[Code of Federal Regulations]
[Title 14, Volume 1]
[Revised as of January 1, 2003]
From the U.S. Government Printing Office via GPO Access
[CITE: 14CFR27.33]

[Page 538]
 
                     TITLE 14--AERONAUTICS AND SPACE
 
CHAPTER I--FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION
 
PART 27--AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT--Table of Contents
 
                            Subpart B--Flight
 
Sec. 27.33  Main rotor speed and pitch limits.

    (a) Main rotor speed limits. A range of main rotor speeds must be 
established that--
    (1) With power on, provides adequate margin to accommodate the 
variations in rotor speed occurring in any appropriate maneuver, and is 
consistent with the kind of governor or synchronizer used; and
    (2) With power off, allows each appropriate autorotative maneuver to 
be performed throughout the ranges of airspeed and weight for which 
certification is requested.
    (b) Normal main rotor high pitch limits (power on). For rotocraft, 
except helicopters required to have a main rotor low speed warning under 
paragraph (e) of this section. It must be shown, with power on and 
without exceeding approved engine maximum limitations, that main rotor 
speeds substantially less than the minimum approved main rotor speed 
will not occur under any sustained flight condition. This must be met 
by--
    (1) Appropriate setting of the main rotor high pitch stop;
    (2) Inherent rotorcraft characteristics that make unsafe low main 
rotor speeds unlikely; or
    (3) Adequate means to warn the pilot of unsafe main rotor speeds.
    (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 overspeeding of the rotor without 
exceptional 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 inadvertently, additional pitch may be made available for 
emergency use.
    (e) Main rotor low speed warning for helicopters. For each single 
engine helicopter, and each multiengine helicopter 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, including power-on and power-off flight, when the speed of a 
main rotor approaches a value that can jeopardize safe flight.
    (2) The warning may be furnished either through the inherent 
aerodynamic qualities of the helicopter or by a device.
    (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 device must automatically 
deactivate and reset when the low-speed condition is corrected. If the 
device has an audible 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 Federal 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]

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