‘F/O should have taken control.’
The investigation did consider this aspect; there were indications that the PM had the better understanding of the rapidly developing situation. However, whilst he could ‘see’ what the aircraft was doing, not knowing why might have delayed the choice of ‘drastic’ intervention after repeatedly alerting the PF to the abnormal condition (CVR).
The report discusses control force from the FDR which suggests that there was dual control input, even to the point of left / right control breakout - PF pushing, PM pulling, but the situation at that time was significant nose down attitude, speed increasing, and the trim moving fully forward.
The above indicates that the concept of monitoring and crew intervention cannot be assured in all situations.
The difficulty in identifying trim operation and position (as in the Max accidents) is explained, as is the mechanics of control forces and impossibility of effecting a recovery at low altitude, again as in the Max accidents. This point should be noted by regulators / operators if the 737 Max post MCAS mod, were to revert to a ‘near NG’ configuration, in that any assumption requiring quick identification and pilot action to intervene for a trim malfunction is misjudged given the findings in this accident.
Also see footnote #38 page 175.