aid in determination of the probable cause of an accident. The problems associated with acquisition of this data in aircraft not equipped with flight recorders has been complicated by the use of advanced instrument systems such as EFIS, EICAS, and IDS. The very nature of the operation of these systems precludes the deduction of post-accident data, as was possible with mechanical and electromechanical instruments, annunciators and switches. The National Transportation Safety Board (NTSB) therefore made a recommendation to the FAA that aircraft should be required to have flight recorders. Subsequently Congress mandated that flight recorders be required on many rotorcraft involved in passenger-carrying operations in accordance with FAR 91 and FAR 135.
b. Procedures. The following areas are of particular consideration in the approval of a flight data recorder installation.
(1) Equipment Qualification. The recommended procedure to obtain an approval for the flight recorder (and associated control panel, if appropriate) is to qualify the flight recorder to TSO C-124. The required underwater locating device should be qualified to the provisions of TSO C-121.
(2) Recorded Parameters and Accuracy.
(i) Airspeed. The installed flight recorder for a Category A rotorcraft should record the airspeed with an accuracy of 3 percent or 5 knots (whichever is greater) from a speed of 80 percent of VTOSS to VNE in level flight, and an accuracy of 10 knots from a speed 10 knots less than VTOSS to a speed of 10 knots more than VY in climb.
(ii) Pressure Altitude. The flight recorder should be capable of recording the pressure altitude of the rotorcraft with a range of -1,000 feet to the maximum certified altitude. The error of this recording at sea level, excluding instrument calibration error, should not exceed ±30 feet or a value of ±30 feet for each 100 knots of airspeed (whichever is greater).
(iii) Direction. The flight recorder should be capable of recording the magnetic heading of the rotorcraft within at least 10 degrees for any heading.
(iv) Vertical Acceleration. The flight recorder should be capable of recording the normal acceleration within the center of gravity range of the rotorcraft.
The recommended range of this recording is an envelope of -3 to +6 G with an accuracy of at least ±0.2 G.
(v) Time Correlation. The flight recorder should provide a time scaled correlation between the data recorded and the time at which this information was presented to the first pilot via his required flight instruments. This correlation should normally be established before flight, and should have an accuracy rate that does not diverge by more than 4 minutes and 4 seconds in 8 hours.
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(vi) Caveat. It should be noted that even though the requirements outlined above provide for compliance with the specific provisions of § 29.1459 regarding the acquired data and its accuracy, a flight recorder certified to these minimum standards will not meet the requirements of Appendix F of FAR 91 or Appendix C of FAR 135. If the flight recorder is to be used to comply with these operating rules, it is recommended that the appropriate appendix be consulted prior to requesting certification. The approved configuration may then be certified as meeting the requirements of the appropriate appendix.
(3) Flight Recorder Mechanical Installation. The non- ejectable flight recorder or the portion thereof which contains the recorded data should be physically located to enhance the probability of the recording surviving a crash. Normally, such a location would be in the lower portion of the rotorcraft as far aft as possible. However other locations in the rotorcraft may be suitable to meet the requirement to “minimize the probability of container rupture resulting from crash impact and subsequent damage to the record from fire.” The normal accelerometer should be located within the most restrictive center of gravity of the rotorcraft. The required underwater locator is usually mounted to the case of the flight recorder.
(4) Electrical Power Supply. The rule requires that the flight recorder should be supplied with power from a reliable source that does not jeopardize essential or emergency loads. For Category A rotorcraft, the flight recorder is not an essential load as specified in § 29.1309(e). However, since the functioning of the flight recorder is required by operating rules for some operations, it should be given priority over other nonessential loads.
(5) Self-Test Function. The flight recorder should be provided with a preflight test which will provide confirmation that the recorder and its recording medium are functioning properly.
(6) Data Erasure Feature. If this function is provided and the flight recorder is not powered solely by an engine or transmission driven generator, the installation should provide the following features:
(i) Any probable malfunction will not cause erasure of the recording medium.
(ii) The crash impact forces will not cause activation of the data erasure function.
(iii) Inadvertent actuation of the data erasure function is minimized.
Usually, this is accomplished by requiring two separate actions to operate the data erasure.
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AC 29.1461. § 29.1461 (Amendment 29-3) EQUIPMENT CONTAINING HIGH ENERGY ROTORS.
a. Explanation. This section contains requirements for the installation of equipment containing high energy rotors. A high energy rotor is any rotor which has sufficient kinetic energy to cause damage to surrounding structure, wiring, and equipment if a failure occurs. Turboshaft engine and APU rotors are not covered by this paragraph. One of the following requirements of § 29.1461 must be met.
(1) Paragraph (b) deals with damage tolerance, containment, and control devices.
(2) Paragraph (c) deals with containment and inoperative speed controls.
(3) Paragraph (d) deals primarily with equipment location.
b. Procedures.
(1) Compliance with § 29.1461(b) can be shown by a combination of analysis and test. A failure modes and effects and a stress analysis, together with a dynamic test, could be used to verify that the rotor would withstand the damage from environmental effects, and that the rotor case would contain any parts that may separate from the rotor shaft. The analysis and test should include a demonstration of the control device’s ability to prevent limitations from being exceeded.
(2) If compliance with the requirements of § 29.1461(c) is chosen, a test must be conducted which demonstrates that all parts from any type failure of a high energy rotor will be contained when that rotor is operating at the highest speed obtainable, with all speed control devices inoperative. This containment must not damage any components, systems, or surrounding structures that are essential for continued safe flight.
(3) If compliance with § 29.1461(d) is chosen, the location of the high energy rotor must be in an area where uncontained failed parts will not damage other components, systems, or surrounding structure which are essential for continued safe flight. It must also be shown that there is no possibility for failed, uncontained parts to enter the cabin area and endanger any occupant.
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CHAPTER 2. PART 29
AIRWORTHINESS STANDARDS
TRANSPORT CATEGORY ROTORCRAFT
SUBPART G - OPERATING LIMITATIONS AND INFORMATION AC 29.1501. § 29.1501 (Amendment 29-15) OPERATING LIMITATIONS - GENERAL.
This section simply requires specified operating limitations in addition to any other information necessary for the safe operation of the rotorcraft to be determined.
Secondly, it requires that this pertinent information be made readily available to the crewmembers as required in the various sections of this subpart.
OPERATING LIMITATIONS AC 29.1503. § 29.1503 AIRSPEED LIMITATIONS: GENERAL.
a. Explanation. This section requi res that a safe operating speed range be established for all rotorcraft. If the safe operating speed range varies with operating conditions (rotor speed, power, etc.), ambient conditions (altitude and/or temperature), rotorcraft configuration (gross weight, center of gravity, and/or external equipment), or type of operation (in ground effect (IGE), instrument flight rules (IFR), etc.), airspeed limitations that correspond with the most critical combinations of these factors must be established.
b. Procedures.
(1) Airspeed Limitations. The airspeed lim itations for each critical combination of factors are established by tests or analyses and verified by flight test. The following are airspeed limitations that are typically required depending on the particular rotorcraft design:
(i) VNE (Power On). See paragraph AC 29.1505.
(ii) VNE (One Engine Inoperative (OEI)). See paragraph AC 29.1505.
(iii) VNE (Power Off). See paragraph AC 29.1505.
(iv) VLO (Maximum Airspeed for Landing Gear Operation). Compliance with structural, handling qualities, and controllability requirements should be demonstrated at the airspeed limit.
(v) VLE (Maximum Airspeed Landing Gear Extended). If this airspeed limit differs from the maximum gear operation speed, compliance with the applicable structural, handling qualities, and controllability requirements should be demonstrated.
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(vi) Low Speed Flight Limitation. It is permissible for the applicant to establish a minimum airspeed operating limitation as a function of weight, altitude, and temperature as long as there is still a practical flight envelope.
(vii) VMINI (Minimum IFR Speed). The minimum speed for which compliance with the IFR handling qualities requirements has been demonstrated should be established as a limit for IFR operations.
(viii) Maximum Sideward and Rearward Flight Speed. The maximum demonstrated sideward flight or crosswind hover and rearward flight or tailwind hover airspeeds should be provided in the RFM. If these maximum speeds resulted from a control margin limitation, they should be included in the airspeed limitations section of the RFM. If adequate control margin remained fo r the critical combination of rotorcraft configuration and ambient conditions, the maximum demonstrated sideward or rearward flight airspeeds should be included in either the performance section or the limitations section of the RFM as the applicant desires.
(ix) Maximum Airspeeds for Special Configurations or Special Equipment.
Standard configuration airspeed limits frequently have to be reduced for specific changes or external modifications. The follo wing are examples of special equipment or configurations that have required additional airspeed limitations:
(A) Doors open or doors off.
(B) External hoist/cargo hook (stowed).
(C) Fixed or emergency flotation gear.
(D) External avionics equipment (large antennas, wires, etc.)
(E) External fuel tanks.
(F) Skid pad or ski equipment modifications to standard skid type landing gear.
(x) Maximum Airspeeds after Failure of Required Equipment. Rotorcraft that require auxiliary equipment such as stability augmentation systems to comply with FAR requirements throughout the approved operating envelope frequently require airspeed limitations following failure of part or all of this system in order to comply after the failure. The following are examples of auxiliary equipment that have required maximum airspeed limitations after failure of all or part of the system:
(A) Stability Augm entation Systems (SAS).
(B) Automatic Flight Control Systems (AFCS).
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(C) Fly-by-Wire Elevator Systems (FBW).
(D) Air Data Computer Systems (ADC).
(2) Groundspeed Limitations. Although not specifically required by this “airspeed limitations” regulation, it may be necessary to establish “groundspeed” limitations for wheel-gear-equipped rotorcraft. These limitations are required to show compliance with the ground-handling characteristic requirements, structural strength requirements, or the ground-loads requirements. However because of the operational similarity of groundspeed limits to airspeed limits, it is a common practice to include groundspeed limitations under the airspeed limitations heading in the flight manual. For this reason, groundspeed limitations are included in this paragraph of the AC.
Groundspeed limitations should be established with adequate safety margins to account for the possible inaccuracies associated with the necessity for the pilot to estimate groundspeed from indicated airspeed and available wind speed and direction information during actual operations. The following are examples of groundspeed limitations that have been required during past type certification programs:
(i) Maximum Groundspeed for Takeoff or Landing. The maximum acceptable groundspeed that can safely be used for wheel gear equipped rotorcraft takeoff and landing maneuvers should be determined based on landing gear limitations or ground controllability limitations. This speed should be fast enough to account for landing touchdown speeds at the maximum approved density altitude for normal takeoff and landing.
(ii) . The maximum speed at which the wheel b Maximum Groundspeed for Brake Application rakes may be applied without exceeding maximum brake energy capabilities should be determined for wheel gear equipped rotorcraft. This speed should be verified by test throughout the approved takeoff and landing envelope of the rotorcraft. The critical combination of gross weight and density altitude for brake energy considerations may be determined by analysis to minimize the required amount of testing. The maximum brake application groundspeed should be high enough to encompass brake application during landing at the maximum approved density altitude.
(iii) Other Groundspeed Limitations. For some rotorcraft designs with skid type landing gear, it may be necessary to establish a maximum landing touchdown speed for normal operations to comply with structural requirements. Optional equipment configurations such as float equipment, skis, etc., which are attached to conventional landing gear skids may require maximum landing groundspeed limits that are less than the limit for the basic rotorcraft.
AC 29.1505. § 29.1505 (Amendment 29-24) NEVER-EXCEED SPEED.
a. Explanation.
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AC 29-2C, Chg 1 2/12/03
(1) General. This rule requires the never -exceed speed (VNE) for both power-on and power-off flight to be established as operating limitations. The rule specifies how to establish and substantiate these limits.
(2) Power-on Limits.
(i) All Engines Operative (AEO).
(A) The all-engines-operating VNE is established by design and substantiated by flight tests. The V NE limits are the most conservative value that demonstrates compliance with the structural requirements (§ 29.309), the maneuverability and controllability requirements (§ 29.143), the stability requirements (§§ 29.173 and 29.175), or the vibration requirements (§ 29.251). The power -on VNE will normally decrease as density altitude or weight increases. A variation in rotor speed may also require a variation in the VNE. The regulation restricts to two the number of variables that are used to determine the VNE at any given time so that a single pilot can readily ascertain the correct VNE for his flight condition with a minimum of mental effort.
Helicopter manufacturers have typically presented never-exceed-speed limitation data as a function of pressure altitude and temperature. This information was placarded as well as contained in the flight manual. As the weight of some derivative models was increased, the FAA/AUTHORITY accepted altitude/temperature/VNE limitations that were categorized or contained within a weight range. Literal compliance with the regulation then required that the takeoff weight be calculated and then the indicated, appropriate airspeed limitation chart or placard be used for the entire flight. However, VNE charts or placards based on longitudinal center-of-gravity (c.g.) have been found to be unacceptable, since the same chart would potentially not be used throughout the flight and the pilot would thus be dealing with more than two variables to determine VNE.
Alternatively, rotorcraft that are equipped with air data computers or other similar equipment are allowed to vary as many parameters as desired, if the final results are no more than two parameters that define the VNE displayed to the pilot in an unambiguous manner. These rotorcraft must also have a method for determining V NE that complies with the regulation in the event the air data computer system fails. This method is usually more conservative than the automatic system because of the limitation in the number of parameters that can be varied.
(B) To ensure compliance with the structural requirements (§ 29.309), vibration requirements (§ 29.251), and flutter requirements (§ 29.629), the all-enginesoperating VNE should be restricted so that the maximum demonstrated main rotor tip mach number will not be exceeded at 1.11 VNE for any approved combination of altitude and ambient temperature. Previous rotorcraft cold weather tests have shown that the rotor system may exhibit several undesirable and possibly hazardous characteristics due to compressibility effects at high advancing blade tip mach numbers. As the center of pressure of the advancing rotor blade moves aft near the blade tip due to the formation of localized upper surface shock waves, rotor system loads may increase, the rotor system may exhibit an aerodynamic instability such as rotor weave, rotorcraft Page G - 4
vibration may increase substantially, and rotorcraft static or dynamic stability may be adversely affected. Which, if any, of these adverse characteristics are exhibited at high rotor tip mach numbers is dependent on the design of each particular rotor system.
FAA/AUTHORITY experience has shown some adverse characteristics exist for all the types of rotor systems (articulated, semirigid, rigid, etc.) and the various rotor blade designs evaluated at high advancing blade tip mach numbers during past certification programs. Therefore, it has been FAA/AUTHORITY policy to establish V NE so that it is not more than 0.9 times the maximum speed substantiated for advancing blade tip mach number effects for the critical combination of altitude, approved power-on rotor speed, and ambient temperature conditions. This policy was incorporated as a specific regulatory requirement with Amendment 29-24 to § 29.1505. High main rotor tip mach numbers obtained power off at higher than normal main rotor rotational speeds should not be used to establish the maximum power-on tip mach number VNE limit. In addition, since the onset of adverse conditions associated with high tip mach numbers can occur with little or no warning and amplify very rapidly, no extrapolation of the maximum demonstrated main rotor tip mach number VNE limitation should be allowed.
(C) A maximum speed for use of power in excess of maximum continuous power (MCP) should be established unless structural requirements have been substantiated for the use of takeoff power (TOP) at the maximum approved VNE airspeed. TOP is intended for use during takeoff and climb for not more than 5 minutes at relatively low airspeeds. However, FAA/AUTHORITY experience has shown that pilots will not hesitate to use TOP at much higher than best-rate-of-climb airspeeds unless a specific limitation against TOP use above a specified airspeed is included in the RFM. Structural and fatigue substantiations have not normally included loads associated with the use of TOP at VNE. Thus, a TOP airspeed limitation should be established from the structural substantiation data to preclude the accumulation of damaging rotor system and control mechanism loads through intentional use of the TOP rating at high airspeeds.
(ii) One Engine Inoperative (OEI). An OEI V NE is generally established through flight test and is usually near the OEI VH of the rotorcraft. It is the highest speed at which the failure of the remaining engine must be demonstrated. For rotorcraft with more than two engines, the appropriate designation would be “one-engine-operating” VNE and would be that speed at which the last remaining engine could be failed with satisfactory handling qualities. It is possible that a rotorcraft with more than two engines could have different VNE’s depending upon the number of engines still operating. It is recommended that the OEI V NE not be significantly lower than the OEI best range airspeed. For the last remaining engine failure case, a multiengine rotorcraft may require an OEI VNE if the handling qualities are not satisfactory, if the rotor speed decays below the power-off transient limits, or if any other unacceptable characteristic is found at speeds below the all-engine-operating VNE.
(3) Power-off Limits.
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(i) A power-off VNE may be established either by design or flight test and should be substantiated by flight tests. A power -off VNE that is less than the maximum power-on VNE is generally required if the handling qualities or stability characteristics at high speed in autorotation are not acceptable. A limitation of the power -off VNE may also be used if the rotorcraft has undesirable or objectionable flying qualities, such as large lateral-directional oscillations, at high autorotational airspeeds. The power -off VNE must meet the same criteria for control margins as the power-on VNE. The regulation requires that the power-off VNE be no less than the speed midway between the power-on VNE and the speed used to comply with the rate of climb requirements for the rotorcraft. When the regulation was w ritten, rotorcraft VNE speeds were significantly lower than those of recently certificated rotorcraft. The high V NE speeds of current rotorcraft result in relatively high values for the power-off VNE. Speeds lower than that specified in the regulation have been found acceptable through a finding of equivalent safety if the selected power-off VNE is equal to or greater than the power-off speed for best range. In any case, the power -off VNE must be a high enough speed to be practical. A demonstration is required of the deceleration from the power -on VNE for Category B rotorcraft, or OEI VNE for transport rotorcraft with Category A engine isolation, to the power-off VNE. The transition must be made in a controlled manner with normal pilot reaction and skill.
(ii) In addition to the minimum speed requirements for power-off VNE, the rule restricts the manner in which power-off VNE can be specified. Power -off VNE may be a constant airspeed which is less than power-on VNE for all approved ambient condition/gross weight combinations; a series of airspeeds varying with altitude, temperature or gross weight that is always a constant amount less than the power-on VNE for the same ambient condition/gross weight combination; or some combination of a constant airspeed for a portion of the approved altitude range and a constant amount less than power-on VNE for the remainder of the approved altitude range.
b. Procedures. The tests to substantiate the different V NE speeds are ordinarily conducted during the flight characteristics flight tests. The flight test procedures are discussed for the various limiting areas in earlier paragraphs of this AC. The controllability test techniques are covered in paragraph AC 29.143, static stability test techniques in paragraph AC 29.175, and the vibration test techniques in paragraph AC 29.251.
AC 29.1509. § 29.1509 ROTOR SPEED.
a. Explanation.
(1) General. This rule requires minimum and maximum power -off rotor speeds to be established as operating limitations. It also specifies the appropriate margins below and above these limits which must be substantiated structurally and by flight tests. In addition to addressing power -off limits, the rule requires that minimum Page G - 6
power-on RPM be established as an operating limit, and it specifies conditions, by reference, for establishing a minimum appropriate power-on speed.
(2) Power-o ff Limits. The power -off or autorotational RPM limits are established by design and substantiated by structural testing. Limits are confirmed during flight testing. Critical components must be designed for RPM values at least 5 percent above and below the maximum and minimum approved RPM values respectively. This 5 percent conservative speed requirement is in addition to the other structural safety factors built into the design requirements. A transient limit lower than the minimum in-flight RPM (power -off) will be defined to cover the final phase of a total power-off landing. Maximum weight is ordinarily critical for both tests. At low RPM, high coning angles can produce high stress levels in blade bending. Large flapping angles or controllability problems may also develop. At high RPM values, centrifugal forces on the blades are at their highest and stress levels on rotating components such as blade grips may be critical. If a particular model has a very large weight spread between minimum and maximum gross weights, the applicant may elect to specify two ranges of power-off RPM dependent upon weight. This may be needed to assure adequate power-off rotor RPM with collective full down without requiring the very low power-off rotor speeds at maximum weight, a condition which would be inappropriate for operation of the rotorcraft in service. Transient power -off RPM ranges may also be approved if needed for engine failure conditions; however, these transients must also be substantiated structurally and in flight.
(3) Power-on Limits. The minimum power -on rotor speed must be established so that it is no less than the minimum rotor speed which has been established structurally. The minimum power -on speed also cannot be less than those values achieved during any of the critical maneuvers during flight test substantiation of the rotorcraft. A 5 percent margin between the substantiated value and the limit value is not required as in the power-off case. This rule also makes reference to § 29.33(a)(1) and
(c)(1) for establishing the minimum power-on value. The reference to paragraph (a)(1) is intended to assure that the minimum power-on RPM value is low enough to accommodate the RPM values which will occur as a result of power changes and flight maneuvers expected in service. The reference to (c)(1) establishes the requirement that the minimum power-on RPM can be no lower than the minimum power-off RPM.
For single engine rotorcraft, this assures some transition capability to power-off flight conditions when an engine fails. For multiengine rotorcraft, it allows transition from power-on to power-off conditions as when transitioning from a cruise condition to a power-off descent. Although the maximum power -on value is not specifically referred to in this section, it must be established as a limitation per § 29.309. Since the considerations regarding smooth transition from power-on to power-off flight [reference § 29.141(b)] are similar to the minimum power-on condition described above, it may be inferred that maximum power-on RPM may not be greater than maximum power-off RPM.
(4) Transient Limits. Transient limits must be substantiated and approved in a similar manner. Transient limits may be outside of the steady state “red- line” limits.
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b. Procedures.
(1) Tests for substantiation of stress and vibration at the 5 percent underspeed and overspeed conditions in autorotation are ordinarily conducted as a part of the flight strain survey. For purposes of finding compliance with this rule, it is suggested that as a minimum, FAA/AUTHORITY certification personnel witness applicable portions of the test program and monitor telemetry or flight recorded data, as necessary, to verify compliance with this rule. Tests at maximum weight and at a relatively light weight condition are normally sufficient. Tests must be conducted at speeds up to V NE (power-off) at 105 percent of maximum RPM and 95 percent of minimum RPM. It is also appropriate to investigate speeds to 1.1 VNE (power-off) at maximum and minimum power-off RPM values. The normal low pitch stop may need to be downrigged in order to achieve the high RPM values at high speed. This feature should be coordinated with the manufacturer prior to the flight strain survey to assure necessary conditions are achieved. It may be difficult to obtain minimum power -off RPM prior to encountering retreating blade stall at combinations of high weight, high collective pitch, low rotor speed, and high forward speed. In this case V NE (power-off) can either be decreased in accordance with § 29.1505(c) or the low RPM range can be evaluated in a transient manner during engine failure testing at high speed. Any condition in which blade stall is suspected should, of course, be investigated with a great deal of caution and build-up testing is recommended. The transient low RPM limit for power -off landings may be tested only during actual power-off landings. In that case, the 5 percent margin is not required.
(2) Testing for suitable minimum and maximum power-on RPM values may be conducted during the designated FAA/AUTHORITY flight test program. The combined engine and governor response must allow accomplishment of all appropriate flight maneuvers without exceeding minimum or maximum power-on rotor limits. As in the power-off case, appropriate transient ranges and limits may be approved when properly substantiated. Transient ranges should be evaluated using similar methods and techniques to those described above. Power -on RPM determination must include not only rotor system considerations but engine and drive system characteristics as well. It is important to remember that all power-on ranges must be eligible under the Part 33 engine approval and that the power-off range must include adequate margins from potentially hazardous drive system phenomena, such as drive shaft whirl modes.
AC 29.1517. §29.1517 (Amendment 29-21) LIMITING HEIGHT-SPEED ENVELOPE.
a. Explanation.
(1) This section requires that the height-velocity (HV) envelope developed in compliance with § 29.79 of the performance requirements be established as an operating limitation for Category A rotorcraft.
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(2) For rotorcraft with FAR Part 29 and CAR Part 7 certification bases prior to Amendment 29-21, this section requires that the HV envelope be established as an operating limitation for Category B rotorcraft as well as Category A. The rule was revised by Amendment 29-21 to allow the HV envelope to be provided as performance information rather than as a limitation for rotorcraft meeting the revised § 29.1 Category B requirements. In addition, supplemental type certificates have been approved which allow Category B rotorcraft meeting the revised § 29.1(f) requirements to move the HV envelope from the limitations section to the performance section of the Rotorcraft Flight Manual (RFM). (See paragraph AC 29.1583.)
b. Procedures. T he limiting height-speed envelope developed in accordance with § 29.79 should be established as an operating limitation or as performance information to be included in the RFM in accordance with §§ 29.1583(f) and 29.1587(b)(6). (See paragraphs AC 29.79, AC 29.1583, and AC 29.1587 for additional information.)
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