501 

Federal Aviation Administration, DOT 

§ 27.427 

the system allows the pilot to apply, 
but not less than 0.60 times the forces 
specified in § 27.397. 

(b) Each primary control system, in-

cluding its supporting structure, must 
be designed as follows: 

(1) The system must withstand loads 

resulting from the limit pilot forces 
prescribed in § 27.397. 

(2) Notwithstanding paragraph (b)(3) 

of this section, when power-operated 
actuator controls or power boost con-
trols are used, the system must also 
withstand the loads resulting from the 
force output of each normally ener-
gized power device, including any sin-
gle power boost or actuator system 
failure. 

(3) If the system design or the normal 

operating loads are such that a part of 
the system cannot react to the limit 
pilot forces prescribed in § 27.397, that 
part of the system must be designed to 
withstand the maximum loads that can 
be obtained in normal operation. The 
minimum design loads must, in any 
case, provide a rugged system for serv-
ice use, including consideration of fa-
tigue, jamming, ground gusts, control 
inertia, and friction loads. In the ab-
sence of rational analysis, the design 
loads resulting from 0.60 of the speci-
fied limit pilot forces are acceptable 
minimum design loads. 

(4) If operational loads may be ex-

ceeded through jamming, ground gusts, 
control inertia, or friction, the system 
must withstand the limit pilot forces 
specified in § 27.397, without yielding. 

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as 
amended by Amdt. 27–26, 55 FR 7999, Mar. 6, 
1990] 

§ 27.397

Limit pilot forces and torques. 

(a) Except as provided in paragraph 

(b) of this section, the limit pilot 
forces are as follows: 

(1) For foot controls, 130 pounds. 
(2) For stick controls, 100 pounds fore 

and aft, and 67 pounds laterally. 

(b) For flap, tab, stabilizer, rotor 

brake, and landing gear operating con-
trols, the follows apply (R = radius in 
inches): 

(1) Crank, wheel, and lever controls, 

[1 + R]/3 

× 

50 pounds, but not less than 

50 pounds nor more than 100 pounds for 
hand operated controls or 130 pounds 
for foot operated controls, applied at 

any angle within 20 degrees of the 
plane of motion of the control. 

(2) Twist controls, 80R inch-pounds. 

[Amdt. 27–11, 41 FR 55469, Dec. 20, 1976, as 
amended by Amdt. 27–40, 66 FR 23538, May 9, 
2001] 

§ 27.399

Dual control system. 

Each dual primary flight control sys-

tem must be designed to withstand the 
loads that result when pilot forces of 
0.75 times those obtained under § 27.395 
are applied— 

(a) In opposition; and 
(b) In the same direction. 

§ 27.411

Ground clearance: tail rotor 

guard. 

(a) It must be impossible for the tail 

rotor to contact the landing surface 
during a normal landing. 

(b) If a tail rotor guard is required to 

show compliance with paragraph (a) of 
this section— 

(1) Suitable design loads must be es-

tablished for the guard; and 

(2) The guard and its supporting 

structure must be designed to with-
stand those loads. 

§ 27.427

Unsymmetrical loads. 

(a) Horizontal tail surfaces and their 

supporting structure must be designed 
for unsymmetrical loads arising from 
yawing and rotor wake effects in com-
bination with the prescribed flight con-
ditions. 

(b) To meet the design criteria of 

paragraph (a) of this section, in the ab-
sence of more rational data, both of the 
following must be met: 

(1) One hundred percent of the max-

imum loading from the symmetrical 
flight conditions acts on the surface on 
one side of the plane of symmetry, and 
no loading acts on the other side. 

(2) Fifty percent of the maximum 

loading from the symmetrical flight 
conditions acts on the surface on each 
side of the plane of symmetry but in 
opposite directions. 

(c) For empennage arrangements 

where the horizontal tail surfaces are 
supported by the vertical tail surfaces, 
the vertical tail surfaces and sup-
porting structure must be designed for 
the combined vertical and horizontal 
surface loads resulting from each pre-
scribed flight condition, considered 

VerDate Sep<11>2014 

09:06 Jun 28, 2024

Jkt 262046

PO 00000

Frm 00511

Fmt 8010

Sfmt 8010

Y:\SGML\262046.XXX

262046

jspears on DSK121TN23PROD with CFR