AAIB wording
Hi Phil,
Re. your #54, I must admit that, strictly speaking, you are right: their assertion "as previously reported" does not stand up to scrutiny of the rest of the paragraph.
We now know that an autothrottle demand for more thrust at about 600 ft achieved a response from both engines, but this was short-lived. The auto throttle would continue to send a series of demands (presumably, many times per second) until both engines achieved the desired thrust setting. We are not told if that was ever achieved, and in any case the 'spool-up' was short-lived. The right engine decelerated after 3 seconds (T+3 secs)
During the following 8 seconds, as the airspeed decayed, the autothrottle would have been demanding more and more thrust. This would be reflected, on the B777, by both throttle levers moving progressively forward, and the handling pilot would have been aware of this (as he endeavoured to keep the A/C straight). At some stage, the crew augmented the autothrottle demands by pushing the throttle levers further forward. Nevertheless, at T+11 seconds, the left engine decelerated to join the left one at something above flight-idle, and the airspeed would have been decaying faster.
What we do not yet know is: what happened earlier during the descent and approach? Could the demand for more thrust at T+0 have been the first since top-of-descent? On a daytime arrival into LHR, that would be (sadly) a very rare event. So, assuming thrust above idle was needed earlier (e.g., on initial approach, or to stabilise at 160 kts till 4 miles for ATC spacing) how did the engines respond to the autothrottle demands?
If the engines had gradually been contaminated with dirty or waxed fuel, would this not have been revealed earlier? Why did the two engines suffer no apparent problems until 600 ft, and then - despite feeding from separate tanks - only 8 seconds apart?
Re. the engines' differing fan damage, as seen in the photos, there are several things we don't know:
When did the left gear collapse?
When did each pod settle firmly enough on the ground to deform its fan intake?
When did the crew close the engine master switches (to "CUTOFF")?
Chris