I. General. A transport 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 paragraphs IV (b) through (f) of this appendix.
The stick force must vary with speed so that any substantial speed change
results in a stick force clearly perceptible to the pilot. 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 paragraphs IV (b)
through (f) of this appendix.
(b) Climb. Stability must be shown in climb thoughout the speed
range 20 knots either side of trim with --
(1) The helicopter trimmed at VYI;
(2) Landing gear retracted (if retractable); and
(3) Power required for limit climb rate (at least 1,000 fpm) at VYI
or maximum continuous power, whichever is less.
(c) 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 --
(1) The helicopter trimmed and power adjusted for level flight at 0.9 VH
or 0.9 VNEI, whichever is lower; and
(2) Landing gear retracted (if retractable).
(d) 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 --
(1) The helicopter trimmed and power adjusted for level flight at 1.1 VMINI;
and
(2) Landing gear retracted (if retractable).
(e) Descent. Stability must be shown throughout the speed range
20 knots either side of trim with --
(1) The helicopter trimmed at 0.8 VH or 0.8 VNEI
(or 0.8 VLE for the landing gear extended case), whichever is
lower;
(2) Power required for 1,000 fpm descent at trim speed; and
(3) Landing gear extended and retracted, if applicable.
(f) 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 --
(1) The helicopter trimmed at the recommended approach speed or speeds;
(2) Landing gear extended and retracted, if applicable; and
(3) Power required to maintain a 3° glide path and power required to
maintain the steepest approach gradient for which approval is requested.
V. Static lateral-directional stability. (a) Static directional
stability must be positive throughout the approved ranges of airspeed,
power, and vertical speed. In straight, steady sideslips up to ±10° from
trim, directional control position must increase in approximately constant
proportion to angle of sideslip. At greater angles up to the maximum
sideslip angle appropriate to the type, increased directional control
position must produce increased angle of sideslip.
(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 cycle movement with sideslip must not be excessive.
VI. Dynamic stability. (a) Any oscillation having a period of
less than 5 seconds must damp to 1/2 amplitude in not more than one cycle.
(b) 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.
(c) Any oscillation having a period of 10 seconds or more but less than
20 seconds must be damped.
(d) Any oscillation having a period of 20 seconds or more may not
achieve double amplitude in less than 20 seconds.
(e) Any aperiodic response may not achieve double amplitude in less
than 9 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.
The occurrence of any failure condition which would prevent continued safe
flight and landing must be extremely improbable. For any failure condition
of the SAS which is not shown to be extremely improbable --
(1) The helicopter must be safely controllable and capable of prolonged
instrument flight without undue pilot effort. Additional unrelated
probable failures affecting the control system must be considered; and
(2) The flight characteristics requirements in Subpart B of Part 29
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 Subpart F of Part 29 through Amendment
29-14, with the following exceptions and additions:
(a) Flight and navigation instruments. (1) A magnetic
gyro-stabilized direction indicator instead of the 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). If standby batteries are provided, they may be charged
from the aircraft electrical system if adequate isolation is incorporated.
The system must be designed so that the standby batteries may not be used
for engine starting.
(b) Miscellaneous requirements. (1) Instrument systems and other
systems essential for IFR flight that could be adversely affected by icing
must be provided with adequate ice protection 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 crew-member 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.
(6) In determining compliance with the requirements of §29.1351(d)(2),
the supply of electrical power to all systems necessary for flight under
IFR must be included in the evaluation.
(c) Thunderstorm lights. In addition to the instrument lights
required by §29.1381(a), thunderstorm lights which provide high intensity
white flood lighting to the basic flight instruments must be provided. The
thunderstorm lights must be installed to meet the requirements of
§29.1381(b).
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.