It only takes one small bug that only occurs when a very rare set of conditions are met in the code and you've got a non repeatable and potentially dangerous incident. No computer code is 100% bug free and the flight systems on a 777 will be no exception. Getting rid of obvious bugs is easy - getting rid of these sorts is damned hard. Also AFAIK Boeing don't use separate systems designed by separate teams so any bug in the code will occur in the backup systems too.

courtesy of New Scientist Letters

<http://www.newscientist.com/article/mg20026770.200-iced-fuel.html>

Now we have digital storage we can forget faster and more efficiently (Ok, that was a little cynical).

This happened about over Wyoming (lat 44.55, long -105.33), when they started the descent from FL390 to FL310.

http://tinyurl.com/6g9bbq

In the BA report, the findings indicated the the 777's engine control system properly commanded a thrust increase, so if it was a computer glitch, it would have been in the individual engine's computer. Having both engines have the same bug seems just as implausible. The recent cavitation they found in the fuel lines does suggest it could have been ice crystals. Interesting that it happened with the same Rolls-Royce engine model, though.

"Maybe the Beijing fuel has more water in it?"

Either that or all the melamine resin they added to boost its octane rating melted and clogged the fuel lines with lumps of plastic?

So now they run on water. Smart.

I don't know where within the engine system the flight data recorders get their feed of data or signals. But I would have thought they would be recording the actual messages over the databus which feed the engine control systems, so if an engine throttle demand message was transmitted then that would have been recorded, thus, if a software bug present in the engine control system resulted in a reduction in engine power, a reduced power setting message would have been transmitted over the bus, then this would be easily identified.

All you then need to do, is marry up the messages sent from the pilot's throttle levers over the databus and it should be easy to identify whether there was a software bug or not.

I suppose they could be a heater in to the fuel, prevent the ice forming, but you know what would happen, there would have to have a control system to turn the heater on when at high altitude in freezing conditions for a certain length of time and then turn it off when at lower altitude, so a computer...with a software bug... which would over heat the fuel and kaboom!

300 people dead and they're they'd be trying to track down an almost near impossible problem..back to square 1.

Computers...who needs 'em

Does this problem affect what the 77 pilots do? e.g. do they fly a high glide path when landing just-in-case the problem repeats? Just something else to add to the stress...

"like high quality av-gas"

Is there such a thing. I always thought that aero fuel was actually a lower grade fuel than the average car runs on.

"issued an airworthiness directive calling on operators of 777-200 and -300 aircraft equipped with Trent engines..."

... and running Windows Vista.

is basicly parafin

"Uncommanded rollback". Why can't they just say an engine stopped working?

"Uncommanded rollback". Why can't they just say an engine stopped working?

Because it didn't stop working. The engine didn't stall, it slowed down.

...why can't they just say an engine slowed down.

Is an 'uncommanded rollback' the same thing as the pilot losing control of the computer?

I find it amazing that everyone here has a speculation... surely the air accident investigators (of the Heathrow crash) *might* know better and be more qualified to say than people here?!

Perhaps they're actually Trent Reznor engines, and will fuck you like an animal.

I am loth to agree with the NTSB concerning engine fuel problems, however the explanation given for the apparent engine fuel starvation, is certainly more feasible than the puerile comment given by the UK AIB. I would have thought that by now defect monitoring procedures would be in place to obviate any further recurrence of this apparent phenomena.

I am not fully conversant with the B777 but I assume that the fuel heaters are sufficient for the job and I am sure that many sectors of high duration have been flown worldwide with this aircraft.

Let us hope that a workable solution to this problem will be forthcoming soon, for the sake of Air Safety.

Or you could follow my link, 2nd from top, and find a possible solution which doesn't involved heaters or software. And it's cheap. In fact here's the text in full so no-one has to follow a link.

"

If the Boeing 777 was indeed brought down at Heathrow by ice in its fuel (13 September, p 23), it would not be the first. One night in 1948 or 1949 four Royal Navy Attacker FB2 aircraft "fell out of the sky" at Royal Naval Air Station Milltown in Aberdeenshire, UK. Each had almost total loss of power in its single Rolls-Royce Nene 102 engine. In the morning we could find nothing wrong, apart from water in their low-pressure fuel filters when they were drained - about the same amount in each. They all started without trouble and were ground-run successfully. We concluded that the filters had iced up to the extent that the fuel flow had been severely impeded, but that overnight the ice had melted and the problem vanished.

Careful investigation seemed to exonerate home base fuelling arrangements from being the source of the water, so we had to look elsewhere. Much of the fuel in the Attacker was carried in an exposed, virtually uninsulated, ventral tank. This would suffer severe cooling at altitude.

Aviation fuel at room temperature contains dissolved water. We thought this might have come out of solution and formed ice on the filters. From then on it was standard procedure to add a small amount of methanol as antifreeze when refuelling the ventral tank. As far as I know, there were no further problems of this kind.

Since no one was injured and no damage done the press evinced no interest. Possibly by now there are not a lot of us left who remember the incident, but Rolls-Royce may still have the details in their archives.

"