Sec. 23.677 - Trim systems.
(a) Proper precautions must be taken to
prevent inadvertent, improper, or abrupt trim tab operation. There must be
means near the trim control to indicate to the pilot the direction of trim
control movement relative to airplane motion. In addition, there must be
means to indicate to the pilot the position of the trim device with
respect to both the range of adjustment and, in the case of lateral and
directional trim, the neutral position. This means must be visible to the
pilot and must be located and designed to prevent confusion. The pitch
trim indicator must be clearly marked with a position or range within
which it has been demonstrated that take-off is safe for all center of
gravity positions and each flap position approved for takeoff.
(b) Trimming devices must be designed so
that, when any one connecting or transmitting element in the primary
flight control system fails, adequate control for safe flight and landing
is available with --
(1) For single-engine airplanes, the
longitudinal trimming devices; or
(2) For multiengine airplanes, the
longitudinal and directional trimming devices.
(c) Tab controls must be irreversible
unless the tab is properly balanced and has no unsafe flutter
characteristics. Irreversible tab systems must have adequate rigidity and
reliability in the portion of the system from the tab to the attachment of
the irreversible unit to the airplane structure.
(d) It must be demonstrated that the
airplane is safely controllable and that the pilot can perform all
maneuvers and operations necessary to effect a safe landing following any
probable powered trim system runaway that reasonably might be expected in
service, allowing for appropriate time delay after pilot recognition of
the trim system runaway. The demonstration must be conducted at critical
airplane weights and center of gravity positions.
[Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as
amended by Amdt. 23-7, 34 FR 13091, Aug. 13, 1969; Amdt. 23-34, 52 FR
1830, Jan. 15, 1987; Amdt. 23-42, 56 FR 353, Jan. 3, 1991; Amdt. 23-49, 61
FR 5165, Feb. 9, 1996]