229
Federal Aviation Administration, DOT
§ 25.239
reasonably expected operating condi-
tion or when rebound occurs during
landing or takeoff. In addition—
(1) Wheel brakes must operate
smoothly and may not cause any undue
tendency to nose over; and
(2) If a tail-wheel landing gear is
used, it must be possible, during the
takeoff ground run on concrete, to
maintain any attitude up to thrust line
level, at 75 percent of
V
SR1
.
(b) For seaplanes and amphibians,
the most adverse water conditions safe
for takeoff, taxiing, and landing, must
be established.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–108, 67 FR 70828, Nov.
26, 2002]
§ 25.233
Directional stability and con-
trol.
(a) There may be no uncontrollable
ground-looping tendency in 90
°
cross
winds, up to a wind velocity of 20 knots
or 0.2
V
SR0
, whichever is greater, except
that the wind velocity need not exceed
25 knots at any speed at which the air-
plane may be expected to be operated
on the ground. This may be shown
while establishing the 90
°
cross compo-
nent of wind velocity required by
§ 25.237.
(b) Landplanes must be satisfactorily
controllable, without exceptional pilot-
ing skill or alertness, in power-off land-
ings at normal landing speed, without
using brakes or engine power to main-
tain a straight path. This may be
shown during power-off landings made
in conjunction with other tests.
(c) The airplane must have adequate
directional control during taxiing. This
may be shown during taxiing prior to
takeoffs made in conjunction with
other tests.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–23, 35 FR 5671, Apr. 8,
1970; Amdt. 25–42, 43 FR 2322, Jan. 16, 1978;
Amdt. 25–94, 63 FR 8848, Feb. 23, 1998; Amdt.
25–108, 67 FR 70828, Nov. 26, 2002]
§ 25.235
Taxiing condition.
The shock absorbing mechanism may
not damage the structure of the air-
plane when the airplane is taxied on
the roughest ground that may reason-
ably be expected in normal operation.
§ 25.237
Wind velocities.
(a) For land planes and amphibians,
the following applies:
(1) A 90-degree cross component of
wind velocity, demonstrated to be safe
for takeoff and landing, must be estab-
lished for dry runways and must be at
least 20 knots or 0.2 V
SR0
, whichever is
greater, except that it need not exceed
25 knots.
(2) The crosswind component for
takeoff established without ice accre-
tions is valid in icing conditions.
(3) The landing crosswind component
must be established for:
(i) Non-icing conditions, and
(ii) Icing conditions with the most
critical of the landing ice accretion(s)
defined in Appendices C and O of this
part, as applicable, in accordance with
§ 25.21(g).
(b) For seaplanes and amphibians,
the following applies:
(1) A 90-degree cross component of
wind velocity, up to which takeoff and
landing is safe under all water condi-
tions that may reasonably be expected
in normal operation, must be estab-
lished and must be at least 20 knots or
0.2 V
SR0
, whichever is greater, except
that it need not exceed 25 knots.
(2) A wind velocity, for which taxiing
is safe in any direction under all water
conditions that may reasonably be ex-
pected in normal operation, must be es-
tablished and must be at least 20 knots
or 0.2 V
SR0
, whichever is greater, except
that it need not exceed 25 knots.
[Amdt. 25–42, 43 FR 2322, Jan. 16, 1978, as
amended by Amdt. 25–108, 67 FR 70827, Nov.
26, 2002; Amdt. 25–121, 72 FR 44668, Aug. 8,
2007; Amdt. 25–140, 79 FR 65525, Nov. 4, 2014]
§ 25.239
Spray characteristics, control,
and stability on water.
(a) For seaplanes and amphibians,
during takeoff, taxiing, and landing,
and in the conditions set forth in para-
graph (b) of this section, there may be
no—
(1) Spray characteristics that would
impair the pilot’s view, cause damage,
or result in the taking in of an undue
quantity of water;
(2) Dangerously uncontrollable
porpoising, bounding, or swinging tend-
ency; or
(3) Immersion of auxiliary floats or
sponsons, wing tips, propeller blades,
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14 CFR Ch. I (1–1–24 Edition)
§ 25.251
or other parts not designed to with-
stand the resulting water loads.
(b) Compliance with the require-
ments of paragraph (a) of this section
must be shown—
(1) In water conditions, from smooth
to the most adverse condition estab-
lished in accordance with § 25.231;
(2) In wind and cross-wind velocities,
water currents, and associated waves
and swells that may reasonably be ex-
pected in operation on water;
(3) At speeds that may reasonably be
expected in operation on water;
(4) With sudden failure of the critical
engine at any time while on water; and
(5) At each weight and center of grav-
ity position, relevant to each operating
condition, within the range of loading
conditions for which certification is re-
quested.
(c) In the water conditions of para-
graph (b) of this section, and in the
corresponding wind conditions, the sea-
plane or amphibian must be able to
drift for five minutes with engines in-
operative, aided, if necessary, by a sea
anchor.
M
ISCELLANEOUS
F
LIGHT
R
EQUIREMENTS
§ 25.251
Vibration and buffeting.
(a) The airplane must be dem-
onstrated in flight to be free from any
vibration and buffeting that would pre-
vent continued safe flight in any likely
operating condition.
(b) Each part of the airplane must be
demonstrated in flight to be free from
excessive vibration under any appro-
priate speed and power conditions up to
V
DF
/M
DF
. The maximum speeds shown
must be used in establishing the oper-
ating limitations of the airplane in ac-
cordance with § 25.1505.
(c) Except as provided in paragraph
(d) of this section, there may be no buf-
feting condition, in normal flight, in-
cluding configuration changes during
cruise, severe enough to interfere with
the control of the airplane, to cause ex-
cessive fatigue to the crew, or to cause
structural damage. Stall warning buf-
feting within these limits is allowable.
(d) There may be no perceptible buf-
feting condition in the cruise configu-
ration in straight flight at any speed
up to
V
MO
/
M
MO,
except that stall warn-
ing buffeting is allowable.
(e) For an airplane with M
D
greater
than .6 or with a maximum operating
altitude greater than 25,000 feet, the
positive maneuvering load factors at
which the onset of perceptible buf-
feting occurs must be determined with
the airplane in the cruise configuration
for the ranges of airspeed or Mach
number, weight, and altitude for which
the airplane is to be certificated. The
envelopes of load factor, speed, alti-
tude, and weight must provide a suffi-
cient range of speeds and load factors
for normal operations. Probable inad-
vertent excursions beyond the bound-
aries of the buffet onset envelopes may
not result in unsafe conditions.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–23, 35 FR 5671, Apr. 8,
1970; Amdt. 25–72, 55 FR 29775, July 20, 1990;
Amdt. 25–77, 57 FR 28949, June 29, 1992]
§ 25.253
High-speed characteristics.
(a)
Speed increase and recovery charac-
teristics. The following speed increase
and recovery characteristics must be
met:
(1) Operating conditions and charac-
teristics likely to cause inadvertent
speed increases (including upsets in
pitch and roll) must be simulated with
the airplane trimmed at any likely
cruise speed up to
V
MO
/
M
MO
. These con-
ditions and characteristics include gust
upsets, inadvertent control move-
ments, low stick force gradient in rela-
tion to control friction, passenger
movement, leveling off from climb, and
descent from Mach to airspeed limit al-
titudes.
(2) Allowing for pilot reaction time
after effective inherent or artificial
speed warning occurs, it must be shown
that the airplane can be recovered to a
normal attitude and its speed reduced
to
V
MO
/
M
MO,
without—
(i) Exceptional piloting strength or
skill;
(ii) Exceeding
V
D
/
M
D,
V
DF
/
M
DF,
or the
structural limitations; and
(iii) Buffeting that would impair the
pilot’s ability to read the instruments
or control the airplane for recovery.
(3) With the airplane trimmed at any
speed up to V
MO
/M
MO
, there must be no
reversal of the response to control
input about any axis at any speed up to
V
DF
/M
DF
. Any tendency to pitch, roll, or
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