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14 CFR Ch. I (1–1–24 Edition)
§ 25.21
Subpart B—Flight
G
ENERAL
§ 25.21
Proof of compliance.
(a) Each requirement of this subpart
must be met at each appropriate com-
bination of weight and center of grav-
ity within the range of loading condi-
tions for which certification is re-
quested. This must be shown—
(1) By tests upon an airplane of the
type for which certification is re-
quested, or by calculations based on,
and equal in accuracy to, the results of
testing; and
(2) By systematic investigation of
each probable combination of weight
and center of gravity, if compliance
cannot be reasonably inferred from
combinations investigated.
(b) [Reserved]
(c) The controllability, stability,
trim, and stalling characteristics of
the airplane must be shown for each al-
titude up to the maximum expected in
operation.
(d) Parameters critical for the test
being conducted, such as weight, load-
ing (center of gravity and inertia), air-
speed, power, and wind, must be main-
tained within acceptable tolerances of
the critical values during flight test-
ing.
(e) If compliance with the flight
characteristics requirements is depend-
ent upon a stability augmentation sys-
tem or upon any other automatic or
power-operated system, compliance
must be shown with §§ 25.671 and 25.672.
(f) In meeting the requirements of
§§ 25.105(d), 25.125, 25.233, and 25.237, the
wind velocity must be measured at a
height of 10 meters above the surface,
or corrected for the difference between
the height at which the wind velocity
is measured and the 10-meter height.
(g) The requirements of this subpart
associated with icing conditions apply
only if the applicant is seeking certifi-
cation for flight in icing conditions.
(1) Paragraphs (g)(3) and (4) of this
section apply only to airplanes with
one or both of the following attributes:
(i) Maximum takeoff gross weight is
less than 60,000 lbs; or
(ii) The airplane is equipped with re-
versible flight controls.
(2) Each requirement of this subpart,
except §§ 25.121(a), 25.123(c), 25.143(b)(1)
and (2), 25.149, 25.201(c)(2), 25.239, and
25.251(b) through (e), must be met in
the icing conditions specified in Appen-
dix C of this part. Section 25.207(c) and
(d) must be met in the landing configu-
ration in the icing conditions specified
in Appendix C, but need not be met for
other configurations. Compliance must
be shown using the ice accretions de-
fined in part II of Appendix C of this
part, assuming normal operation of the
airplane and its ice protection system
in accordance with the operating limi-
tations and operating procedures estab-
lished by the applicant and provided in
the airplane flight manual.
(3) If the applicant does not seek cer-
tification for flight in all icing condi-
tions defined in Appendix O of this
part, each requirement of this subpart,
except §§ 25.105, 25.107, 25.109, 25.111,
25.113, 25.115, 25.121, 25.123, 25.143(b)(1),
(b)(2), and (c)(1), 25.149, 25.201(c)(2),
25.207(c), (d), and (e)(1), 25.239, and
25.251(b) through (e), must be met in
the Appendix O icing conditions for
which certification is not sought in
order to allow a safe exit from those
conditions. Compliance must be shown
using the ice accretions defined in part
II, paragraphs (b) and (d) of Appendix
O, assuming normal operation of the
airplane and its ice protection system
in accordance with the operating limi-
tations and operating procedures estab-
lished by the applicant and provided in
the airplane flight manual.
(4) If the applicant seeks certifi-
cation for flight in any portion of the
icing conditions of Appendix O of this
part, each requirement of this subpart,
except §§ 25.121(a), 25.123(c), 25.143(b)(1)
and (2), 25.149, 25.201(c)(2), 25.239, and
25.251(b) through (e), must be met in
the Appendix O icing conditions for
which certification is sought. Section
25.207(c) and (d) must be met in the
landing configuration in the Appendix
O icing conditions for which certifi-
cation is sought, but need not be met
for other configurations. Compliance
must be shown using the ice accretions
defined in part II, paragraphs (c) and
(d) of Appendix O, assuming normal op-
eration of the airplane and its ice pro-
tection system in accordance with the
operating limitations and operating
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