Sec. 25.671 - General.
(a) Each control and control system must
operate with the ease, smoothness, and positiveness appropriate to its
(b) 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 the
malfunctioning of the system.
(c) The airplane must be shown by
analysis, tests, or both, to be capable of continued safe flight and
landing after any of the following failures or jamming in the flight
control system and surfaces (including trim, lift, drag, and feel
systems), within the normal flight envelope, without requiring exceptional
piloting skill or strength. Probable malfunctions must have only minor
effects on control system operation and must be capable of being readily
counteracted by the pilot.
(1) Any single failure, excluding
jamming (for example, disconnection or failure of mechanical elements, or
structural failure of hydraulic components, such as actuators, control
spool housing, and valves).
(2) Any combination of failures not
shown to be extremely improbable, excluding jamming (for example, dual
electrical or hydraulic system failures, or any single failure in
combination with any probable hydraulic or electrical failure).
(3) Any jam in a control position
normally encountered during takeoff, climb, cruise, normal turns, descent,
and landing unless the jam is shown to be extremely improbable, or can be
alleviated. A runaway of a flight control to an adverse position and jam
must be accounted for if such runaway and subsequent jamming is not
(d) The airplane must be designed so
that it is controllable if all engines fail. Compliance with this
requirement may be shown by analysis where that method has been shown to
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-23, 35 FR 5674, Apr. 8, 1970]