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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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230 

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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