AMC1 29.1505 Never-exceed speed

• ED Decision 2023/001/R found in: CS-29 Amdt 11 - Large Rotercraft (Feb 2023)

AMC1 29.1505 Never-exceed speed ED Decision 2023/001/R This AMC replaces FAA AC 29-2C, § AC 29.1505 and should be used when showing compliance with [CS 29.1505](#_DxCrossRefBm1178331766). (a) Explanation (1) General [CS 29.1505](#_DxCrossRefBm1178331766) 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 VNE limits are the most conservative value that demonstrates compliance with the structural requirements ([CS 29.309](#_DxCrossRefBm1178331792)), the manoeuvrability and controllability requirements ([CS 29.143](#_DxCrossRefBm1178331719)), the stability requirements ([CS 29.173](#_DxCrossRefBm1178331770) and [CS 29.175](#_DxCrossRefBm1178331771)), or the vibration requirements ([CS 29.251](#_DxCrossRefBm1178331780)). 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 the 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, EASA and the FAA accepted altitude/temperature/ VNE limitations that were categorised or contained within a weight range. Literal compliance with the regulation then required that the take-off 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 centre of gravity 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 the VNE. Alternatively, rotorcraft that are equipped with modern avionics systems may be able to automatically calculate and display the VNE in an unambiguous manner as a function of the different parameters upon which it depends. For these designs, the applicant is expected to appropriately address the criticality associated with the loss and misleading presentation of the VNE when compliance of such systems with [CS 29.1309](#_DxCrossRefBm1178332097) is carried out. These rotorcraft should also have a method for determining the VNE that complies with the regulation for all failure conditions or combinations of failure conditions that are not extremely improbable. This method is usually more conservative than the automatic system because of the limitation in the number of parameters that can be varied. A placard may be used or appropriate RFM instructions. (B) To ensure compliance with the structural requirements ([CS 29.309](#_DxCrossRefBm1178331792)), vibration requirements ([CS 29.251](#_DxCrossRefBm1178331780)), and flutter requirements ([CS 29.629](#_DxCrossRefBm1178331873)), 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 centre of pressure of the advancing rotor blade moves aft near the blade tip due to the formation of localised 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. EASA and the FAA experience has shown that 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 programmes. Therefore, it has been EASA and the FAA 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, 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 take-off power (TOP) at the maximum approved VNE airspeed. TOP is intended for use during take-off and climb for not more than 5 minutes at relatively low airspeeds. However, EASA and the FAA 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 VNE 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 speeds depending upon the number of engines still operating. It is recommended that the OEI VNE 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 (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 written, rotorcraft VNE speeds were significantly lower than those of recently certificated rotorcraft. The high VNE speeds of current rotorcraft result in relatively high values for the Power-OFF VNE. Speeds lower than those 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 when it is not automatically calculated and displayed to the crew. To reduce the crew workload, in all the cases where the Power-OFF VNE is not automatically calculated, Power-OFF VNE may be a constant airspeed which is less than Power-ON VNE for all approved ambient conditions/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 VNE 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 AMC. The controllability test techniques are covered in § AC 29.143, static stability test techniques in § AC 29.175, and the vibration test techniques in § AC 29.251. [Amdt No: 29/11] ##### AMC1 29.1505 Never-exceed speed *ED Decision 2023/001/R* This AMC replaces FAA AC 29-2C, § AC 29.1505 and should be used when showing compliance with [CS 29.1505](#_DxCrossRefBm1685772231). (a) Explanation (1) General [CS 29.1505](#_DxCrossRefBm1685772231) 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 VNE limits are the most conservative value that demonstrates compliance with the structural requirements ([CS 29.309](#_DxCrossRefBm1685772257)), the manoeuvrability and controllability requirements ([CS 29.143](#_DxCrossRefBm1685772184)), the stability requirements ([CS 29.173](#_DxCrossRefBm1685772235) and [CS 29.175](#_DxCrossRefBm1685772236)), or the vibration requirements ([CS 29.251](#_DxCrossRefBm1685772245)). 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 the 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, EASA and the FAA accepted altitude/temperature/ VNE limitations that were categorised or contained within a weight range. Literal compliance with the regulation then required that the take-off 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 centre of gravity 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 the VNE. Alternatively, rotorcraft that are equipped with modern avionics systems may be able to automatically calculate and display the VNE in an unambiguous manner as a function of the different parameters upon which it depends. For these designs, the applicant is expected to appropriately address the criticality associated with the loss and misleading presentation of the VNE when compliance of such systems with [CS 29.1309](#_DxCrossRefBm1685772562) is carried out. These rotorcraft should also have a method for determining the VNE that complies with the regulation for all failure conditions or combinations of failure conditions that are not extremely improbable. This method is usually more conservative than the automatic system because of the limitation in the number of parameters that can be varied. A placard may be used or appropriate RFM instructions. (B) To ensure compliance with the structural requirements ([CS 29.309](#_DxCrossRefBm1685772257)), vibration requirements ([CS 29.251](#_DxCrossRefBm1685772245)), and flutter requirements ([CS 29.629](#_DxCrossRefBm1685772338)), 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 centre of pressure of the advancing rotor blade moves aft near the blade tip due to the formation of localised 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. EASA and the FAA experience has shown that 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 programmes. Therefore, it has been EASA and the FAA 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, 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 take-off power (TOP) at the maximum approved VNE airspeed. TOP is intended for use during take-off and climb for not more than 5 minutes at relatively low airspeeds. However, EASA and the FAA 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 VNE 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 VNEspeeds depending upon the number of engines still operating. It is recommended that the OEI VNE 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 (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 written, rotorcraft VNE speeds were significantly lower than those of recently certificated rotorcraft. The high VNE speeds of current rotorcraft result in relatively high values for the Power-OFF VNE. Speeds lower than those 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 when it is not automatically calculated and displayed to the crew. To reduce the crew workload, in all the cases where the Power-OFF VNE is not automatically calculated, Power-OFF VNE may be a constant airspeed which is less than Power-ON VNE for all approved ambient conditions/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 VNE 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 AMC. The controllability test techniques are covered in § AC 29.143, static stability test techniques in § AC 29.175, and the vibration test techniques in § AC 29.251. [Amdt No: 29/11]