АС 27-1A 7/30/97
(6) Self-Test Function. The CVR should be provided with a means in the cockpit which will allow a test to ensure the CVR is functioning properly. This may be accomplished by a manual playback feature.
(7) Bulk erasure. If this function is provided, the installation should be as follows:
Any probable malfunction will not cause erasure of the recording medium.
(iT) The crash impact forces will not cause activation of the bulk erasure function.
(iii) Inadvertent actuation of the bulk erasure function is minimized.
Usually, this is accomplished by requiring two separate actions to operate the bulk erasure.
707. § 27.1459 (Amendment 27-22) FLIGHT RECORDERS.
a. Explanation. The function of the flight recorder, sometimes referred to as a flight data recorder, is to provide a record of various aircraft and air data parameters during the operation of the rotorcraft. This data is utilized by accident investigators to 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, FADEC, 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, hydromechanical engine controls, 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.
938 Par 706
Airspeed. The installed flight recorder should record the airspeed with an accuracy of 3 percent or 5 knots (whichever is greater) from a speed of 20 knots to a speed of 80 percent more than Vy.
(ii) Flight Recorder. 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 should not exceed 150 feet.
(iii) Direction. The flight recorder should be capable of recording the magnetic heading of the rotorcraft within at least 10° for any heading. Larger deviations caused by the temporary operation of high current electrical devices such as heated windshields are acceptable.
(iv) Vertical Acceleration. The flight recorder should be capable of recording the normal acceleration of the center of gravity 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.
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 the 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.
(vi) Caveat. It should be noted that even though the requirements outlined above provide for compliance with the specific provisions of § 27.1459 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.i 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.
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(4) Electrical Power Supply. The rule requires that the flight recorder should be supplied with power from the most reliable source which does not jeopardize essential or emergency loads. 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:
(1) Any probable malfunction will not cause erasure of the recording medium.
(il) 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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708. § 27.1461 (Amendment 27-2) 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 § 27.1461 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 § 27.1461(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 rotorshaft. 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 § 27.1461(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 should not damage any components, systems, or surrounding structures that are essential for continued safe flight.
(3) If compliance with § 27.1461(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.
Par 708 941
709.-717. RESERVED.
Intentionally Left Blank Par 709 942 (thru 950)
SECTION 40. OPERATING LIMITATIONS
718. § 27.1501 (Amendment 27-14) GENERAL.
Explanation. 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 crew members as required in the various sections of this subpart.
719. § 27.1503 AIRSPEED LIMITATIONS: GENERAL.
a. Explanation. This section requires 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 limitations 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 720.
(ii) VNE (One-Engine-Inoperative (OEI)). See Paragraph 720.
(iii) VNE (Power-Off). See Paragraph 720.
(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.
(vi) Low Speed Flight Limitation. It is permissible for the applicant to establish minimum airspeed operating limitations as a function of weight, altitude, and temperature as long as there is still a practical flight envelope.
Par 718 951
(vii) MINI (Minimum FR Speed). The minimum speed for which compliance with the IF 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 for 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 following 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.
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 Augmentation Systems (SAS).
(B) Automatic Flight Control Systems (AFCS).
(C) Fly-by-Wire Elevator Systems (FBW).
(D) Air Data Computer Systems (ADC).
952 Par 719
(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 and maximum landing touchdown groundspeeds for utility type, float-gear-equipped rotorcraft. These wheel gear 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:
Maximum Groundspeed for Takeoff or Landing. The maximum acceptable groundspeed that can sately 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) Maximum Groundspeed for Brake Application. The maximum speed at which the wheel brakes may be applied without exceeding maximum brake energy capabilities should be determined for wheel 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.
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. Rather than limitations, operational information may be sufficient for skid type landing gear and for utility or float landing gear.
Par 719 953
720. § 27.1505 (Amendment 27-21) NEVER-EXCEED SPEED.
a. Explanation.
(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 Limit.
The all-engines-operating VNE is established by design and substantiated by flight tests. The VNE limits are the most conservative value that demonstrates compliance with the structural requirements (§ 27.309), the maneuverability and controllability requirements (§ 27.143), the stability requirements (§$ 27.173 and 27.175), or the vibration requirements (§ 27.251). 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 NE. The regulation restricts 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.
Rotorcraft that are equipped with airdata computers or other similar equipment are allowed to vary as many parameters as desired if the final result is 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 VNE that complies with the regulation in the event the airdata 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.
(u) To ensure compliance with the structural requirements (§ 27.309), vibration requirements (§ 27.251), and flutter requirements (§ 27.629), the all-engines-operating 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 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 with high advancing blade tip Mach number has shown that different types of rotor systems (articulated, semi-rigid, rigid, etc.) have various adverse characteristics. Therefore, it has been FAA/AUTHORITY policy to establish VNE 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, 954 Par 720
approved power-on rotor speed, and ambient temperature conditions. This policy was incorporated as a specific regulatory requirement with Amendment 27-21 to § 27.1505.
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.
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 NE 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.
(iv) A one-engine-inoperative (OEI) VNE is generally established through flight test and is usually near the Vu or VNE 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" VE and would be that speed at which the last remaining engine could be failed with satisfactory handling qualities. It is possible, although believed improbable, that a rotorcraft with more than two engines could have different VNES depending upon the number of engines still operating. It is recommended that the OEVNE not be significantly lower than the OEl best range airspeed. A multiengine rotorcraft may require an OEIVNE if the handling qualities following the last remaining engine failure are not satisfactory or if the rotor speed decays below the power-off transient limits at the all-engine-operating VNE-
(3) Power-off Limits. A power-off VNE may be established either by design or flight test and should be substantiated by flight tests. A power-off 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 NE 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 written, rotorcraft VNE speeds were significantly lower than those of Par 720 955
recently certificated rotorcraft. The high VNE speeds of current rotorcraft result in relatively high values for 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 VE is equal to or greater than the power-off speed for best range.
In any case, the power-off VE must be a high enough speed to be practical. A demonstration is required of the deceleration from the power-on VNE or OEIVNE to the power-off NE: The transition must be made in a controlled manner with normal pilot reaction and skill.
b. Procedures. The tests to substantiate the different VE 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 document. Static stability test techniques are covered in Paragraph 86 and the vibration test techniques in Paragraph 110.
721. § 27.1509 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 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-off 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 ensure 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.
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(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 § 27.33(a)(1) and (b)(1) for establishing the minimum power-on value. The reference to Paragraph (a)(1) is intended to ensure 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 (b)(1) establishes the requirement that the minimum power-on RPM can not be greater than the minimum RPM used to determine the appropriate setting of the main rotor high pitch stop.
Although the maximum power-on value is not specifically referred to in this section, it must be established as a limitation per § 27.309. In addition, for compliance with the requirements of § 27.141(b) regarding smooth transition from power-on to power-off flight, the power-on maximum limit should not be greater than the power-off maximum limit and the power-on minimum limit should not be less than the power-off minimum limit.
(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.
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 VNE (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 ensure 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 VNE (power-off) can either be decreased in accordance with § 27.1505(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 Par 721 957