Federal Aviation Administration, DOT

Section 25.391

the conditions specified in paragraph
(e) of this section. In addition, reasonable design precautions must be taken
to minimize the probability of parts
becoming detached and injuring occupants while in their seats.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-54, 45 FR 60172, Sept.
11, 1980; Amdt. 25-71, 55 FR 13477, Apr. 10,
1990; Amdt. 25-72, 55 FR 29776, July 20, 1990;
Amdt. 25-87, 61 FR 28695, June 5, 1996]

spaschal on DSK3GDR082PROD with CFR

Section 25.367 Unsymmetrical loads due to
engine failure.
(a) The airplane must be designed for
the unsymmetrical loads resulting
from the failure of the critical engine.
Turbopropeller airplanes must be designed for the following conditions in
combination with a single malfunction
of the propeller drag limiting system,
considering the probable pilot corrective action on the flight controls:
(1) At speeds between VMC and VD, the
loads resulting from power failure because of fuel flow interruption are considered to be limit loads.
(2) At speeds between VMC and VC, the
loads resulting from the disconnection
of the engine compressor from the turbine or from loss of the turbine blades
are considered to be ultimate loads.
(3) The time history of the thrust
decay and drag build-up occurring as a
result of the prescribed engine failures
must be substantiated by test or other
data applicable to the particular engine-propeller combination.
(4) The timing and magnitude of the
probable pilot corrective action must
be conservatively estimated, considering the characteristics of the particular engine-propeller-airplane combination.
(b) Pilot corrective action may be assumed to be initiated at the time maximum yawing velocity is reached, but
not earlier than two seconds after the
engine failure. The magnitude of the
corrective action may be based on the
control forces specified in Section 25.397(b) except that lower forces may be assumed
where it is shown by anaylsis or test
that these forces can control the yaw
and roll resulting from the prescribed
engine failure conditions.

Section 25.371

Gyroscopic loads.

The structure supporting any engine
or auxiliary power unit must be designed for the loads, including gyroscopic loads, arising from the conditions specified in SectionSection 25.331, 25.341, 25.349,
25.351, 25.473, 25.479, and 25.481, with the
engine or auxiliary power unit at the
maximum rotating speed appropriate
to the condition. For the purposes of
compliance with this paragraph, the
pitch maneuver in Section 25.331(c)(1) must be
carried out until the positive limit maneuvering load factor (point A2 in
Section 25.333(b)) is reached.
[Amdt. 25-141, 79 FR 73468, Dec. 11, 2014]

Section 25.373

Speed control devices.

If speed control devices (such as
spoilers and drag flaps) are installed
for use in en route conditions - 
(a) The airplane must be designed for
the symmetrical maneuvers prescribed
in SectionSection 25.333 and 25.337, the yawing maneuvers in Section 25.351, and the vertical and
lateral gust and turbulence conditions
prescribed in Section 25.341(a) and (b) at each
setting and the maximum speed associated with that setting; and
(b) If the device has automatic operating or load limiting features, the airplane must be designed for the maneuver and gust conditions prescribed in
paragraph (a) of this section, at the
speeds and corresponding device positions that the mechanism allows.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-72, 55 FR 29776, July 20,
1990; Amdt. 25-86, 61 FR 5222, Feb. 9, 1996;
Amdt. 25-141, 79 FR 73468, Dec. 11, 2014]

CONTROL SURFACE AND SYSTEM LOADS
Section 25.391 Control surface loads: General.
The control surfaces must be designed for the limit loads resulting
from the flight conditions in SectionSection 25.331,
25.341(a) and (b), 25.349, and 25.351, considering the requirements for - 
(a) Loads parallel to hinge line, in
Section 25.393;
(b) Pilot effort effects, in Section 25.397;
(c) Trim tab effects, in Section 25.407;
(d) Unsymmetrical loads, in Section 25.427;
and

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