Quote from
Bis47 [Feb26/21:42]:
More likely, the flow fuel restriction problem was there well before the demand for higher engine output occured on short final. Maybe the fuel flow started to be restricted (cold related - any kind fuel of contamination, make you choice : ice, wax, bioslush ...) much earlier in the descent. The restriction built up slowly, somewhere between the LP pump in the wing fuel tank and the engine HP fuel pump. In a very cold spot? In a bend? Idlle fuel flow and very low temps at TOD might be a factor. Everything almost symetric (same cause, same effects). The restriction went unnoticed as long as only minimum fuel flow was required. Then ... when more fuel was required, i-e when the valves downstream the HP pump opened, the engines initialy accellerated, burning all the available fuel in the line, until the fuel flow became regulated by the fuel restriction upstream.
[Unquote]
Bien ecrit en Anglais, Monsieur/Madame... I certainly would not want to test my French in argument on this forum.
The problem we all have is that we do not have access to the FDR/QAR.
And the AAIB is not telling us if thrust above idle was used at any time during the descent. All they have said is that "
the A/C entered the hold at Lambourne at FL110; it remained in the hold for approximately 5 minutes, during which time it descended to FL90."
So they descended only 2000 ft in 5 mins (average of 400 ft/min), presumably at a speed below 250 kts. At that speed at idle power, you would expect, say, 2000 ft/min. But we don't know if they were slowing down at the same time, in which case they might not have needed extra thrust.
What happened after they left the hold is also for us to guess. But at LHR at midday it is fairly unusual to fly at idle thrust all the way from leaving the Lambourne hold to the intercept of the ILS glide-slope. [Once you are on the glide-slope, you have a better chance of avoiding thrust above idle, as you are - to oversimplify - generally slowing down.]
To sum up: we don't know.