Text in force at CS25-28: from CS25-0, effective 17 Oct 2003.
(See AMC 25.607)
(a) Each removable bolt, screw, nut, pin or other removable fastener must incorporate two separate locking devices if –
(1) Its loss could preclude continued flight and landing within the design limitations of the aeroplane using normal pilot skill and strength; or
(2) Its loss could result in reduction in pitch, roll or yaw control capability or response below that required by Subpart B of this CS–25.
(b) The fasteners specified in sub-paragraph (a) of this paragraph and their locking devices may not be adversely affected by the environmental conditions associated with the particular installation.
(c) No self-locking nut may be used on any bolt subject to rotation in operation unless a non-friction locking device is used in addition to the self-locking device.
ED Decision 2003/002/RM · Source