From MIL-F- 8785C (November 1980):
The change in yaw control force required to maintain attitude and sideslip shall not exceed 50 lbs for at least 5 seconds following:
1. Complete or partial loss of any function of the augmentation system following a single failure
2. Failure induced transient motions and trim changes either immediately after failure or upon subsequent transfer to alternate control modes
3. Configuration changes required or recommended following failure from FAR part 23:
A maximum of 150 lbs rudder pedal force is allowed for temporary application
A maximum of 20 lbs rudder pedal force is allowed for prolonged application
From FAR part 25:
A maximum of 150 lbs rudder pedal force is allowed for temporary application
A maximum of 20 lbs rudder pedal force is allowed for prolonged application
See Graphic