Sec. 25.677 - Trim systems.
(a) Trim controls must be designed to
prevent inadvertent or abrupt operation and to operate in the plane, and
with the sense of motion, of the airplane.
(b) There must be means adjacent to the
trim control to indicate the direction of the control movement relative to
the airplane motion. In addition, there must be clearly visible means to
indicate the position of the trim device with respect to the range of
(c) Trim control systems must be
designed to prevent creeping in flight. Trim tab controls must be
irreversible unless the tab is appropriately balanced and shown to be free
(d) If an irreversible tab control
system is used, the part from the tab to the attachment of the
irreversible unit to the airplane structure must consist of a rigid
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-23, 35 FR 5675, Apr. 8, 1970]