Without the ILS, it's likely they tried VNAV approach. This, however, does not always work in SFO (FMS glitch, witnessed by some airlines), and the plane can go into VNAV ALT instead of VNAV PTH descent.
It may be that the pilot got high on approach (maybe for the reason stated above, or maybe just trying to fly visually).
Next, he possibly selected FLCH to get down. If he then got too low and tried to recover the profile, this might explain why he disconnected the A/P.
If he then flew in manual without disconnecting the FD, two things would happen.
First, the elevators, hitherto controlling speed (in FLCH), are now being used to control pitch (F/D would still be demanding attitude for speed control in FLCH) and, two, the thrust, hitherto controlling ROD (in FLCH this could mean IDLE or 'HOLD' IDLE), is now 'controlling' (not much control if in IDLE) speed.
But, and this is the BIG but, there will be no automatic speed protection or speed control, for that matter, without pilot input, regardless of whether the A/T is engaged or not (in this case, it was).
It's easy to imagine the pilot, late in the approach, struggling to recover the path with pitch inputs, staring outside, not keeping an eye on his speed, believing he has A/T speed protection, and not realizing that the throttles are near idle and will stay there without his input. Classic stall scenario.
Educated guess.
Last edited by 'round midnight; 12th Jul 2013 at 03:36.