14 CFR § 27.672

A warning which is clearly distinguishable to the pilot under expected flight conditions without requiring the pilot's 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 is unaware of the failure. Warning systems must not activate the control systems.

The design of the stability augmentation system or of any other automatic or power-operated system must allow initial counteraction of failures without requiring exceptional pilot skill or strength by overriding the failure by movement of the flight controls in the normal sense and deactivating the failed system.

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

The rotorcraft is safely controllable when the failure or malfunction occurs at any speed or altitude within the approved operating limitations;

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

The trim and stability characteristics are not impaired below a level needed to permit continued safe flight and landing.