| Topic: | Re:Re:Re:BA Flight Lands Short of Runway at Heathrow | |
| Posted by: | Tim Henderson | |
| Date/Time: | 24/01/08 22:41:00 |
| The thread I have been following included contributions from a commercial pilot who made the comment on the pics : Further on the accident: new pictures just released show the aircraft with all lighting on, no RAT deployed, and the APU door shut just before landing, so the engines (or at least one of them) were probably still running at or near idle at the point the picture was taken. This may reinforce the fuel waxing or contamination theories. It seems highly unlikely that the independent FADECs, and the independent methods of transmitting throttle demands to the engines both failed at the same time. He had earlier proposed fuel waxing as a likely major contributor: I suspect that the first point of investigation will be fuel waxing, caused by exceptionally low temperatures en-route from China. The temperature at FL380 was around -70C for much of the last two or three hours of flight. The fuel regularly uploaded in China is Jet A1, which has a freezing point of -47C. With skin heating, the Total Air Temperature (TAT) (the ambient air temperature as modified by skin heating) would have been around -50C. The B777 tanks are a little better insulated than ours, but the fuel temperature would have been below -40C, I suspect. Whether this would cause a problem would depend on the rapidity of the descent and how much opportunity the fuel had to warm up as the TAT rose. The tendency to wax would also depend how much water was present in the fuel (there's always some). Water drain checks would have been carried out in Beijing, but it wouldn't be the first time they hadn't been carried out correctly, or that insufficient water was drained. The effect of fuel waxing is pretty instant when it happens: a friend of mine lost all four engines on a Hercules from this, back in 1982. Luckily for him, he was in the tropics and the fuel was able to heat up sufficiently in the descent for a disaster to be averted - but not by much. They decended from FL270 to 5000' in the process of recovering the engines. |