Originally Posted by
BEagle
I read from the BBC:
If AoA sensor disagreement in future will disable MCAS, then that must surely mean that the aircraft is allegedly safe to fly without it?
Boeing also said that airlines which fit this 'upgrade' are to be required to 'give feedback on its performance'. Surely that's the job of Boeing's flight test department?
I can't see many passengers being happy to fly in a 737 Max ever again, no matter what 'upgrades' Boeing provides.
With regard to the acceptability of operating without a particular control system feature active, it all comes down to consideration of both the consequences of not having that feature and the rate of occurrence of not having that feature. In the case of MCAS, the function is designed to only act at higher AOA so for most flights it will not come alive. Combining the probability of being at an AOA where MCAS activates with the probability of an AOA sensor failure that would now be detected and lead to MCAS not being available must push the likelihood of not having MCAS when it would act out to a very low rate. The pilot assessment hazard level associated with not having MCAS must be low enough to allow the resulting unavailability rate.
Another example of is the impact pressure schedule for the variable column feel on the 737. There are two separate feel units that are each driven by their own air data sensors. If a failure of one occurs (let's say its probe gets plugged as a result of hitting a bird) the column feel characteristics will be degraded - likely to a degree that would not support certification with respect to every day operation. Piloted evaluation, however, has shown that at the presumed rate of hitting a bird such that the probe is plugged the associated degradation in column feel is acceptable. In a more remote event hitting a flock of birds might plug both probes causing both feel units to behave improperly and the feel characteristic to degrade much more. Pilot evaluation of the change in feel characteristics with both feel units degraded has shown that it is acceptable given the probability of occurrence of that event.