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CFR NPRM
 Federal Register Information
[Federal Register: December 18, 1980 (Volume 45, Number 245)]
[Page 83424]
 Header Information
Preamble Information
Regulatory Information
The Proposed Amendment
Accordingly, it is proposed to amend Part 27 and 29 of the Federal Aviation Regulations (14 CFR Parts 27 and 29) as follows:
Part 27 - Airworthiness Standards: Normal Category Rotorcraft
1. By revising Sec. 27.1(a) by deleting the period at the end of Sec. 27.1(a) and continuing that paragraph to read as follows:
Sec. 27.1 Applicability.
(a) * * * that have a passenger seating configuration, excluding pilot seats, of nine seats of less.
* * * * *
Explanation: This change is incorporated to retain consistency with proposed Sec. 29.1 See the explanation for proposed Sec. 29.1.
2. By deleting the word "and" at the end of Sec. 27.141(b)(1); by adding a new Sec. 27.141(b)(3); and by adding a sentence to the end of Sec. 27.141(c) to read as follows:
Sec. 27.141 General
* * * * *
(b) * * *
(3) Sudden, complete control system failures specified in Sec. 27.695 of this part; and
* * * * *
(c) * * * Requirements for helicopter instrument flight are contained in Appendix A of this part.
Explanation: The powered control system failure condition proposed in Sec. 27.141(b)(3) results from an HAA/AIA proposal which was added at the Rotorcraft Regulatory Review Conference in New Orleans. The HAA proposed consideration of single powered control system failures in the general flight characteristics requirements of Sec. 27.141(b). The FAA endorses this proposal and has referenced the single failure design requirements of Sec. 27.695 for consistency. Rotorcraft must be capable of continued safe flight in the event of any single failure of a powered control system. Adoption of this proposal would prevent loss of control and dangerous flight conditions in the event of any such failure and would ensure continued safe flight.
A sentence is added to Sec. 27.141(c) to provide a regulatory reference to the IFR criteria proposed for adoption in this notice. A substantively identical change is also proposed for Sec. 29.141.
Ref: Proposals 24, 26, 181, 182, 574, 575; Committee J.
Sec. 27.1419 [New]
3. By adding a new Sec. 27.1419 to read as follows:
(a) If certification with ice protection provisions is desired compliance with this section must be shown.
(b) The rotorcraft must demonstrate the capability to safely operate in the continuous maximum and intermittent maximum icing conditions determined under Appendix B of Part 29 of this chapter within the rotorcraft flight envelope. An analysis must be performed to establish, on the basis of the rotorcraft's operational needs, the adequacy of the ice protection system for the various components of the rotorcraft.
(c) In addition to the analysis and physical evaluation prescribed in paragraph (b) of this section, the effectiveness of the ice protection system and its components must be shown by flight tests of the rotorcraft or its components in measured atmospheric icing conditions and by one or more of the following tests as found necessary to determine the adequacy of the ice protection system:
(1) Laboratory dry air or simulated icing tests, or a combination of both, of the components or models of the components.
(2) Flight dry air tests of the ice protection system as a whole, or its individual components.
(3) Flight tests of the rotorcraft or its components in measured simulated icing conditions.
(d) The ice protection provisions of this section are considered to be applicable primarily to the airframe and rotor systems. For the powerplant installation, certain additional provisions of Subpart E of this part may be applicable.
(e) A means must be identified or provided for determining the formation of ice on critical parts of the rotorcraft. Unless otherwise restricted, the means must be available for nighttime as well as daytime operation. The rotorcraft flight manual must describe the means of determining ice formation and must contain information necessary for safe operation of the rotorcraft in icing conditions.
Explanation: Recent IFR certification and operation of normal category rotorcraft make icing certification a logical follow-on. Normal category rotorcraft must be able to operate safely in the natural icing environment if certification with ice protection provisions is desired. The icing environment in which normal and transport category rotorcraft must operate is the same. Appropriate icing criteria identical to that of proposed Sec. 29.1419 is therefore proposed for Part 27 rotorcraft. See the explanation for proposed Sec. 29.1419.
Ref: Proposals 92 and 275; Committee I.
4. By adding an Appendix A to Part 27 to read as follows:
Appendix A - 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 the helicopter meets the design and installation requirements contained in this appendix.
II. Definitions. (a) VYI means instrument climb speed, utilized in lieu of VY for compliance with the climb requirements for instrument flight.
(b) VNEI means instrument flight never exceed speed, utilized in lieu 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) 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. 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 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 20 knots either side of trim 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, steady sideslips, directional control position must increase proportionally with angle of sideslip, up to ±10° from trim. At greater angles of sideslip up to that at which full directional control is employed, or the maximum sideslip angle appropriate to the type is obtained, increased directional control position should produce increased angles 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 forces. 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 one-half 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 one-half 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 ore more or any aperiodic response may not achiever double amplitude in less than 20 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 one-half 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 or any aperiodic response may not achiever 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. The occurrence of any failure condition which would prevent continued safe flight and landing must be extremely improbable, or it must be shown that after any failure condition of the SAS that is not extremely improbable -
(1) The helicopter is safely controllable and is capable of prolonged instrument flight without undue pilot effort. Additional unrelated probable failures or combination of failures must be considered; and
(2) The flight characteristics requirements in Subpart B of Part 27 are met throughout a practical flight envelope.
(b) The SAS must be designed so that it cannot create 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. In addition to the basic equipment and installation requirements specified in Secs. 29.1303, 29.1309, and 29.1431 though Amendment 29-14, the following equipment must be installed:
(a) Instruments.
(1) In place of the requirement of Sec. 29.1303(h), a magnetic gyro stabilized direction indicator;
(2) In place of the requirement of Sec. 29.1303(i), an instantaneous vertical speed indicator (IVSI); and
(3) In place of the rate-of-turn indicator required by Sec. 29.1303(g), a standby attitude indicator which meets the requirements of Secs. 29.1303(g)(1) through (7). 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 deenergize and disconnect from the main bus any power source developing hazardous overvoltage.
(3) Each required flight instrument using a power supply must have a visual means integral with the instrument to indicate the adequacy of the power being supplied.
(4) When multiple systems 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 single pilot IFR -
(i) Only the required flight instruments for the pilot may be connected to the operating system provided for the pilot; and
(ii) Instruments which require a static source must be provided with a means of selecting an alternate source and that source must be calibrated.
(6) Dual pilot IFR. For systems that operate the required flight instruments which are located at each pilot's station -
(i) Means must be provided to connect the required instruments at the first pilot's station to operating systems which are independent of the operating systems at any other flight crew stations, or other equipment;
(ii) 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 the pilots, without additional crewmember action, after any single failure or combination of failures that is not shown to be extremely improbable; and
(iii) Additional instruments, systems, or equipment may not be connected to the operating systems for the required instruments, 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.
IX. Rotorcraft Flight Manual. A Rotorcraft Flight Manual or Rotorcraft Flight Manual IFR Supplement must be provided and it must contain the following:
(a) Limitations. The approved IFR flight envelope, the IFR flight crew 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.
(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.
Explanation: IFR certification standards for civil helicopters have been under development for many years. In 1952 a list of necessary IFR characteristics was set forth in paragraph 6.120-2(b) of a proposed CAM 6 supplement. In 1959, the list was updated, applied to the Cessna CH-1C (IFR), and found substantially sound for single pilot certification of that model in 1960. Since that time, the Civil IFR Standard has been updated periodically and applied during nearly 20 civil IFR helicopter type certification programs. This Appendix A proposal for helicopter instrument flight represents a consolidation of FAA, manufacturer, and user experience gathered since 1952 and refined in several versions of "The Interim Standard" for IFR certification of helicopters. Sources considered in drafting this proposal include the IFR military experience, military handling qualities specifications, including MIL-H-8501A, General Requirements for Helicopter Flying and Ground Handling Qualities, where applicable, experience of the research and development community, including simulation programs and variable stability helicopter studies, SFAR 29-2 operational experience, the type certification experience mentioned previously, the December 15, 1978, FAA Airworthiness Criteria for Helicopter Instrument Flight, and the HAA IFR proposal of December 4, 1979.
As discussed at the Rotorcraft Review Conference, the December 15, 1978, FAA Airworthiness Criteria for Helicopter Instrument Flight was substituted in its entirety for FAA proposals 151 and 413. The HAA counterproposal to the December 15 standard was compared and assessed in each of its requirements during drafting of this appendix. Portions of both the December 15 and HAA criteria are considered inappropriate for incorporation into a regulatory standard. Examples, techniques, and acceptable means of compliance are excluded in order that one acceptable means of compliance would not become the only acceptable means of compliance. Acceptable compliance procedures contained in the proposals, but not incorporated into the proposed appendix, will be included in a forthcoming revision to FAA Order 8110.32, Engineering Flight Test Guide for Transport Category Helicopters.
The proposed appendices for Parts 27 and 29 differ slightly. As is the case in the December 15, 1978, interim IFR standard, the handling qualities requirements for normal category two-pilot operation are relieving in two areas, static longitudinal stability and dynamic stability. The HAA proposed relief for two-pilot operation in both normal and transport categories. This would allow transport category two-pilot requirements which are less stringent than the single pilot requirements of normal category. It is inappropriate to permit less stringent handling qualities for transport category than for normal category, regardless of crew requirements. The concept of FAA's December 15, 1978, standard has been retained in this area and the appendices would provide lower requirements for the two-pilot condition in normal category only. Language in the normal category static stability requirement for two pilots is considered inappropriate for consideration in rule making. Phraseology such as "objectionable handling qualities" is overly subjective and is not enforceable as a minimum standard. In its place, positive static longitudinal stability is required for two pilots during cruise and approach conditions only. The proposed language retains the flexibility for the manufacturer to design around areas of instability for cruise through designation of VMINI and VNEI and through optimization of speed and gradient during approach. Areas of relaxed stability during climb, slow cruise, and descent could be found acceptable under the general flight characteristics requirements of Subpart B.
The climb condition is recognized as a critical demanding maneuver which typically represents a difficult design area for static longitudinal stability. If relief for the added two-pilot complement is to be meaningful, it must be addressed during climb. The FAA recognizes that during IFR climb pilots are highly attentive and the direction of motion of the vehicle is generally toward an open sector of airspace and away from contact with the surface. It is therefore considered appropriate to include relaxed two-pilot stability requirements for the climb condition.
Flight characteristics requirements should provide the capability to fly an equally accurate instrument approach regardless of whether the helicopter is certified for one or two pilots. The FAA considers static longitudinal stability an essential handling quality requirement during approach, and for this reason the single and two-pilot requirements during approach are identical. In addition, the static longitudinal stability paragraphs are reworded to provide a consistent format, and an airspeed reference is added to the descent requirement for the landing gear extended case in order that stability not be required beyond typical values for VLE. A 3° approach path is specified for compatibility with existing facilities and 3° remains the minimum requirement. Steeper approach angles were considered and are tied to demonstrations of static longitudinal stability in the proposal. The FAA does not intend to permit lower stability or a lower safety level for steep approach gradients. As such, steeper approach gradients are included under the approach stability stick force requirements of paragraph (IV)(b)(5).
The control system friction requirements contained in both FAA and HAA proposals are relaxed to allow greater return bands at high speed. The FAA considers the requirements to provide both positive slope and adequate margin at high speed an important but difficult design requirement which typically results in shallow cyclic position gradients. As such, the limit on cyclic friction band of ±10 knots is unnecessarily restrictive and this requirement would be expanded to ±10 percent of trim speed. This would result in no significant degradation in the level of safety for high cruise and descent conditions, but provides necessary relief for design.
The static lateral stability requirements are separated from directional stability in this proposal and are discussed as dihedral stability. Directional stability requirements would be incorporated without substantive change. The dihedral stability requirement of this proposal is intended as a compromise between the December 15 FAA proposal and the HAA counterproposal. Positive dihedral stability results in increasing right cyclic position and force when sideslipping with relative wind from the right. Stability definitions are not considered appropriate for the appendix and this feature is not included in the proposal. The FAA acknowledges that slightly relaxed dihedral stability is not necessarily detrimental to static and dynamic modes in rotorcraft, but the amount of relaxation must be constrained by control system sensitivity and by aircraft response characteristics, not by a fixed percent of cyclic travel. The intent of the proposal is to allow slightly negative dihedral stability that is within control system sensitivity, friction and component tolerances provided it is perceived as neutral up to ±10° of sideslip from trim. Fixed percentages of control system movement may or may not represent a significantly unstable gradient for any given helicopter. The FAA cannot permit a negative dihedral characteristic which results in reversed pilot force cues during sideslip condition. Such a characteristic results in a reversal in pilot perception and a source of considerable pilot confusion. Significant reversals in dihedral stability can also modify the lateral-directional dynamic characteristic to further introduce pilot confusion. The appendix as proposed would permit a very small amount of dihedral instability throughout the range of control system deadband, but would constrain it as a function of individual control system and rotorcraft design.
Dynamic stability requirements in the proposal are essentially identical to those from the December 15 standard for single pilot oscillatory conditions. The two-pilot oscillatory condition for periods exceeding 20 seconds is far more stringent than that for oscillations with a period between 10 and 20 seconds and provides no relaxation from the single pilot requirement. Minimum requirements for damping ratio should be inversely proportional to oscillatory frequency, and the two-pilot requirement for oscillations with a period greater than 20 seconds is not proposed. This feature is consistent with the HAA counterproposal.
Aperiodic response requirements are incorporated into the proposed amendment without the subjective references to pilot opinion utilized in previous proposals. Pilot perception of aperiodic responses is similar to that for oscillatory responses which exceed a 20-second period and typically result in gradual rates of divergence over the first few seconds of aircraft motion. Although lower in attitude rate and acceleration level than the oscillatory modes, aperiodic requirements have been held to the same level of divergence as oscillations with a 20-second period due to their more insidious nature. This concept provides safe and specific limits on aperiodic divergence. Greater rates of divergence are permitted for the normal category, two-pilot case.
Pilot delay times for stability system malfunction testing are excluded from this proposed amendment, as these criteria are more appropriately addressed in flight test guidance material. Representative time delays for typical designs will be included in a forthcoming revision to FAA Order 8110.32, Engineering Flight Test Guide for Transport Category Helicopters. Section VIII of this appendix is intended to establish criteria for equipment, systems, and their installations that are applicable to all rotorcraft, regardless of certification basis, when initially approved for IFR flight. The FAA has determined that Part 29, Subpart F through Amendment 29-14 and the additional criteria in section VIII of this appendix are adequate design criteria for IFR approved rotorcraft. The additional criteria in this appendix would require a gyro stabilized magnetic direction indicator in place of the gyro stabilized nonmagnetic direction indicator, an instantaneous vertical speed indicator in place of a standard vertical speed indicator, a standby attitude indicator with source of power independent of rotorcraft electrical system in place of rate-of-turn indicator, protection from icing effects for instruments affected by icing conditions, overvoltage protection for the electrical system, system separation for multiple systems to preclude a single fault causing loss of multiple systems, independence of the pilot's operating systems from other systems for single pilot approvals, an alternate static source for single pilot approvals, and instrument installation criteria for dual pilot approvals substantially identical to that required for transport airplanes.
Subpart F of Part 29 through Amendment 29-14 has been selected as the base on which IFR instrumentation criteria is built. Because navigation in instrument flight must be precise, the nonstabilized magnetic indicator, which is subject to many errors, is inadequate as the primary source of directional information, but it must remain as an emergency source. The standard directional gyro is also inadequate as the primary source of directional information because of drift and the requirement to set it by reference to some other precise reference. Therefore, a gyro stabilized magnetic direction indicator would be required.
The standard vertical speed indicator exhibits a significant delay in its indication. This delay is acceptable in rotorcraft VFR flight but unacceptable for IFR flight. More precise vertical speed information is needed to maintain flight path control in IFR conditions. Therefore, an instantaneous vertical speed indicator would be required. Section 29.1303(g) requires a rate-of-turn and slip-skid indicator, but allows in place of the rate-of-turn indicator a standby attitude indicator, provided it is independently powered from the rotorcraft's electrical system. Because total loss of the normal electrical system has proven to be probable, the FAA determined several years ago that transport aircraft in air carrier service must have an independently powered standby attitude indicator to assure continued safe flight in IFR conditions. A source of continued attitude reference is more important to rotorcraft IFR flight because of the natural instability of rotorcraft. Therefore, this appendix would require a standby attitude indicator.
Gross inaccuracies in altitude and airspeed indicators resulting from icing could be disastrous in IFR flight. Therefore, icing protection would be required by this appendix. Overvoltage of the electrical system could cause the failure of all electrically powered instruments and equipment. This could result in an extremely hazardous condition and this appendix requires overvoltage protection. Multiple systems are required because it is probable that at least one system would fail. Separation of such systems would preclude a single cable fault from causing a multiple system failure, and this appendix would so require. Independence of the pilot's operating systems from other systems to preclude such other system faults from possibly causing the loss of the pilot's system has been a requirement for IFR approved airplanes for many years, and this appendix would require it for single pilot IFR approval. Because loss of the pilot's static system could prove critical, an alternate calibrated source is considered essential for single pilot IFR approvals. This appendix requires an alternate source. As in various fixed wing applications, a protected, calibrated alternate static source could also be used to demonstrate compliance with the ice protection requirements of paragraph VIII(b)(1) of the appendix. The criteria for dual pilot IFR approval relative to instrument installations has been well established and proven in transport airplanes for many years. Proposal 376 of the rotorcraft regulatory review recommended that proven criteria be made a part of the rotorcraft transport rules and this proposal would utilize proven criteria for dual pilot IFR approval.
All flight manual requirements are consolidated from the FAA standard of December 15 into Section IX of the proposed amendment for clarity of presentation.
A requirement to incorporate cruise performance information into the IFR flight manual requirements was considered by FAA. Cruise performance information is not currently required by either fixed or rotary wing certificate standards. However, fixed wing manufacturers routinely provide this information to the pilot in a flight manual format. The FAA considers the availability of cruise performance information necessary for helicopter IFR flight and encourages and expects the manufacturers to provide this information.
Current Part 91 rules require the operating pilot to compute fuel requirements for IFR flights. Some helicopter manufacturers, however, have not provided the necessary information either in flight manuals or by other means. The result is that some operating pilots may have no method by which to compute fuel requirements for compliance with the operating rules. Flight manual cruise performance information for rotorcraft was addressed at the New Orleans conference during discussion of Proposals 146, 149, and 409 and was again discussed in the Rotorcraft Regulatory Review Meeting in Washington, D.C., on August 20, 1980. In those discussions, the HAA supported the concept of providing accurate cruise performance information for IFR flight and agreed to obtain from its manufacturers a commitment to provide this information, and to forward that commitment in writing to the FAA.
If cruise performance information is provided for helicopters in the manner discussed by the HAA, there will be no significant difference between helicopter cruise considerations and the current fixed wing condition. In order to retain consistency with the fixed wing standards, a requirement for cruise performance information is not included in this notice.
A similar requirement is also proposed for Appendix A to Part 29.
Ref. Proposals 151, 376, and 413; Committees I and II.
Part 29 - Airworthiness Standards: Transport Category Rotorcraft
5. By revising Secs. 29.1(a)(2) and 29.1(a)(3) to read as follows:
Sec. 29.1 Applicability.
(a) * * *
(2) Rotorcraft that meet the requirements for transport category B. Category B rotorcraft may not be certified with more than nine passenger seats. Category B rotorcraft with maximum gross weights greater than 20,000 pounds must be multiengine rotorcraft certified under the category A powerplant and system isolation requirements of Subpart D, E, and F of this part; or
(3) Multiengine rotorcraft that meet the requirements for transport category A and B.
* * * * *
Explanation
To summarize the present regulatory position and to expand on the background already presented, there are two rules (Parts 27 and 29) that regulate the certification of rotorcraft. Part 27 deals with rotorcraft that are under 6,000 pounds. Part 29, in effect, deals with rotorcraft that are over 6,000 pounds.
In Part 29, there are two categories of rotorcraft certification, category A and category B. Category A provides the most rigid rules, requiring independent engines, fuel systems and electrical systems. Category A requires that no single failure in these areas can cause simultaneous loss of more than one engine.
Category B of Part 29 deals with the certification of rotorcraft that are under 20,000 pounds. Currently these rotorcraft may be single or multiengine and may carry any number of passenger seats. Category B rotorcraft are not required to have the capability for continued flight in the event of an engine failure and must only demonstrate a safe landing to a defined surface after drift-down or autorotation.
The proposed changes to Parts 27 and 29 will provide a dividing line for rotorcraft based upon the number of passenger seats installed. A Part 27 rotorcraft must still be under 6,000 pounds. It is proposed, however, to add an additional limitation that the rotorcraft be equipped with nine or less passenger seats. Under the proposal, if the rotorcraft is equipped with more than nine passenger seats, it must be certificated under category A of Part 29.
The proposed rules will remove the restriction of 20,000 pounds on category B rotorcraft if certain design features are incorporated and will remove height-velocity as a category B limitation.
Under Part 29, a rotorcraft may be certificated under both categories A and B. At one gross weight, it may be certificated to carry more than nine passengers under category A provided it is able to continue flight in the event of an engine failure. It may also be certificated under category B to carry nine passengers or less with cargo, and take off at a higher gross weight that would not assure continued flight capability, but must demonstrate a safe landing to a defined surface in the event of an engine failure.
Statement of Proposal. Conference Proposals 5 through 8 and 152 through 155 contain suggested changes to the basic certification categories for rotorcraft. These proposals suggest that an overall deficiency exists in the current rules by addressing the need for a utility category for helicopters over 6,000 pounds and a need for consistency between fixed wing and rotary wing safety standards imposed when carrying passengers. These and other conference proposals generally support the concept and the content of the normal category certification standard contained in current Part 27 of this chapter. Two proponents suggest raising the 6,000-pound weight limit to 12,500 pounds and three proponents propose a maximum of nine passenger seats for normal category. Three proponents favor eliminating the 20,000-pound gross weight limit of category B. After considering each proposal and its applicable discussion, this consolidated proposal was drafted. This proposal in conjunction with other related proposals included in this notice would: (a) Remove the 20,000-pound weight limit of category B, but require multiengine category A design features for gross weights above 20,000 pounds; (b) remove height-velocity as a limitation for category B, but retain height-velocity capabilities as information to the pilot; and (c) limit Part 27 and transport category B certification to passenger seating configurations of nine seats or less, excluding pilot seats.
Current practice typically involves certification of multiengine transport category rotorcraft of less than 20,000 pounds to both category A and category B requirements. This proposal changes the word "or" in Sec. 29.1(a)(3) to "and" in order to clearly indicate the continued eligibility of a multiengine rotorcraft model for certification in both categories A and B under the proposed amendment. The words "and" at the end of current Sec. 29.1(a)(2) is changed to "or" in order to provide consistency with changed Sec. 29.1(a)(3).
Background Information
1. Definitions. "Category A" means multiengine rotorcraft incorporating engine isolation design features of Part 29 and utilizing scheduled takeoff and landing operations under a critical engine failure concept which assures adequate designated surface areas and adequate performance capabilities for continued safe flight in the event of engine failure.
"Category B" means single or multiengine rotorcraft for which landing is assumed in the event of an engine failure. Category B rotorcraft have no certified performance level or guaranteed stay-up-ability in the event of engine failure.
2. Discussion. Category A design requirements are contained primarily in the propulsion and systems sections of Part 29. They guarantee engine, fuel system, and electrical system independence so that no single failure in these areas can cause simultaneous loss of more than one engine. When category A design is shown, it allows consideration of only one engine failure at a time during critical conditions such as height-velocity, takeoff, and landing tests.
Category A flight operations include a critical engine failure concept or V1 concept similar to Part 25 or Appendix A to Part 135 of this chapter whereby runway lengths are scheduled so that, in the event an engine fails during takeoff at low speed, the rotorcraft is provided adequate surface conditions for landing. If the engine fails at some higher speed, the rotorcraft can continue the takeoff with guaranteed climb performance capabilities. Runway lengths for Category A landing operations are scheduled in a manner similar to that for takeoff. Unlike fixed wing aircraft, helicopters may require a significantly longer landing distance with an engine inoperative than with all engine inoperative than with all engines operating. Category A landing distances are schedules so that an engine can fail at any point and the rotorcraft can be satisfactorily landed at the destination facility. In Category A, occupants are assured of a safe flight capability with an engine failure at any point during flight.
Category B operations include no continued takeoff, continued flight, or destination landing capability in the event of engine failure. Operationally, if an engine fails in a category B rotorcraft; you do the best you can under the circumstances. Landing is assumed.
A direct parallel to category B may be drawn with single engine fixed wing aircraft or other fixed wing aircraft with nine passenger seats or less. When an engine fails, landing is assumed.
A parallel to category A may be drawn with fixed wing aircraft having 10 or more passenger seats. An engine failure can occur at any point after V1 and continued safe flight is assured.
Need for the Proposal. This proposal is a result of expanded helicopter capabilities and the general usage of helicopters in a manner different than that envisioned when the regulations differentiating between normal and transport category helicopters were formulated. Civil Air Regulations Draft Release No. 55-11, April 25, 1955, noted that the rotorcraft certification rule in effect at the time, Part 6 of the Civil Air Regulations, was based largely on experience with relatively small rotorcraft. No distinction was made between small and large rotorcraft or between rotorcraft intended for general and air carrier service. Part 6, therefore, was not suitable for the larger rotorcraft under development at that time. Consequently, Part 7 of the Civil Air Regulations was proposed to address rotorcraft which would be larger in size and intended for use in air carrier service. Three categories of rotorcraft were proposed in Draft Release No. 55-11, a "Normal Category" for relatively small rotorcraft and two transport categories, "A and B," applicable to large rotorcraft intended for air carrier service. Normal category rotorcraft were considered eligible for all VFR passenger and cargo operations for hire, except in certificated scheduled and irregular air carrier service. The size of normal category rotorcraft was limited by a 6,000-pound maximum weight. Transport category A rotorcraft were considered eligible for all types of operations including air carrier service under both VFR and IFR conditions. There was no limitation on maximum weight, but category A rotorcraft would be required to be multiengine and would be subject to appropriate performance operating limitations when used in air carrier service. Transport category B rotorcraft were considered eligible for air carrier and other operations only under VFR conditions. When used in air carrier service, transport category B rotorcraft would be subject to performance and route limitations. In addition, a 17,500-pound maximum weight limit (later revised to 20,000 pounds) was proposed for category B rotorcraft. It was proposed that category B rotorcraft be single or multiengined and it was intended that the provisions of category B be essentially similar to Part 6 already in effect at the time.
The concept of Transport Category Rotorcraft Airworthiness Regulations (with further subdivisions A and B) became affective with the adoption of Civil Air Regulations Part 7 on August 1, 1956. As previously noted, the originally proposed limit of 17,500 pounds for category B rotorcraft was changed to 20,000 pounds at that time, based on the expectations and advice of manufacturers. Both rotorcraft categories A and B were adopted into the rule with height-velocity as a limitation to assure a high level of safety for passenger carrying rules. The height-velocity envelope defines combinations of air speed and altitude at which safe landing is possible in the event of an engine failure. However, incorporation of height-velocity as a limit for category B later inhibited large helicopter usage in various utility applications. The regulations regarding applicability and category have remained basically unchanged with the recodification of Parts 6 and 7 to Federal Aviation Regulations 27 and 29, respectively.
The preamble to Part 7 recognizes the desirability of having significant operating experience with large rotorcraft prior to adopting specific airworthiness requirements. However, it further notes the benefit in terms of safety to be obtained by initial establishing "broad objective standards" and allowing wide discretion in approving unanticipated features. It was this basis on which the decision was made to adopt the proposed certification requirements by category of rotorcraft. In the intervening 25 years since the categorization of rotorcraft was formulated, considerable operating experience has been gained. During this period, significant improvements in rotorcraft capabilities have been made and the usage of rotorcraft has evolved somewhat differently than that originally envisioned. This proposal, accordingly, would update the certification rules to recognize those improvements, current uses, and future projections by recognizing the expanded uses and capabilities of transport category rotorcraft and recognizing a level of safety defined in terms of passenger capacity.
The proliferation of helicopter operations in a utility/cargo role, as distinguished from the basic task of transporting people between places, is well established. In addition, improvements in rotorcraft performance and efficiency have provided a capability for productive operations in category B at gross weights above 20,000 pounds. This capability, however, cannot be realized under the present rules which limit category B certification to helicopters of 20,000 pounds or less.
In the case of one large helicopter in excess of 20,000 pounds, certification to category A, per se, was inappropriate and it was necessary to apply category B type special conditions recognizing the rotorcraft's use solely in utility/cargo operations with no passenger carrying capability.
The need, therefore, clearly exists to utilize the increased capability of helicopters with appropriate design features for the utility role by permitting certification above 20,000 pounds in category B. In keeping with the concept of a category oriented primarily to utility/cargo helicopters, the productivity can be further enhanced by removing height-velocity requirements as an operating limitation for category B if appropriate restrictions are placed in the number of passengers carried. Related proposals are presented to accomplish this. These proposals would allow substantial growth in payload capacity consistent with industry projections for utility usage of helicopters.
As previously noted, the second major aspect of the applicability rules needing revision is that pertaining to passenger capacities. Contrary to earlier projections, the widespread transportation of fare-paying passengers in regularly scheduled helicopter air carrier service has not materialized. Operations under the category A performance concept are almost nonexistent. Most helicopter passenger-carrying operations are presently conducted under category B. Load-carrying capabilities of current transport category B helicopters permit carrying 10 or more passengers without the continued flight protection following engine failure provided by category A requirements. Carrying 10 or more passengers without this level of protection is inconsistent with the air carrier level of safety already in existence for fixed wing aircraft.
Under the original transport rotorcraft rule, FAA provided needed relief to helicopters by not requiring continued takeoff (category A) performance standards for all passenger carrying applications. Since that time, significant improvements have been made in the performance capability of helicopters and helicopter engines. The payload weight penalty for Category A operations as opposed to Category B has decreased as these improvements occurred. Therefore, helicopters can and should be operated at the same level of performance as their fixed wing counterparts. If passenger-carrying helicopters are to be accepted by the traveling public on an equal basis with fixed wing aircraft, they must provide passengers with a continued flight capability equivalent to that established for other aircraft. Accordingly, this proposal would eliminate the present disparity between helicopters and other aircraft carrying 10 or more passengers. This would be accomplished by limiting future certification of Part 29 category B, and Part 27 rotorcraft to nine passenger seats or less, thereby requiring rotorcraft with 10 or more passenger seats to be certified to Part 29 category A.
The total effect of these proposed changes would be to fill a need for an improved level of safety for rotorcraft passengers and to increase productivity of rotorcraft engaged in utility/cargo operations. This is consistent with the presidential and federal guidelines for formulating regulations and with FAA's dual responsibilities regarding aviation safety and the enhancement of air commerce.
Alternatives
1. Weight Limitations. The primary alternative considered at the Conference was to increase the Part 27 weight limit from 6,000 pounds to 12,500 pounds. While this would provide relief for aircraft between 6,000 and 12,500 pounds. Because of the evolution of rotorcraft technology and use, a certification rule is needed which will provide for utility rotorcraft over 12,500 pounds, it would not provide the needed relief for utility rotorcraft over 12,500 pounds. Because of the evolution of rotorcraft technology and use, a certification rule is needed which will provide for utility helicopters without regard to upper weight limits. The changes proposed in this notice would provide the needed relief throughout the weight range while continuing to assure the desired levels of safety for various types of operations.
2. Passenger Seating Limitations. At the Conference, the rotorcraft industry opposed using passenger seating capability to differentiate between categories. Industry representatives stated that the very same aircraft may have both 8 and 12 passenger seat configurations, and to invoke additional certification requirements only because of a few additional seats is not appropriate. The general philosophy behind this proposal on passenger seat limitations is that the higher the level of danger and the more people who fall within the endangered class the higher the level of safety should be. Because of the potentially hazardous conditions during failures as simple and as probable as the malfunctioning of a helicopter engine in flight and the large class of persons potentially affected, both size and number of passenger seats are considered relevant. The greater the number of passengers, the greater the potential loss of life in an accident. The greater the size and inertia of an aircraft, the greater the potential hazard to persons on the ground in the event of an accident.
A nine passenger line of demarcation has been determined for Parts 23 and 135 fixed wing aircraft, and has been justified under those amendments. The FAA has no evidence to indicate this number should not apply equally to rotorcraft.
Normal category rotorcraft carry relatively few passengers and constitute relatively little danger to persons on the surface in the event of an engine failure. Transport category rotorcraft have larger rotor systems with greater energy. They are, in general, less maneuverable, less capable of successfully autorotating to confined areas, and constitute a greater potential threat to persons on the surface in the event of an accident. For these reasons, the highest level of safety, transport category A, is proposed for rotorcraft carrying 10 or more passengers. A complementary requirement limiting passenger seats to nine or less is proposed for consistency in Part 27. Although helicopters presently certified in the normal category have passenger seating capacities of less than nine and the FAA is not aware of a forthcoming 10 passenger normal category helicopter in the 6,000-pound gross weight classification, the technology is available to produce such a helicopter. This proposal would establish Part 27 certification boundaries at 6,000 pounds gross weight and nine passenger seats.
The need for a rotorcraft utility category is well recognized. By limiting passenger capability of category B to nine or less, relaxed design standards may be reasonably justified. In this proposal, relief if provided to category B for both design and operational considerations below 20,000 pounds gross weight and for operational considerations above 20,000 pounds. Category B provisions allow carrying of some passengers for utility, work-related duties, or for other reasons without altering any category B flight requirements. Only large numbers of passengers, 10 or more, are prohibited. This restriction is necessary because height-velocity will no longer be a limitation for category B and a safe flight path following engine failure will no longer be assured for all flight conditions. Large numbers of passengers must be protected at all times against an accident resulting from engine failure. This philosophy is consistent with that contained in Parts 23 and 25 and Appendix A of Part 135; however, for rotorcraft, the utility category is restructured with no ties to pre-existing fixed wing concepts to allow realization of the unique operating capabilities of both large and small rotorcraft in utility roles.
Effect of Proposal. The effect of adopting this proposal would be to shift the safety emphasis toward large passenger carrying operations. Safety levels would be relaxed for the utility rotorcraft and increased for the 10 or more passenger rotorcraft. This action would provide certification standards for rotorcraft consistent with current operational needs and developmental projects. It would allow increased productivity for utility rotorcraft by deleting height-velocity as a limitation, thereby permitting many types of application which were previously prohibited.
Rotorcraft are projected to be carrying more and more passengers in business, commuter, and air carrier roles. This proposal would provide a clear and consistent 10 passenger division point for continued takeoff capability with engine failure for all fixed or rotary wing aircraft. The weight penalty to rotor craft for operation under the improved safety level of category A is parallel to that already experienced by fixed wing aircraft operating at the 10 passenger level and above. The tradeoffs between performance and weight are essentially the same in fixed and rotary wing aircraft. This proposal upgrades rotorcraft performance standards to those of their fixed wing counterparts. The economic and safety considerations of the continued takeoff philosophy for 10 or more passengers are discussed in considerable detail in NPRMS 67-11 (32 FR 5698; April 7, 1967) and 68-37 (34 FR 210; January 7, 1969) and in the preamble to Amendment 135-18 (35 FR 10098; June 19, 1970). Pertinent rulemaking philosophy and FAA's response to industry comments contained therein apply equally to this notice. In spite of dire predictions to the contrary, the current fixed wing air taxi industry is thriving under the 10 passenger requirement.
Enforcement. No unusual problems or penalties associated with enforcement of these proposed rule changes are anticipated.
Ref: Proposals 1, 5, 6, 7, 8, 152, 153, 154, and 155; Committees I and II.
6. By revising Sec. 29.79(a) to read as follows:
Sec. 29.79 Limiting height-speed envelope.
(a) If there is any combination of height and forward speed (including hover) under which a safe landing cannot be made under the applicable power failure condition in paragraph (b) of this section, a limiting height-speed envelope must be established for--
(1) Category A. Combinations of weight, pressure altitude, and ambient temperature for which takeoff and landing are approved; and
(2) Category B. (i) Altitude, from standard sea level conditions to the maximum altitude for which takeoff and landing are approved.
(ii) Weight, from the maximum weight (at sea level) to the highest weight approved for takeoff and landing at each altitude covered by paragraph (a)(2)(i) of this section. For helicopters, this weight need not exceed the highest weight allowing hovering out-of-ground-effect at each altitude.
* * * * *
Explanation: The proposed revision to the height-velocity (HV) requirement is necessitated by revisions to the applicability section of Part 29, removal of height velocity as a limitation for transport category B in proposed Sec. 29.1517 of this notice, and a corresponding proposal under consideration to specify HV weight requirements for normal category. Removal of HV as a limitation for transport category B effectively deletes the necessity to demonstrative HV capability to take off and landing WAT (Weight, Altitude, Temperature) limit conditions. This action, if adopted alone, would create an area subject to considerable interpretation in regard to aircraft weights selected by the applicant for demonstration of a HVC diagram. Even though HV is proposed as performance information and not as a limitation, specific weight requirements for demonstration of HV capability are needed to assure this information encompasses the gross weight capabilities of the helicopter and is therefore meaningful to the pilot throughout the conditions in which the pilot will operate. This proposal would place a lower limit on the weight selected for demonstration of HV capability and that weight would correspond to the takeoff and landing weight limit or the out-of-ground-effect hover capability of the helicopter, whichever is less. For additional background information regarding this proposal see the explanation under proposed Sec. 29.1 "Applicability."
Ref: Proposals 5 and 8, Committee I.
7. By deleting the word "and" at the end of Sec. 29.141(b)(1), adding a new Sec. 29.141(b)(3), and adding a sentence to the end of Sec. 29.141(c) to read as follows:
Sec. 29.141 General.
* * * * *
(b) * * *
(3) Sudden, complete control system failures specified in Sec. 29.695 of this part; and
(c) * * * Requirements for helicopter instrument flight are contained in Appendix A of this part.
Explanation: See the explanation for proposed Sec. 27.141.
8. By removing Sec. 29.877 and marking it "reserved".
Sec. 29.877 [Reserved]
Explanation: This proposal deletes Sec. 29.877 "Ice protection." A related proposal would establish the transport category rotorcraft icing requirements in a new Sec. 29.1419 "Ice protection," for consistency of section numbering with Parts 23 and 25 which contain icing certification requirements for fixed-wing aircraft in Secs. 23.1419 and 25.1419, respectively. The proposed Sec. 29.1419 contains updated and revised icing requirements compared to those in Sec. 29.877 as explained in that proposal. An additional related proposal would establish icing requirements for normal category rotorcraft in Sec. 27.1419
Ref: Proposals 92 and 275; Committee I.
9. By revising Sec. 29.1321(b) to read as follows:
Sec. 29.1321 Arrangement and visibility.
* * * * *
(b) Each instrument necessary for safe operation, including the airspeed indicator, gyroscopic direction indicator, gyroscopic bank and pitch indicator, slip-skid indicator, altimeter, rate-of-climb indicator, rotor tachometers, and the indicator most representative of engine power, must be grouped and centered as nearly as practicable about the vertical plane of the pilot's forward vision. In addition, for rotorcraft approved for IFR flight -
(1) The instrument that most effectively indicates attitude must be on the panel in the top center position;
(2) The instrument that most effectively indicates direction of flight must be adjacent to and directly below the attitude instrument;
(3) The instrument that most effectively indicates airspeed must be adjacent to and to the left of the attitude instrument; and
(4) The instrument that most effectively indicates altitude or is most frequently utilized in control of altitude must be adjacent to and to the right of the attitude instrument.
* * * * *
Explanation: Several conference proposals recommended making Sec. 29.1321(b) equivalent to Sec. 25.1321(b). One proposal recommend a 5 inch presentation be the minimum size for an attitude instrument, all instruments required by Sec. 29.1303 be included in Sec. 29.1321(b) grouping requirements, and the words "manifold pressure indicator" be changed to "power plant integrity indicator". Discussions at the conference acknowledged that the arrangement recommended by this proposal was generally used in existing rotorcraft, but several commenters expressed opposition to making it a requirement in transport category rotorcraft. There was much opposition to requiring a 5 inch attitude presentation. Although there was general agreement that the "manifold pressure indicator" should be changed to an indicator that was most representative of engine power, no agreement could be reached on what would constitute a power plant integrity indicator, and most participants indicated that they did not want it to be a specified instrument. The words "manifold pressure indication" are changed to "indicator most representative of engine power" in this proposal to make it equally applicable to turbine powered rotorcraft.
Instrument arrangement and visibility requirements for transport category airplanes are equally necessary for equal safety in transport category rotorcraft in IFR flight. The arrangement and visibility requirements (Basic "T" concept) of Part 25 of this chapter has been adopted in this proposal. Several IFR helicopter models have been FAA approved with the vertical velocity indicator in the upper right-hand portion of the display, a position normally reserved for the altimeter. This configuration was first approved on the IFR Gazelle in 1975 and has been carried forward to additional models since that time. For helicopters, this arrangement has been readily interpreted by pilots and has not resulted in cockpit confusion during IFR operations. This proposal includes the option to incorporate the instrument most frequently utilized for control of altitude in lieu of an altimeter in the basic instrument T. This flexibility is needed to permit the altimeter, vertical speed indicator, or possible future instrument designs to be incorporated into the basic IFR flight instrument display for helicopters. The instrumentation requirement is not needed for flight under visual flight rules; therefore, this proposed requirement in transport category rotorcraft is limited to rotorcraft approved for IFR flight.
The FAA agrees that attitude indicators must be effective in their presentation, but that size does not determine effectiveness, and therefore is dropping the proposed 5 inch attitude indicator requirement.
The standard gyroscopic turn-and-bank indicator is composed of two totally independent indicators, a rate-of-turn indicator and a "slip-skid indicator", frequently misidentified as a bank indicator. The rate-of-turn indicator has proven to be less effective in a rotorcraft than in a fixed wing aircraft while the slip-skid indicator has been found to be both necessary and effective in rotorcraft. Accordingly, the regulatory requirements for location of the turn and bank indicator relative to the vertical plane of the pilot's forward vision is amended to require only the "slip-skid indicator."
Ref: Proposals 369, 370, and 371; Committee II.
10. By adding a new Sec. 29.1419 to read as follows:
Sec. 29.1419 Ice protection
(a) If certification with ice protection provisions is desired, compliance with this section must be shown.
(b) The rotorcraft must demonstrate the capability to safely operate in the continuous maximum and intermittent maximum icing conditions determined under Appendix B of this part within the rotorcraft flight envelope. An analysis must be performed to establish, on the basis of the rotorcraft's operational needs, the adequacy of the ice protection system for the various components of the rotorcraft.
(c) In addition to the analysis and physical evaluation prescribed in paragraph (b) of this section, the effectiveness of the ice protection system and its components must be shown by flight tests of the rotorcraft or its components in measured natural atmospheric icing conditions and by one or more of the following tests as found necessary to determine the adequacy of the ice protection system.
(1) Laboratory dry air or simulated icing tests, or a combination of both, of the components or models of the components.
(2) Flight dry air tests of the ice protection system as a whole, or its individual components.
(3) Flight tests of the rotorcraft or its components in measured simulated icing conditions.
(d) The ice protection provisions of this section are considered to be applicable primarily to the airframe and rotor systems. For the powerplant installation, certain additional provisions of Subpart E of this part may be applicable.
(e) A means must be identified or provided for determining the formation of ice on critical parts of the rotorcraft. Unless otherwise restricted, the means must be available for nighttime as well as daytime operation. The rotorcraft flight manual must describe the means of determining ice formation and must contain information necessary for safe operation of the rotorcraft in icing conditions.
Explanation: This proposal would establish the transport category rotorcraft icing requirements in a new Sec. 29.1419 for consistency of section numbering with Parts 23 and 25. A related proposal would delete the existing Sec. 29.877 "Ice protection."
This proposal implements existing FAA policy. The current Sec. 29.877 implies that certification of helicopters with limited ice protection or in an icing environment somewhat less severe than the most severe defined natural conditions is feasible. Contrary to the intent of the recodification, which was essentially a format change, this implication was inadvertently included during the change from CAR 7 to Part 29. This implication is also contrary to current policy.
Considerable exchange has taken place through various mediums, including the regulatory review meetings in New Orleans and Washington, DC, relative to the possibility of limited icing certification or to some type of operational evaluation similar to that currently authorized by Special Federal Aviation Regulation (SFAR) 29-2 for helicopter IFR.
The possibility of limited icing certification has been carefully considered. The difficulty in forecasting the severity of icing conditions as well as the difficulty in relating the effects of reported icing conditions among different types of aircraft, and in particular between fixed and rotary wing aircraft, makes certification for limited icing conditions improbable at this time. Other concerns also militate against limited icing certification. Limited approvals have been made in other operating situations where the pilot has control of the limiting conditions. However, such is not the case with icing. Also, with limited ice protection or with a limited environmental approval, critical situations beyond the capability of the rotorcraft to operate safely may be readily encountered without viable escape alternatives.
The possibility of authorizing an operational icing evaluation similar to that permitted in SFAR 29-2 for IFR has been given serious and careful consideration. The situation in which SFAR 29-2 was approved is not comparable to the present situation regarding icing. There was considerable basis and experience with IFR certifications before SFAR 29-2 was approved; no helicopters have been certified in the U.S. for operation in icing. The limitations involved in an SFAR 29-2 operation are controllable by the pilot, the icing environment is not. The same concerns which apply to limited icing approvals are pertinent in this case. A limited icing operational approval by the United Kingdom Civil Aviation Authority has been suggested as a basis for rulemaking by the FAA. The United Kingdom approval is contingent on operation in a specific geographical area with unique environmental conditions which always provide an escape route in the event excessive icing conditions are encountered. Such a unique case would not be applicable to this proposal. The FAA must consider a much broader spectrum of conditions and applications for certification criteria. Therefore, limited icing approval is not included in this proposal.
On the other hand, the state-of-the-art in helicopter ice protection as displayed in military and foreign helicopter tests has shown that certification of helicopters in icing to the level of safety of fixed wing aircraft is feasible. It is therefore proposed to replace the existing Sec. 29.877 with essentially the same icing environment criteria that has been used for certification of fixed wing aircraft in Sec. 25.1419, with minor changes to adapt it to rotorcraft. The changes to convert Sec. 25.1419 to the proposed Sec. 29.1419 consist of -
(a) Substituting the word "rotorcraft" in place of "airplane" throughout the section;
(b) Changing reference to Appendix C of Part 25 in paragraph (b) to Appendix B of Part 29;
(c) Adding the words "within the rotorcraft flight envelope" in paragraph (b) in order to recognize the inherent altitude limitations of helicopters with regard to the altitude envelope of Appendix B;
(d) Deleting reference to turbine engines in paragraph (d), since Subpart E of this part addresses both reciprocating and turbine engines; and
(e) Adding a new paragraph (e) which contains a requirement for a means of indicating or of identifying the formation of ice on the critical parts of the rotorcraft. This is necessary as it would not be possible to visually ascertain the formation of ice on critical parts such as rotor blades or engine inlets in order to activate ice protection systems. Information for safe operation of the rotorcraft in icing conditions must also be included in the Rotorcraft Flight Manual.
(f) Adding Appendix B.
At the rotorcraft review conferences, the suggestion was made to defer rule making pending completion of ongoing icing research and development (R&D). Considerable R&D has been completed with FAA participation. This R&D has established the basic feasibility of operating helicopters with adequate ice protection systems in a natural icing environment. With this recognized, much of the R&D is now oriented toward refining techniques and reducing the time and cost associated with icing testing. The proposed rules simply define the icing environment, and the FAA sees no reason to defer rule making for icing certification in light of increased usage of helicopters in IFR and projected icing certification plans. A suggestion was also made at the rotorcraft review conference that the icing environment (Appendix C to Part 25 or Appendix B as proposed for this part) should be reassessed since it was defined by NACA 25 or 30 years ago.
Numerous icing certifications and years of operational experience with fixed wing aircraft have verified the soundness of the natural icing envelope, even though it was defined many years ago. This proposal recognizes that helicopters have a need to operate in the same basic environment as their fixed wing counterparts, except for high altitude portions of the envelope exclusive to the fixed wing aircraft.
A substantively identical change is also proposed for Sec. 27.1419.
Ref: Proposals 92 and 275; Committee I.
11. By revising the lead-in to Sec. 29.1517 to read as follows:
Sec. 29.1517 Limiting height-speed envelope.
For category A rotorcraft, if a range of heights exists at any speed.* * *
* * * * *
Explanation: See the explanation for proposed Sec. 29.1
12. By deleting the word "and" at the end of Sec. 29.1587(b)(5); by redesignating Sec. 29.1587(b)(6) as Sec. 29.1587(b)(7), and adding a new Sec. 29.1587(b)(6) to read as follows:
Sec. 29.1587 Performance Information.
* * * * *
(b) * * *
(6) The height-speed envelope; and
* * * * *
Explanation: See the explanation for proposed Sec. 29.1.
13. By adding an Appendix A to Part 29 to read as follows:
Appendix A - Airworthiness Criteria for Helicopter Instrument Flight
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 design and installation requirements contained in this appendix.
(a) VYI means instrument climb speed, utilized in lieu of VY for compliance with the climb requirements for instrument flight.
(b) VNEI means instrument flight never exceed speed, utilized in lieu of VNE for compliance with maximum limits speed requirements for instrument flight.
(c) VMINI means instrument flight minimum speed, utilized in complying with minimum limit speed requirements for instrument flight.
II. 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.
III. 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 throughout 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 20 knots either side of trim 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.
IV. 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, directional control position must increase proportionally with angle of sideslip up to ±10° from trim. At greater angles of sideslip up to that at which full directional control is employed, or the maximum sideslip angle appropriate to the type is obtained, increased directional control position should produce increased angles 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 forces. Longitudinal cycle movement with sideslip shall not be excessive.
V. Dynamic stability. (a) Any oscillation having a period of less than 5 seconds must damp to one-half 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 one-half 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 or any aperiodic response may not achieve double amplitude in less than 20 seconds.
VI. 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, or it must be shown that after any failure condition of the SAS that is not extremely improbable -
(1) The helicopter is safely controllable and is capable of prolonged instrument flight without undue pilot effort. Additional unrelated probable failures or combinations of failures must be considered; and
(2) The flight characteristics requirements in Subpart B of Part 29 are met throughout a practical flight envelope.
(b) The SAS must be designed so that it cannot create 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.
VII. Equipment, systems, and installation. In addition to the basic equipment and installation requirements specified in Subpart F of Part 29 through Amendment 29-14, the following equipment must be installed:
(a) Instruments. (1) In place of the requirement of Sec. 29.1303(h), a magnetic gyro stabilized direction indicator;
(2) In place of the requirement of Sec. 29.1303(i), and instantaneous vertical speed indicator (IVSI); and
(3) In place of the rate-of-turn indicator required by Sec. 29.1303(g), a standby attitude indicator which meets the requirements of Secs. 29.1303(g)(1) through (7). 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 deenergize and disconnect from the main bus any power source developing hazardous overvoltage.
(3) Each required flight instrument using a power supply must have a visual means integral with the instrument to indicate the adequacy of the power being supplied.
(4) When multiple systems are required, each system must be grouped, routed, and spaced so that physical separation between systems if provided to ensure that a single malfunction will not adversely affect more than one system.
(5) For single pilot IFR -
(i) Only the required flight instruments for the pilot may be connected to the operating system provided for the pilot; and
(ii) Instruments which require a static source must be provided with a means of selecting an alternate source and that source must be calibrated.
(6) Dual pilot IFR. For systems that operate the required flight instruments which are located at each pilot's station -
(i) Means must be provided to connect the required instruments at the first pilot's station to operating systems which are independent of the operating systems at any other flight crew stations, or other equipment;
(ii) 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 the pilots, without additional crewmember action, after any single failure or combination of failures that is not shown to be extremely improbable; and
(iii) Additional instruments , systems, or equipment may not be connected to the operating systems for the required instruments, 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 probable.
XIII. Rotorcraft Flight Manual. A Rotorcraft Flight Manual or Rotorcraft Flight Manual IFR Supplement must be provided and it must contain the following:
(a) Limitations. The approved IFR flight envelope, the IFR flight crew 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.
(c) Performance. If VYI differs from VY, climb performance at VYI and at maximum continuous power throughout the ranges of weight, altitude, and temperature for which approval is requested.
Explanation: See the explanation for proposed Appendix A of Part 27.
14. By adding an Appendix B to Part 29 to read as follows:
Appendix B
(a) Continuous maximum icing. The maximum continuous intensity of atmospheric icing conditions (continuous maximum icing) is defined by the variables of the cloud liquid water content, the mean effective diameter of the cloud droplets, the ambient air temperature, and the interrelationship of these three variables as shown in Figure 1 of this Appendix. The limiting icing envelope in terms of altitude and temperature is given in Figure 2 of this Appendix. The interrelationship of cloud liquid water content with drop diameter and altitude is determined from Figures 1 and 2. The cloud liquid water content for continuous maximum icing conditions of a horizontal extent, other than 17.4 nautical miles, is determined by the value of liquid water content of Figure 1, multiplied by the appropriate factor from Figure 3 of this Appendix.
(b) Intermittent maximum icing. The intermittent maximum intensity of atmospheric icing conditions (intermittent maximum icing) is defined by the variables of the cloud liquid water content, the mean effective diameter of the cloud droplets, the ambient air temperature, and the interrelationship of these three variables as shown in Figure 4 of this Appendix. The limiting icing envelope in terms of altitude and temperatures is given in Figure 5 of this Appendix. The interrelationship of cloud liquid water content with drop diameter and altitude is determined from Figures 4 and 5. The cloud liquid water content for intermittent maximum icing conditions of a horizontal extent, other than 2.6 nautical miles, is determined by the value of cloud liquid water content of Figure 4 multiplied by the appropriate factor in Figure 6 of this Appendix.
(Secs. 313(a), 601, 603, 604, Federal Aviation Act of 1958 (49 U.S.C. 1354(a), 1421, 1423, 1424); sec. 6(c) Department of Transportation Act (49 U.S.C. 1655(c)); and 14 CFR 11.45)
Note. - The FAA has determined that this document involves proposed regulations which are not considered to be significant under the procedures and criteria prescribed by Executive Order 12044 and as implemented by the Department of Transportation Regulatory Policies and Procedures (44 FR 11304; February 26, 1979). A copy of the draft evaluation prepared for this action is contained in the regulatory docket. A copy of it may be obtained from the person identified earlier in this document as contact for further information.
Footer Information
Issued in Washington, D.C., on December 15, 1980.
M. C. Beard,
Director of Airworthiness
[FR Doc. 80-39235 Filed 12-17-80; 8:45 am]
BILLING CODE 4010-13-M
Comments
Document History
Other Notice of Proposed Rulemaking Actions:
Not Applicable.
Final Rule Actions:
Final Rule. Docket No. 21180; Issued on 01/06/83.
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