Originally Posted by
FCeng84
With correct AOA supplied to the MCAS function,
There is the problem right from the very first assumption,
correct AoA data.
I don't think there is any disagreement about the need, intent and function of the MCAS. The issue appears to be this, on the surface its looks like a "quick and dirty" hack to compensate for an issue that cropped up in certification and testing, with the engineering failure mode analysis appearing to be deeply flawed. It was eminently foreseeable that one or both AoA sensors could provide erroneous or missing data due to mechanical or maintenance failure or physically by a birdstrike.
If you look at the Airbus (BTW, not a Bus fanboy, they had their own issues), there is clear guidance to to what happens to the flight controls with failure(s). A good example is the QRH flight control architecture reconfiguration diagram in the QRH, it tells you how the flight control system has reconfigured itself. On the other hand, the MCAS functionality looks to have been buried, with almost no references anywhere, it is almost as if Boeing had gone out of their way to deliberately obscure knowledge of this subsystem. Why? Because we don't want to overwhelm the pilots with information? Really?
Is it mentioned in the engineering manuals anywhere? If the maintenance staff had known about the interconnection between the AoA running the stab forward on it's own, would they have signed it off for a line flight? Was there a warning in the maintenance manual about the consequences of incorrect maintenance of the AoA probe? So many questions about this buried functionality that clearly has deep implications for the safe operations.
Source: Online
copy of an old A32x family showing flight control reconfiguration with failure cases.
A32x flight controls overview
