Originally Posted by
fgrieu
It is not clear (to me at least) how exactly the modified FC software (including tamed MCAS) can allow re-certification.
1) The original certification was heavily based on "grandfather rights" (an arrangement under which an aircraft can be approved per a variation of the original Type Certificate, simplifying certification and allowing to ignore some new requirements that the original did not have to meet). It is not sure to what degree the FAA will now allows that, much less all other certification authorities. Loss of all grandfather right would immensely complicate return to service, and the following.
2) MCAS is there to mitigate at least an unsatisfactory stick feel, which would be un-certifiable (without MCAS) under the current type certificate. Some speculate MCAS may even be required to mitigate a deeper nose-up tendency in some corners of the flight envelope. Thus MCAS should be highly reliable. But the current hardware is not meant for that: only two FC and AOA vanes, and some scenarios disable MCAS leaving the plane without its protection.
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This is my basic understanding too. However I think it might be the case that without MCAS, the MAX could not be certified today because of its pitch instability at high AoA. The MAX can’t be certified, anywhere, so long as it is dependent on AoA sensors for pitch stability in parts of the envelope, and only has two. To be certified, it has to have three. Yes I’m sure you could code laws to figure out which sensor is lying and which isn’t by comparison with the AHRS or whatever but no-one will certify that.
So the MAX will never fly again in commercial operation until it gets a third AoA sensor, the necessary flight control system to use three, and recertification. That’s a couple of years, at least. Heck, it might even be that it just can’t be certified. An Airbus in Direct Law is still certified...