Ethiopian airliner down in Africa

[Ian W]

Originally Posted by fdr

§ 25.672 Stability augmentation and automatic and power-operated systems

If the functioning of stability augmentation or other automatic or power-operated systems is necessary to show compliance with the flight characteristics requirements of this part, such systems must comply with § 25.671 and the following:

(a) A warning which is clearly distinguishable to the pilot under expected flight conditions without requiring his attention must be provided for any failure in the stability augmentation system or in any other automatic or power-operated system which could result in an unsafe condition if the pilot were not aware of the failure. Warning systems must not activate the control systems.

(b) The design of the stability augmentation system or of any other automatic or power-operated system must permit initial counteraction of failures of the type specified in § 25.671(c) without requiring exceptional pilot skill or strength, by either the deactivation of the system, or a failed portion thereof, or by overriding the failure by movement of the flight controls in the normal sense.

(c) It must be shown that after any single failure of the stability augmentation system or any other automatic or power-operated system -

(1) The airplane is safely controllable when the failure or malfunction occurs at any speed or altitude within the approved operating limitations that is critical for the type of failure being considered;

(2) The controllability and maneuverability requirements of this part are met within a practical operational flight envelope (for example, speed, altitude, normal acceleration, and airplaneconfigurations) which is described in the Airplane Flight Manual; and

(3) The trim, stability, and stall characteristics are not impaired below a level needed to permit continued safe flight and landing.

[Amdt. 25-23, [url=https://www.law.cornell.edu/rio/citation/35_FR_5675]35 FR 5675 Apr. 8, 1970]

It all depends whether you believe the AOA vanes and system are part of the MCAS. Its like using an ASI display spec to regulate the pitot/static systems. MCAS worked precisely as it should - it was given the incorrect inputs. Inputs that were also used for ADIRUs and those systems provided a cacophony of warnings - for some reason their logic does not include an AOA disagree and that warning light is an 'optional extra'.

As was stated repeatedly on the AF447 thread AOA should be considered a non-optional display and AOA disagree should also be non-optional. An AOA disagree should result in the disabling of any system would operate dangerously. However, as was stated up thread a lot more logic could be used to identify and isolate the incorrect AOA. Only validated AOA information should be fed to systems or those systems disabled.