MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures Mk II

[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.

3) The elevator can't be actuated manually (using trim wheel) in some (abnormal) conditions of the flight envelope (heavy mistrim at high speed), because the muscular force of the pilots is just not high enough. This always has been a serious issue with the 737, worsened with design changes (smaller trim wheel) of the NG also applying to the MAX. There is evidence that this issue was involved in the ET302 crash. Partial mitigation (yoyo maneuver) is not longer taught to pilots, many simulators do not attempt to simulate trim wheel force, and it surfaced that those that do had not been properly simulating that.

4) It surfaced that in the opinion of a panel of FAA engineers, the MAX did not meet standards of protection against shrapnel that could be thrown by engine malfunction and could severe essential cables, leading to loss of control: the larger engines increase the risk, and the standards became more stringent. This judgment was apparently overruled, but the facts remains, and 1 seems to make it worse from a re-certification standpoint.

What's Boeing plan on these items ? I vaguely see a tenable position that with extra pilot qualification, the plane is flyable with MCAS disabled, and pilots have time enough to react so that the plane does not enter the abnormal conditions making the trim wheel inop. Can that can take care of 2/3, facing 1? And what about 4 facing 1?