Federal Aviation Administration, DOT

Section 25.253

(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 gravity position, relevant to each operating
condition, within the range of loading
conditions for which certification is requested.
(c) In the water conditions of paragraph (b) of this section, and in the
corresponding wind conditions, the seaplane or amphibian must be able to
drift for five minutes with engines inoperative, aided, if necessary, by a sea
anchor.
MISCELLANEOUS FLIGHT REQUIREMENTS

spaschal on DSK3GDR082PROD with CFR

Section 25.251

Vibration and buffeting.

(a) The airplane must be demonstrated in flight to be free from any
vibration and buffeting that would prevent 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 appropriate speed and power conditions up to
VDF/MDF. The maximum speeds shown
must be used in establishing the operating limitations of the airplane in accordance with Section 25.1505.
(c) Except as provided in paragraph
(d) of this section, there may be no buffeting condition, in normal flight, including configuration changes during
cruise, severe enough to interfere with
the control of the airplane, to cause excessive fatigue to the crew, or to cause
structural damage. Stall warning buffeting within these limits is allowable.
(d) There may be no perceptible buffeting condition in the cruise configuration in straight flight at any speed
up to VMO/MMO, except that stall warning buffeting is allowable.
(e) For an airplane with MD 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 buffeting 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, altitude, and weight must provide a suffi-

cient range of speeds and load factors
for normal operations. Probable inadvertent excursions beyond the boundaries 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]

Section 25.253 High-speed characteristics.
(a) Speed increase and recovery characteristics. The following speed increase
and recovery characteristics must be
met:
(1) Operating conditions and characteristics 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 VMO/MMO. These conditions and characteristics include gust
upsets, inadvertent control movements, low stick force gradient in relation to control friction, passenger
movement, leveling off from climb, and
descent from Mach to airspeed limit altitudes.
(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 VMO/MMO, without - 
(i) Exceptional piloting strength or
skill;
(ii) Exceeding VD/MD, VDF/MDF, 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 VMO/MMO, there must be no
reversal of the response to control
input about any axis at any speed up to
VDF/MDF. Any tendency to pitch, roll, or
yaw must be mild and readily controllable, using normal piloting techniques. When the airplane is trimmed
at VMO/MMO, the slope of the elevator
control force versus speed curve need
not be stable at speeds greater than
VFC/MFC, but there must be a push force
at all speeds up to VDF/MDF and there
must be no sudden or excessive reduction of elevator control force as VDF/
MDF is reached.
(4) Adequate roll capability to assure
a prompt recovery from a lateral upset

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