Originally Posted by
LNAV VNAV -
Any one can explain why an erroneous AoA input can cause an IAS disagreement? Aren’t the inputs to the airspeed indicators just the static and pitot pressures?
No the ASI is driven by the ADIRUs and they correct the inputs from the pitot and static ports using the AoA inputs. It is the ADIRU getting AoA disagree that alert to the airspeed being unreliable, I would have thought that the first check on unreliable airspeed in the Max would be set stab trim switches to CUTOUT that means manual trim but MCAS is now out of the loop.
I am surprised that after the Lion Air crash and the AD that any pilot on the Max would be unaware of the MCAS issue and have briefed accordingly before any flight about stab trim cutout if trimming became difficult - it is part of the standard runaway trip checklist. The fact that another crew had crashed and could have survived if they had switched stab trim to cutout should have concentrated minds.