Appendix B to Part 27 - Airworthiness Criteria for Helicopter Instrument Flight
14:1.0.1.3.14.9.201.1.22 : Appendix B
Appendix B to Part 27 - Airworthiness Criteria for Helicopter
Instrument Flight
I. General. A normal category helicopter may not be type
certificated for operation under the instrument flight rules (IFR)
of this chapter unless it meets the design and installation
requirements contained in this appendix.
II. Definitions. (a) VYI means instrument climb speed,
utilized instead of VY for compliance with the climb requirements
for instrument flight.
(b) VNEI means instrument flight never exceed speed, utilized
instead of VNE for compliance with maximum limit speed requirements
for instrument flight.
(c) VMINI means instrument flight minimum speed, utilized in
complying with minimum limit speed requirements for instrument
flight.
III. Trim. It must be possible to trim the cyclic,
collective, and directional control forces to zero at all approved
IFR airspeeds, power settings, and configurations appropriate to
the type.
IV. Static longitudinal stability. (a) General.
The helicopter must possess positive static longitudinal control
force stability at critical combinations of weight and center of
gravity at the conditions specified in paragraph IV (b) or (c) of
this appendix, as appropriate. The stick force must vary with speed
so that any substantial speed change results in a stick force
clearly perceptible to the pilot. For single-pilot approval, the
airspeed must return to within 10 percent of the trim speed when
the control force is slowly released for each trim condition
specified in paragraph IV(b) of the this appendix.
(b) For single-pilot approval:
(1) Climb. Stability must be shown in climb throughout
the speed range 20 knots either side of trim with -
(i) The helicopter trimmed at VYI;
(ii) Landing gear retracted (if retractable); and
(iii) Power required for limit climb rate (at least 1,000 fpm)
at VYI or maximum continuous power, whichever is less.
(2) Cruise. Stability must be shown throughout the speed
range from 0.7 to 1.1 VH or VNEI, whichever is lower, not to exceed
±20 knots from trim with -
(i) The helicopter trimmed and power adjusted for level flight
at 0.9 VH or 0.9 VNEI, whichever is lower; and
(ii) Landing gear retracted (if retractable).
(3) Slow cruise. Stability must be shown throughout the
speed range from 0.9 VMINI to 1.3 VMINI or 20 knots above trim
speed, whichever is greater, with -
(i) the helicopter trimmed and power adjusted for level flight
at 1.1 VMINI; and
(ii) Landing gear retracted (if retractable).
(4) Descent. Stability must be shown throughout the speed
range 20 knots either side of trim with -
(i) The helicopter trimmed at 0.8 VH or 0.8 VNEI (or 0.8 VLE for
the landing gear extended case), whichever is lower;
(ii) Power required for 1,000 fpm descent at trim speed; and
(iii) Landing gear extended and retracted, if applicable.
(5) Approach. Stability must be shown throughout the
speed range from 0.7 times the minimum recommended approach speed
to 20 knots above the maximum recommended approach speed with -
(i) The helicopter trimmed at the recommended approach speed or
speeds;
(ii) Landing gear extended and retracted, if applicable; and
(iii) Power required to maintain a 3° glide path and power
required to maintain the steepest approach gradient for which
approval is requested.
(c) Helicopters approved for a minimum crew of two pilots must
comply with the provisions of paragraphs IV(b)(2) and IV(b)(5) of
this appendix.
V. Static Lateral Directional Stability. (a) Static
directional stability must be positive throughout the approved
ranges of airspeed, power, and vertical speed. In straight and
steady sideslips up to ±10° from trim, directional control position
must increase without discontinuity with the angle of sideslip,
except for a small range of sideslip angles around trim. At greater
angles up to the maximum sideslip angle appropriate to the type,
increased directional control position must produce an increased
angle of sideslip. It must be possible to maintain balanced flight
without exceptional pilot skill or alertness.
(b) During sideslips up to ±10° from trim throughout the
approved ranges of airspeed, power, and vertical speed, there must
be no negative dihedral stability perceptible to the pilot through
lateral control motion or force. Longitudinal cyclic movement with
sideslip must not be excessive.
VI. Dynamic stability. (a) For single-pilot approval
-
(1) Any oscillation having a period of less than 5 seconds must
damp to 1/2 amplitude in not more than one cycle.
(2) Any oscillation having a period of 5 seconds or more but
less than 10 seconds must damp to 1/2 amplitude in not more than
two cycles.
(3) Any oscillation having a period of 10 seconds or more but
less than 20 seconds must be damped.
(4) Any oscillation having a period of 20 seconds or more may
not achieve double amplitude in less than 20 seconds.
(5) Any aperiodic response may not achieve double amplitude in
less than 6 seconds.
(b) For helicopters approved with a minimum crew of two pilots
-
(1) Any oscillation having a period of less than 5 seconds must
damp to 1/2 amplitude in not more than two cycles.
(2) Any oscillation having a period of 5 seconds or more but
less than 10 seconds must be damped.
(3) Any oscillation having a period of 10 seconds or more may
not achieve double amplitude in less than 10 seconds.
VII. Stability Augmentation System (SAS).
(a) If a SAS is used, the reliability of the SAS must be related
to the effects of its failure. Any SAS failure condition that would
prevent continued safe flight and landing must be extremely
improbable. It must be shown that, for any failure condition of the
SAS that is not shown to be extremely improbable -
(1) The helicopter is safely controllable when the failure or
malfunction occurs at any speed or altitude within the approved IFR
operating limitations; and
(2) The overall flight characteristics of the helicopter allow
for prolonged instrument flight without undue pilot effort.
Additional unrelated probable failures affecting the control system
must be considered. In addition -
(i) The controllability and maneuverability requirements in
Subpart B of this part must be met throughout a practical flight
envelope;
(ii) The flight control, trim, and dynamic stability
characteristics must not be impaired below a level needed to allow
continued safe flight and landing; and
(iii) The static longitudinal and static directional stability
requirements of Subpart B must be met throughout a practical flight
envelope.
(b) The SAS must be designed so that it cannot create a
hazardous deviation in flight path or produce hazardous loads on
the helicopter during normal operation or in the event of
malfunction or failure, assuming corrective action begins within an
appropriate period of time. Where multiple systems are installed,
subsequent malfunction conditions must be considered in sequence
unless their occurrence is shown to be improbable.
VIII. Equipment, systems, and installation. The basic
equipment and installation must comply with §§ 29.1303, 29.1431,
and 29.1433 through Amendment 29-14, with the following exceptions
and additions:
(a) Flight and Navigation Instruments. (1) A magnetic
gyro-stablized direction indicator instead of a gyroscopic
direction indicator required by § 29.1303(h); and
(2) A standby attitude indicator which meets the requirements of
§§ 29.1303(g)(1) through (7) instead of a rate-of-turn indicator
required by § 29.1303(g). For two-pilot configurations, one pilot's
primary indicator may be designated for this purpose. If standby
batteries are provided, they may be charged from the aircraft
electrical system if adequate isolation is incorporated.
(b) Miscellaneous requirements. (1) Instrument systems
and other systems essential for IFR flight that could be adversely
affected by icing must be adequately protected when exposed to the
continuous and intermittent maximum icing conditions defined in
appendix C of Part 29 of this chapter, whether or not the
rotorcraft is certificated for operation in icing conditions.
(2) There must be means in the generating system to
automatically de-energize and disconnect from the main bus any
power source developing hazardous overvoltage.
(3) Each required flight instrument using a power supply
(electric, vacuum, etc.) must have a visual means integral with the
instrument to indicate the adequacy of the power being
supplied.
(4) When multiple systems performing like functions are
required, each system must be grouped, routed, and spaced so that
physical separation between systems is provided to ensure that a
single malfunction will not adversely affect more than one
system.
(5) For systems that operate the required flight instruments at
each pilot's station -
(i) Only the required flight instruments for the first pilot may
be connected to that operating system;
(ii) Additional instruments, systems, or equipment may not be
connected to an operating system for a second pilot unless
provisions are made to ensure the continued normal functioning of
the required instruments in the event of any malfunction of the
additional instruments, systems, or equipment which is not shown to
be extremely improbable;
(iii) The equipment, systems, and installations must be designed
so that one display of the information essential to the safety of
flight which is provided by the instruments will remain available
to a pilot, without additional crewmember action, after any single
failure or combination of failures that is not shown to be
extremely improbable; and
(iv) For single-pilot configurations, instruments which require
a static source must be provided with a means of selecting an
alternate source and that source must be calibrated.
IX. Rotorcraft Flight Manual. A Rotorcraft Flight Manual
or Rotorcraft Flight Manual IFR Supplement must be provided and
must contain -
(a) Limitations. The approved IFR flight envelope, the
IFR flightcrew composition, the revised kinds of operation, and the
steepest IFR precision approach gradient for which the helicopter
is approved;
(b) Procedures. Required information for proper operation
of IFR systems and the recommended procedures in the event of
stability augmentation or electrical system failures; and
(c) Performance. If VYI differs from VY, climb
performance at VYI and with maximum continuous power throughout the
ranges of weight, altitude, and temperature for which approval is
requested.
X. Electrical and electronic system lightning protection. For
regulations concerning lightning protection for electrical and
electronic systems, see § 27.1316.
[Amdt. 27-19, 48 FR 4389, Jan. 31, 1983, as amended by Amdt. 27-44,
73 FR 11000, Feb. 29, 2008; Amdt. 27-46, 76 FR 33135, June 8, 2011]