Page 139 of the final report:
Actions of the co-pilot
The co-pilot initially believed he had disconnected the autopilot at the intended height on the approach in order to carry out a manual landing on Runway 27L. However, as the aircraft descended through 600 ft he became aware of a problem with the engines, indicated by a split in the thrust lever positions. It is likely that, in attempting to understand the sudden and unprecedented problem with which he was presented he was distracted and thus omitted to disconnect the autopilot at this point.
Engine power had now reduced to a level at which the aircraft was losing airspeed and it started to descend below the glideslope. As the autopilot had remained engaged it attempted to maintain the ILS glide path by increasing the aircraft’s pitch attitude. This led to a further gradual reduction of airspeed, the initial ‘airspeed low’ master caution and the eventual triggering of the stall warning stick shaker. It was at this stage the co-pilot promptly pushed the control column forward, leading to the disconnect of the autopilot. However, the aircraft was now only 150 ft above the ground
Boeing Non-Normal Situation Guidelines for automated approach monitoring, issued March 2009 (not mentioned in the AAIB report):
• NON-NORMAL RECOGNITION:
o The crewmember recognizing the malfunction calls it out clearly and
precisely.
• MAINTAIN AIRPLANE CONTROL:
o It is mandatory that the Pilot Flying (PF) fly the airplane.
• ANALYZE THE SITUATION:
o Any further action should only be initiated after the malfunctioning
system has been positively identified.