

Some eight 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.

Recorded data indicates that an adequate fuel quantity was
on board the aircraft and that the autothrottle and engine
control commands were performing as expected prior to, and
after, the reduction in thrust.

All possible scenarios that could explain the thrust
reduction and continued lack of response of the engines to
throttle lever inputs are being examined, in close
cooperation with Boeing, Rolls Royce and British Airways.
This work includes a detailed analysis and examination of
the complete fuel flow path from the aircraft tanks to the
engine fuel nozzles.

Further factual information will be released as and when
available.

The AAIB will continue to release all information on the
progress of their investigation.

[the_dmn8tr]

It will be interesting to find out what happened with the throttles

[jtrain609]

I wonder how big the lawsuit against Boeing, Rolls Royce and BA will be.

[skyrunner1500]

I doubt it has to do anything with the engines. Otherwise they wouldn't let all other 777 worldwide continue to fly.

[SteveC]

[speculation mode]

Fuel problem.

[/speculation mode]

[SkyCougar]

Originally Posted by SteveC

[speculation mode]

Fuel problem.

[/speculation mode]

As in contaminated fuel?

[jtrain609]

Dunno what the fuel could be contaminated with. Jet engines will burn just about anything, so having something such as water in the fuel won't hurt a jet engine unless for some God forsaken reason there happens to be enough water so as to put out the fire in the engine. Heck, I'm pretty convinced a PT-6 could be run on windex and vodka.

[FiveO]

They must have missed one of the fuel sumps in the wing on the walk around.

[Screaming_Emu]

Originally Posted by FiveO

They must have missed one of the fuel sumps in the wing on the walk around.

And forgot to do a mag check before takeoff

[FiveO]

Originally Posted by Screaming_Emu

And forgot to do a mag check before takeoff

Oh yes... of course.

[Duck_Twacy]

I hate computers...

I bet the programmer working on the fuel control unit was a short timer when he wrote that code.

Any code written once you've turned in your notice is crap, TRUST ME on this one....

Seriously though, with these FBW aircraft, think about it. One ticked off programmer or software bug could ruin your day.

[Seggy]

I read a thread on PPW where a similar instance happened to an Air Force Tanker.

Basically what happened is that the anti-icing fuel additives where not added and the fuel gelled up at altitude in the cold atmosphere. They did an idle decent and when they went to add power NOTHING happened.

Once again it is speculation. It is going to be interesting.

[Nick]

Originally Posted by Seggy

I read a thread on PPW where a similar instance happened to an Air Force Tanker.

Basically what happened is that the anti-icing fuel additives where not added and the fuel gelled up at altitude in the cold atmosphere. They did an idle decent and when they went to add power NOTHING happened.

Once again it is speculation. It is going to be interesting.

In looking up "prist" after reading this, here is a page I found that might be of interest to anyone curious about the basics of this subject:

http://www.csdinc.org/prist/prod_info.htm#Why

I always heard corporate pilots saying "with prist" on some fuel orders. I know little about it -- does it get mixed into the airport fuel supplies at places like Beijing and the rest of the world's airline hubs?

[JaceTheAce]

Throttles?

[NightCargo]

Originally Posted by Doug Taylor

Recorded data indicates that an adequate fuel quantity was on board the aircraft and that the autothrottle and engine control commands were performing as expected prior to, and after, the reduction in thrust.

Anyone else find this part interesting?

[flyover]

Theories propounded by crew include the possible presence of water in the tanks that, having become frozen during the intense cold-soak period of the flight, partially melted and formed a slush that could have partially blocked the fuel lines. Sources also tell The DAILY that upper air temperatures over Russia and northern Europe were extremely cold on the day of the accident. Information from other crews coming from Asia on Jan. 17 encountered extremely low temperatures in the -70 to -75 degrees C. range, resulting in fuel temperatures dipping into the -40s. European upper air temperatures also indicate the last 6.5 hours of the inbound China flight would have been flown at an outside air temperature of -60 deg. C. or lower. Although this would have resulted in fuel temperatures on approach in the -35 degrees C range, this would not normally constitute a problem unless, potentially, contaminants were present.


Man, that is cold. I've never seen temps colder than about -65 but in that case, after about 5 hours in it, we had an engine that wouldn't increase thrust after an intermediate level off during descent. It just stayed at descent idle thrust regardless of throttle position. After a short time it corrected itself and the later conclusion was possible icing in a small fuel line. At the time I thought how exciting it would have been if all 4 engines did it at the same time. In this BA case it looks like 100% of the engines had the same problem at the same time.

[mrivc211]

Originally Posted by jtrain609

I wonder how big the lawsuit against Boeing, Rolls Royce and BA will be.

I wondered this at one point too, but I found outthat the law limits the amount they can be sued for. Go figure.

[seagull]

Originally Posted by Nick

does it get mixed into the airport fuel supplies at places like Beijing and the rest of the world's airline hubs?

No, it's not necessary for most larger jets, as they have fuel heating systems installed in the fuel lines. More problematic is fuel cooling to the point it is like jello on long haul ops. It can be thick enough so the fuel pumps won't pull it in. I would not imagine that would be true in this case, as it should have warmed on the way down, and the fuel low temp sensors would have alerted the crew well before their approach.

[flyover]

Originally Posted by seagull

No, it's not necessary for most larger jets, as they have fuel heating systems installed in the fuel lines. More problematic is fuel cooling to the point it is like jello on long haul ops. It can be thick enough so the fuel pumps won't pull it in. I would not imagine that would be true in this case, as it should have warmed on the way down, and the fuel low temp sensors would have alerted the crew well before their approach.

But it does raise questions about the condition of the fuel loaded in China. The temperatures they encountered would have produced tank temperatures approaching the freeze point of Jet-A. If the fuel was contaminated or in some other way compromised, the slush in the tank scenario is plausible.

[seagull]

Originally Posted by flyover

But it does raise questions about the condition of the fuel loaded in China. The temperatures they encountered would have produced tank temperatures approaching the freeze point of Jet-A. If the fuel was contaminated or in some other way compromised, the slush in the tank scenario is plausible.

PEK does utilize Jet-A1, as I recall, which has a freeze point not above -47c. I am not familiar with how the fuel system keeps the fuel stirred up on the 777, but I imagine it is not unlike the MD11, where fuel temp should not be an issue, at least ordinarily.

Also, with the volume of fuel they pump in PEK, I would think that other contamination is less likely. Having said that, it does happen, and I know of a couple of events, first hand.

[LoadMasterC141]

Particle Contaminated fuel can clog fuel nozzles as I recall.

Does this make any sense? I hear that there are tolerances how long particle contaminated fuel can work in newer jet engines..............

[rjmore]

I think if it were a fuel contamination problem there would have been other instances of this occurring out of PEK that day. On the 744 if we get low fuel temps we have to resolve the issue as quickly as possible. We can usually accomplish this by speeding up and/or descending.

I encountered outside temps of -75C a few weeks ago over northern Canada. We sped up and descended. This kept the fuel temp at roughly -36C until we came out of that cold air. Initially we sped up from .83 to .87 and that started to do the trick. Keep in mind, we were fueled in DFW with Jet A not A1. Our procedure is that we must have been fueled three sectors with A1 before we can use that -47C as a freeze point.

Could be that the aircraft had been fueled with Jet A at some point in the past couple days and a bit of it was still in the tanks? Not sure what MMO is on the 777 but they may not have been able to speed up enough to get above -40C. Having been fueled with Jet A1 out of Beijing, they may not have been concerned with it. It would be interesting to see where that aircraft had been over the previous few days.

[seagull]

Originally Posted by rjmore

I think if it were a fuel contamination problem there would have been other instances of this occurring out of PEK that day. On the 744 if we get low fuel temps we have to resolve the issue as quickly as possible. We can usually accomplish this by speeding up and/or descending.

I encountered outside temps of -75C a few weeks ago over northern Canada. We sped up and descended. This kept the fuel temp at roughly -36C until we came out of that cold air. Initially we sped up from .83 to .87 and that started to do the trick. Keep in mind, we were fueled in DFW with Jet A not A1. Our procedure is that we must have been fueled three sectors with A1 before we can use that -47C as a freeze point.

Could be that the aircraft had been fueled with Jet A at some point in the past couple days and a bit of it was still in the tanks? Not sure what MMO is on the 777 but they may not have been able to speed up enough to get above -40C. Having been fueled with Jet A1 out of Beijing, they may not have been concerned with it. It would be interesting to see where that aircraft had been over the previous few days.

True, although it would have mixed, and the pour point temp would have been inbetween the two, somewhere. Recall that -40 is the max temp for JetA, and that it can be colder. LAX JetA, for example, averages closer to -50c. To my knowledge, only NWA actually tests the fuel and uplinks the actual temp to the International flights, after departure.

[Minuteman]

I'd be surprised if it was fuel. Like rjmore said, there should have been problems experienced by other flights as well. If fuel was a cause, I would have expected the problem to manifest more gradually and asymmetrically: one engine goes to a reduced thrust, recovers, declines, then the other has trouble later.

Also, the engines were producing thrust above flight idle, but did not respond to commanded changes.

[flyover]

Originally Posted by Minuteman

Also, the engines were producing thrust above flight idle, but did not respond to commanded changes.

Which is exactly how my engine behaved after a long cold-soak.

Different engines, different fuel system, but the kinds of temperatures they were subjected to on their flight were definitely toward the edge of the envelope. Not routinely experienced and certainly a possible factor.

It's almost never just one thing. If it is a fuel contamination issue, it could be that if they had operated at more "normal" temperatures that nothing would have happened. It's all conjecture for now, but given that several of these airplanes will be configuring for approach today and the crews will be watching to see if the thrust comes up as commanded, conjecture is inevitable.