AMC 25-13 Reduced and derated take-off thrust (power) procedures

• ED Decision 2021/015/R found in: CS-25 Amdt 27 - Large Aeroplanes (Jan 2023)

AMC 25-13 Reduced and derated take-off thrust (power) procedures ED Decision 2021/015/R 1 Purpose This acceptable means of compliance (AMC) provides guidance for the certification and use of reduced thrust (power) for take-off and derated take-off thrust (power) on turbine powered transport category aeroplanes. It consolidates CS guidance concerning this subject and serves as a ready reference for those involved with aeroplane certification and operation. These procedures should be considered during aeroplane type certification and supplemental type certification activities when less than engine rated take-off thrust (power) is used for take-off. 2 Related Certification Specifications (CS) The applicable regulations are [CS 25.101](#_DxCrossRefBm1709820709), [25.1521](#_DxCrossRefBm1709820849) and [25.1581](#_DxCrossRefBm1709820707). 3 Background Take-off operations conducted at thrust (power) settings less than the maximum take-off thrust (power) available may provide substantial benefits in terms of engine reliability, maintenance, and operating costs. These take-off operations generally fall into two categories; those with a specific derated thrust (power) level, and those using the reduced thrust (power) concept, which provides a lower thrust (power) level that may vary for different take-off operations. Both methods can be approved for use, provided certain limitations are observed. The subjects discussed herein do not pertain to in-flight thrust cutback procedures that may be employed for noise abatement purposes. 4 Definitions Customarily, the terms ‘thrust’ and ‘power’ are used, respectively, in reference to turbojet and turboprop installations. For simplicity, only the term ‘thrust’ is used throughout this AMC. For turboprop installations, the term ‘power’ should be substituted. For purposes of this AMC the following definitions apply: a. Take-off Thrust (1) Rated take-off thrust, for a turbojet engine, is the approved engine thrust, within the operating limits, including associated time limits, established by the engine type certificate for use during take-off operations. (2) Take-off thrust, for an aeroplane, is normally the engine rated take-off thrust, corrected for any installation losses and effects that is established for the aeroplane under CS-25. Some aeroplanes use a take-off thrust setting that is defined at a level that is less than that based on the engine rated take-off thrust. [CS 25.1521](#_DxCrossRefBm1709820849) requires that the take-off thrust rating established for the aeroplane must not exceed the take-off thrust rating limits established for the engine under the engine type certificate. The value of the take-off thrust setting parameter is presented in the Aeroplane Flight Manual (AFM) and is considered a normal take-off operating limit. b. Derated take-off thrust, for an aeroplane, is a take-off thrust less than the maximum take-off thrust, for which exists in the AFM a set of separate and independent, or clearly distinguishable, take-off limitations and performance data that complies with all the take-off requirements of CS-25. When operating with a derated take-off thrust, the value of the thrust setting parameter, which establishes thrust for take-off, is presented in the AFM and is considered a normal take-off operating limit. c. Reduced take-off thrust, for an aeroplane, is a take-off thrust less than the take-off (or derated take-off) thrust. The aeroplane take-off performance and thrust setting are established by approved simple methods, such as adjustments, or by corrections to the take-off or derated take-off thrust setting and performance. When operating with a reduced take-off thrust, the thrust setting parameter, which establishes thrust for take-off, is not considered a take-off operating limit. d. A ‘wet runway’ is one whose surface is covered by any visible dampness or water up to, and including, 3 mm deep within the intended area of use. e. A ‘contaminated runway’ is a runway where a significant portion of the runway surface area (whether in isolated areas or not) within the length and width being used is covered by one or more of the following substances: — compacted snow, — dry snow more than 3 mm deep, — heavy frost, — ice, — slush more than 3 mm deep, — standing water more than 3 mm deep, and — wet snow more than 3 mm deep. For the definitions of the contaminants, refer to Section 4 of [AMC 25.1591](#_DxCrossRefBm1709821830). f. A ‘slippery wet runway’ is a wet runway where the surface friction characteristics on a significant portion of the runway have been determined to be degraded. 5 Reduced Thrust: (Acceptable Means of Compliance) Under [CS 25.101(c)](#_DxCrossRefBm1709820709), [25.101(f)](#_DxCrossRefBm1709820709), and [25.101(h)](#_DxCrossRefBm1709820709), it is acceptable to establish and use a take-off thrust setting that is less than the take-off or derated take-off thrust if – a. The reduced take-off thrust setting – (1) Does not result in loss of systems or functions that are normally operative for take-off such as automatic spoilers, engine failure warning, configuration warning, systems dependent on engine bleed air, or any other required safety related system. (2) Is based on an approved take-off thrust rating or derating for which complete aeroplane performance data is provided. (3) Enables compliance with the applicable engine operating and aeroplane controllability requirements in the event that take-off thrust, or derated take-off thrust (if such is the performance basis), is applied at any point in the take-off path. (4) Is at least 60% of the maximum take-off thrust (no derate) for the existing ambient conditions, with no further reduction below 60% resulting from Automatic Take-off Thrust Control System (ATTCS) credit. Consequently the amount of reduced thrust permitted is reduced when combined with the use of derated thrust so that the overall thrust reduction remains at least 60 % of the maximum take-off thrust. For reduced thrust operations, compliance with the applicable performance and handling requirements should be demonstrated as thoroughly as for an approved take-off rating. (5) For turboprop installations, is predicated on an appropriate analysis of propeller efficiency variation at all applicable conditions and is limited to at least 75% take-off thrust. (6) Enables compliance with CS-25 Appendix I in the event of an engine failure during take-off, for aeroplanes equipped with an ATTCS. b. Relevant speeds (VEF, VMC, VR, and V2) used for reduced thrust take-offs are not less than those which will comply with the required airworthiness controllability criteria when using the take-off thrust (or derated take-off thrust, if such is the performance basis) for the ambient conditions, including the effects of an ATTCS. It should be noted, as stated in paragraph c. below, that in determining the take-off weight limits, credit can be given for an operable ATTCS. c. The aeroplane complies with all applicable performance requirements, including the criteria in paragraphs a. and b. above, within the range of approved take-off weights, with the operating engines at the thrust available for the reduced thrust setting selected for take-off. However, the thrust settings used to show compliance with the take-off flight path requirements of [CS 25.115](#_DxCrossRefBm1709820674) and the final take-off climb performance requirements of [CS 25.121(c)](#_DxCrossRefBm1709820672) should not be greater than that established by the initial thrust setting. In determining the take-off weight limits, credit can be given for an operable ATTCS. d. Appropriate limitations, procedures, and performance information are established and are included in the AFM. The reduced thrust procedures must ensure that there is no significant increase in cockpit workload, and no significant change to take-off procedures. e. A periodic take-off demonstration is conducted using the aeroplane’s take-off thrust setting without ATTCS, if fitted, and the event is logged in the aeroplane’s permanent records. An approved engine maintenance procedure or an approved engine condition-monitoring programme may be used to extend the time interval between take-off demonstrations. f. The AFM states, as a limitation, that take-offs utilising reduced take-off thrust settings: (1) Are not authorised on runways contaminated with standing water, snow, slush, or ice, and are not authorised on wet runways, including slippery wet runways, unless suitable performance accountability is made for the increased stopping distance on the wet surface. (2) Are not authorised where items affecting performance cause significant increase in crew workload. Examples of these are – Inoperative Equipment: Inoperative engine gauges, reversers, anti-skid systems or engine systems resulting in the need for additional performance corrections. Engine Intermix: Mixed engine configurations resulting in an increase in the normal number of power setting values. Non-standard operations: Any situation requiring a non-standard take-off technique. (3) Are not authorised unless the operator establishes a means to verify the availability of take-off or derated take-off thrust to ensure that engine deterioration does not exceed authorised limits. (4) Are authorised for aeroplanes equipped with an ATTCS, whether operating or not. g. The AFM states that – (1) Application of reduced take-off thrust in service is always at the discretion of the pilot. (2) When conducting a take-off using reduced take-off thrust, take-off thrust or derated take-off thrust if such is the performance basis may be selected at any time during the take-off operation. h. Procedures for reliably determining and applying the value of the reduced take-off thrust setting and determining the associated required aeroplane performance are simple (such as the assumed temperature method). Additionally, the pilot is provided with information to enable him to obtain both the reduced take-off thrust and take-off thrust, or derated take-off thrust if such is the performance basis, for each ambient condition. i. Training procedures are developed by the operator for the use of reduced take-off thrust. 6 Derated Thrust (Acceptable Means Of Compliance) For approval of derated take-off thrust provisions, the limitations, procedures, and other information prescribed by [CS 25.1581](#_DxCrossRefBm1709820707), as applicable for approval of a change in thrust, should be included as a separate Appendix in the AFM. The AFM limitations section should indicate that when operating with derated thrust, the thrust setting parameter should be considered a take-off operating limit. However, in-flight take-off thrust (based on the maximum take-off thrust specified in the basic AFM) may be used in showing compliance with the landing and approach climb requirements of [CS 25.119](#_DxCrossRefBm1709820701) and [25.121(d)](#_DxCrossRefBm1709820672), provided that the availability of take-off thrust upon demand is confirmed by using the thrust-verification checks specified in paragraph 5.e. above. [Amdt No: 25/2] [Amdt No: 25/13] [Amdt No: 25/27]