Federal Aviation Administration, DOT

Section 25.201

stable sense. This factor of proportionality must lie between limits found
necessary for safe operation. The range
of sideslip angles evaluated must include those sideslip angles resulting
from the lesser of:
(1) One-half of the available rudder
control input; and
(2) A rudder control force of 180
pounds.
(d) For sideslip angles greater than
those prescribed by paragraph (c) of
this section, up to the angle at which
full rudder control is used or a rudder
control force of 180 pounds is obtained,
the rudder control forces may not reverse, and increased rudder deflection
must be needed for increased angles of
sideslip. Compliance with this requirement must be shown using straight,
steady sideslips, unless full lateral control input is achieved before reaching
either full rudder control input or a
rudder control force of 180 pounds; a
straight, steady sideslip need not be
maintained after achieving full lateral
control input. This requirement must
be met at all approved landing gear and
flap positions for the range of operating speeds and power conditions appropriate to each landing gear and flap
position with all engines operating.
[Amdt. 25-135, 76 FR 74654, Dec. 1, 2011]

Section 25.181

Dynamic stability.

spaschal on DSK3GDR082PROD with CFR

(a) Any short period oscillation, not
including combined lateral-directional
oscillations, occurring between 1.13 VSR
and maximum allowable speed appropriate to the configuration of the airplane must be heavily damped with the
primary controls - 
(1) Free; and
(2) In a fixed position.
(b) Any combined lateral-directional
oscillations ( - Dutch roll - ) occurring
between 1.13 VSR and maximum allowable speed appropriate to the configuration of the airplane must be positively damped with controls free, and
must be controllable with normal use
of the primary controls without requiring exceptional pilot skill.
[Amdt. 25-42, 43 FR 2322, Jan. 16, 1978, as
amended by Amdt. 25-72, 55 FR 29775, July 20,
1990; 55 FR 37607, Sept. 12, 1990; Amdt. 25-108,
67 FR 70827, Nov. 26, 2002]

STALLS
Section 25.201

Stall demonstration.

(a) Stalls must be shown in straight
flight and in 30 degree banked turns
with - 
(1) Power off; and
(2) The power necessary to maintain
level flight at 1.5 VSR1 (where VSR1 corresponds to the reference stall speed at
maximum landing weight with flaps in
the approach position and the landing
gear retracted).
(b) In each condition required by
paragraph (a) of this section, it must
be possible to meet the applicable requirements of Section 25.203 with - 
(1) Flaps, landing gear, and deceleration devices in any likely combination
of positions approved for operation;
(2) Representative weights within the
range for which certification is requested;
(3) The most adverse center of gravity for recovery; and
(4) The airplane trimmed for straight
flight at the speed prescribed in
Section 25.103(b)(6).
(c) The following procedures must be
used to show compliance with Section 25.203;
(1) Starting at a speed sufficiently
above the stalling speed to ensure that
a steady rate of speed reduction can be
established, apply the longitudinal
control so that the speed reduction
does not exceed one knot per second
until the airplane is stalled.
(2) In addition, for turning flight
stalls, apply the longitudinal control
to achieve airspeed deceleration rates
up to 3 knots per second.
(3) As soon as the airplane is stalled,
recover by normal recovery techniques.
(d) The airplane is considered stalled
when the behavior of the airplane gives
the pilot a clear and distinctive indication of an acceptable nature that the
airplane is stalled. Acceptable indications of a stall, occurring either individually or in combination, are - 
(1) A nose-down pitch that cannot be
readily arrested;
(2) Buffeting, of a magnitude and severity that is a strong and effective deterrent to further speed reduction; or
(3) The pitch control reaches the aft
stop and no further increase in pitch
attitude occurs when the control is

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