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14 CFR Ch. I (1–1–19 Edition)

§ 25.147

§ 25.147

Directional and lateral con-

trol.

(a)

Directional control; general.

It must

be possible, with the wings level, to
yaw into the operative engine and to
safely make a reasonably sudden
change in heading of up to 15 degrees in
the direction of the critical inoperative
engine. This must be shown at 1.3 V

for heading changes up to 15 degrees
(except that the heading change at
which the rudder pedal force is 150
pounds need not be exceeded), and
with—

(1) The critical engine inoperative

and its propeller in the minimum drag
position;

(2) The power required for level flight

at 1.3

R1, but not more than max-

imum continuous power;

(3) The most unfavorable center of

gravity;

(4) Landing gear retracted;
(5) Flaps in the approach position;

and

(6) Maximum landing weight.
(b)

Directional control; airplanes with

four or more engines.

Airplanes with

four or more engines must meet the re-
quirements of paragraph (a) of this sec-
tion except that—

(1) The two critical engines must be

inoperative with their propellers (if ap-
plicable) in the minimum drag posi-
tion;

(2) [Reserved]
(3) The flaps must be in the most fa-

vorable climb position.

(c)

Lateral control; general.

It must be

possible to make 20

banked turns, with

and against the inoperative engine,
from steady flight at a speed equal to
1.3

R1, with—

(1) The critical engine inoperative

and its propeller (if applicable) in the
minimum drag position;

(2) The remaining engines at max-

imum continuous power;

(3) The most unfavorable center of

gravity;

(4) Landing gear (i) retracted and (ii)

extended;

(5) Flaps in the most favorable climb

position; and

(6) Maximum takeoff weight.
(d)

Lateral control; roll capability.

With

the critical engine inoperative, roll re-
sponse must allow normal maneuvers.
Lateral control must be sufficient, at

the speeds likely to be used with one
engine inoperative, to provide a roll
rate necessary for safety without ex-
cessive control forces or travel.

(e)

Lateral control; airplanes with four

or more engines.

Airplanes with four or

more engines must be able to make 20

banked turns, with and against the in-
operative engines, from steady flight at
a speed equal to 1.3

R1, with max-

imum continuous power, and with the
airplane in the configuration pre-
scribed by paragraph (b) of this section.

(f)

Lateral control; all engines oper-

ating.

With the engines operating, roll

response must allow normal maneuvers
(such as recovery from upsets produced
by gusts and the initiation of evasive
maneuvers). There must be enough ex-
cess lateral control in sideslips (up to
sideslip angles that might be required
in normal operation), to allow a lim-
ited amount of maneuvering and to
correct for gusts. Lateral control must
be enough at any speed up to

to provide a peak roll rate necessary
for safety, without excessive control
forces or travel.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–42, 43 FR 2321, Jan. 16,
1978; Amdt. 25–72, 55 FR 29774, July 20, 1990;
Amdt. 25–108, 67 FR 70827, Nov. 26, 2002;
Amdt. 25–115, 69 FR 40527, July 2, 2004]

§ 25.149

Minimum control speed.

(a) In establishing the minimum con-

trol speeds required by this section, the
method used to simulate critical en-
gine failure must represent the most
critical mode of powerplant failure
with respect to controllability ex-
pected in service.

(b) V

is the calibrated airspeed at

which, when the critical engine is sud-
denly made inoperative, it is possible
to maintain control of the airplane
with that engine still inoperative and
maintain straight flight with an angle
of bank of not more than 5 degrees.

(c)

may not exceed 1.13

with—

(1) Maximum available takeoff power

or thrust on the engines;

(2) The most unfavorable center of

gravity;

(3) The airplane trimmed for takeoff;
(4) The maximum sea level takeoff

weight (or any lesser weight necessary
to show

);

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