269
Federal Aviation Administration, DOT
§ 25.677
electrical or hydraulic system failures,
or any single failure in combination
with any probable hydraulic or elec-
trical failure).
(3) Any jam in a control position nor-
mally encountered during takeoff,
climb, cruise, normal turns, descent,
and landing unless the jam is shown to
be extremely improbable, or can be al-
leviated. A runaway of a flight control
to an adverse position and jam must be
accounted for if such runaway and sub-
sequent jamming is not extremely im-
probable.
(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 be reliable.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–23, 35 FR 5674, Apr. 8,
1970]
§ 25.672
Stability augmentation and
automatic and power-operated sys-
tems.
If the functioning of stability aug-
mentation or other automatic or
power-operated systems is necessary to
show compliance with the flight char-
acteristics requirements of this part,
such systems must comply with § 25.671
and the following:
(a) A warning which is clearly distin-
guishable to the pilot under expected
flight conditions without requiring his
attention must be provided for any
failure in the stability augmentation
system or in any other automatic or
power-operated system which could re-
sult in an unsafe condition if the pilot
were not aware of the failure. Warning
systems must not activate the control
systems.
(b) The design of the stability aug-
mentation system or of any other auto-
matic or power-operated system must
permit initial counteraction of failures
of the type specified in § 25.671(c) with-
out requiring exceptional pilot skill or
strength, by either the deactivation of
the system, or a failed portion thereof,
or by overriding the failure by move-
ment of the flight controls in the nor-
mal sense.
(c) It must be shown that after any
single failure of the stability aug-
mentation system or any other auto-
matic or power-operated system—
(1) The airplane is safely controllable
when the failure or malfunction occurs
at any speed or altitude within the ap-
proved operating limitations that is
critical for the type of failure being
considered;
(2) The controllability and maneuver-
ability requirements of this part are
met within a practical operational
flight envelope (for example, speed, al-
titude, normal acceleration, and air-
plane configurations) which is de-
scribed in the Airplane Flight Manual;
and
(3) The trim, stability, and stall char-
acteristics are not impaired below a
level needed to permit continued safe
flight and landing.
[Amdt. 25–23, 35 FR 5675 Apr. 8, 1970]
§ 25.675
Stops.
(a) Each control system must have
stops that positively limit the range of
motion of each movable aerodynamic
surface controlled by the system.
(b) Each stop must be located so that
wear, slackness, or take-up adjust-
ments will not adversely affect the
control characteristics of the airplane
because of a change in the range of sur-
face travel.
(c) Each stop must be able to with-
stand any loads corresponding to the
design conditions for the control sys-
tem.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–38, 41 FR 55466, Dec. 20,
1976]
§ 25.677
Trim systems.
(a) Trim controls must be designed to
prevent inadvertent or abrupt oper-
ation and to operate in the plane, and
with the sense of motion, of the air-
plane.
(b) There must be means adjacent to
the trim control to indicate the direc-
tion 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 adjust-
ment. The indicator must be clearly
marked with the range within which it
has been demonstrated that takeoff is
safe for all center of gravity positions
approved for takeoff.
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