641 

Federal Aviation Administration, DOT 

§ 27.49 

(c) 

Normal main rotor low pitch limits 

(power off). It must be shown, with 
power off, that— 

(1) The normal main rotor low pitch 

limit provides sufficient rotor speed, in 
any autorotative condition, under the 
most critical combinations of weight 
and airspeed; and 

(2) It is possible to prevent over-

speeding of the rotor without excep-
tional piloting skill. 

(d) 

Emergency high pitch. If the main 

rotor high pitch stop is set to meet 
paragraph (b)(1) of this section, and if 
that stop cannot be exceeded inadvert-
ently, additional pitch may be made 
available for emergency use. 

(e) 

Main rotor low speed warning for 

helicopters. For each single engine heli-
copter, and each multiengine heli-
copter that does not have an approved 
device that automatically increases 
power on the operating engines when 
one engine fails, there must be a main 
rotor low speed warning which meets 
the following requirements: 

(1) The warning must be furnished to 

the pilot in all flight conditions, in-
cluding power-on and power-off flight, 
when the speed of a main rotor ap-
proaches a value that can jeopardize 
safe flight. 

(2) The warning may be furnished ei-

ther through the inherent aerodynamic 
qualities of the helicopter or by a de-
vice. 

(3) The warning must be clear and 

distinct under all conditons, and must 
be clearly distinguishable from all 
other warnings. A visual device that 
requires the attention of the crew 
within the cockpit is not acceptable by 
itself. 

(4) If a warning device is used, the de-

vice must automatically deactivate 
and reset when the low-speed condition 
is corrected. If the device has an audi-
ble warning, it must also be equipped 
with a means for the pilot to manually 
silence the audible warning before the 
low-speed condition is corrected. 

(Secs. 313(a), 601, 603, 604, and 605 of the Fed-
eral Aviation Act of 1958 (49 U.S.C. 1354(a), 
1421, 1423, 1424, and 1425); and sec. 6(c) of the 
Dept. of Transportation Act (49 U.S.C. 
1655(c))) 

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as 
amended by Amdt. 27–2, 33 FR 962, Jan. 26, 
1968; Amdt. 27–14, 43 FR 2324, Jan. 16, 1978] 

P

ERFORMANCE

 

§ 27.45

General. 

(a) Unless otherwise prescribed, the 

performance requirements of this sub-
part must be met for still air and a 
standard atmosphere. 

(b) The performance must correspond 

to the engine power available under the 
particular ambient atmospheric condi-
tions, the particular flight condition, 
and the relative humidity specified in 
paragraphs (d) or (e) of this section, as 
appropriate. 

(c) The available power must cor-

respond to engine power, not exceeding 
the approved power, less— 

(1) Installation losses; and 
(2) The power absorbed by the acces-

sories and services appropriate to the 
particular ambient atmopheric condi-
tions and the particular flight condi-
tion. 

(d) For reciprocating engine-powered 

rotorcraft, the performance, as affected 
by engine power, must be based on a 
relative humidity of 80 percent in a 
standard atmosphere. 

(e) For turbine engine-powered rotor-

craft, the performance, as affected by 
engine power, must be based on a rel-
ative humidity of— 

(1) 80 percent, at and below standard 

temperature; and 

(2) 34 percent, at and above standard 

temperature plus 50 degrees F. Between 
these two temperatures, the relative 
humidity must vary linearly. 

(f) For turbine-engine-powered rotor-

craft, a means must be provided to per-
mit the pilot to determine prior to 
takeoff that each engine is capable of 
developing the power necessary to 
achieve the applicable rotorcraft per-
formance prescribed in this subpart. 

(Secs. 313(a), 601, 603, 604, and 605 of the Fed-
eral Aviation Act of 1958 (49 U.S.C. 1354(a), 
1421, 1423, 1424, and 1425); and sec. 6(c) of the 
Dept. of Transportation Act (49 U.S.C. 
1655(c))) 

[Amdt. 27–14, 43 FR 2324, Jan. 16, 1978, as 
amended by Amdt. 27–21, 49 FR 44432, Nov. 6, 
1984] 

§ 27.49

Performance at minimum oper-

ating speed. 

(a) For helicopters— 

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