14 CFR § 25.671

Each flight control system must operate with the ease, smoothness, and positiveness appropriate to its function. The flight control system must continue to operate and respond appropriately to commands, and must not hinder airplane recovery, when the airplane is experiencing any pitch, roll, or yaw rate, or vertical load factor that could occur due to operating or environmental conditions, or when the airplane is in any attitude.

Each element of each flight control system must be designed, or distinctively and permanently marked, to minimize the probability of incorrect assembly that could result in failure or malfunctioning of the system. The applicant may use distinctive and permanent marking only where design means are impractical.

The airplane must be shown by analysis, test, or both, to be capable of continued safe flight and landing after any of the following failures or jams in the flight control system within the normal flight envelope. Probable malfunctions must have only minor effects on control system operation and must be capable of being readily counteracted by the pilot.

Any single failure, excluding failures of the type defined in § 25.671(c)(3);

Any combination of failures not shown to be extremely improbable, excluding failures of the type defined in § 25.671(c)(3); and

Any failure or event that results in a jam of a flight control surface or pilot control that is fixed in position due to a physical interference. The jam must be evaluated as follows:

The jam must be considered at any normally encountered position of the control surface or pilot control.

The jam must be assumed to occur anywhere within the normal flight envelope and during any flight phase except during the time immediately before touchdown if the risk of a potential jam is minimized to the extent practical.

In the presence of the jam, any additional failure conditions that could prevent continued safe flight and landing must have a combined probability of 1/1000 or less.

If all engines fail at any point in the flight, the airplane must be controllable, and an approach and flare to a landing and controlled stop, and flare to a ditching, must be possible, without requiring exceptional piloting skill or strength.

The airplane must be designed to indicate to the flightcrew whenever the primary control means is near the limit of control authority.

If the flight control system has multiple modes of operation, appropriate flightcrew alerting must be provided whenever the airplane enters any mode that significantly changes or degrades the normal handling or operational characteristics of the airplane.