CS-25 I25 Automatic Takeoff Thrust Control System (ATTCS)

(ATTCS) I 25.1 General (a) This Appendix specifies additional requirements and limitations for aeroplanes equipped with an engine control system that automatically resets thrust or power on the operating engine(s) when any engine fails during take-off, and for which performance credit is limited to that of paragraph 25.3(b) of this Appendix. When performance credit is not so limited, Special Conditions will apply. (b) With the ATTCS system and associated systems functioning normally as designed, all applicable requirements of CS-25, except as provided in this Appendix, must be met without requiring any action by the crew to increase thrust or power. I 25.2 Definitions (a) AutomaticTakeoff Thrust Control System (ATTCS). An ATTCS system is defined as a system which automatically resets thrust or power on the operating engine(s) when any engine fails during take-off. For the purpose of the requirements in this Appendix, the ATTCS system comprises all elements of equipment necessary for the control and performance of each intended function, including all devices both mechanical and electrical that sense engine failure, transmit signals and actuate fuel controls or power levers of the operating engine(s) to achieve scheduled thrust or power increases, the engine control system and devices which furnish cockpit information on system operation. (b) Critical Time Interval. When conducting an ATTCS take-off, the critical time interval is between one second before reaching V1, and the point on the gross take-off flight path with all engines operating where, assuming a simultaneous engine and ATTCS system failure, the resulting flight path thereafter intersects the gross flight path, determined in accordance with CS 25.115, at not less than 122 m (400 feet) above the take-off surface. This definition is shown in the following figure: I 25.3 Performance requirements All applicable performance requirements of CS-25 must be met with the ATTCS system functioning normally as designed, except that the propulsive thrust obtained from each operating engine after failure of the critical engine during take-off, and the thrust at which compliance with the one-engine-inoperative climb requirements in CS 25.121(a) and (b) is shown, must be assumed to be not greater than the lesser of – (a) The actual propulsive thrust resulting from the initial setting of power or thrust controls with the ATTCS system functioning normally as designed, without requiring any action by the crew to increase thrust or power until the aeroplane has achieved a height of 122 m (400 feet) above the take-off surface; or (b) 111 percent of the propulsive thrust which would have been available at the initial setting of power or thrust controls in the event of failure of the ATTCS system to reset thrust or power, without any action by the crew to increase thrust or power until the aeroplane has achieved a height of 122 m (400 feet) above the take-off surface. Note 1. The limitation of performance credit for ATTCS system operation to 111 percent of the thrust provided at the initial setting is intended to: (i) Assure an adequate level of climb performance with all engines operating at the initial setting of power or thrust controls, and (ii) Limit the degradation of performance in the event of a critical engine failure combined with failure of the ATTCS system to operate as designed. Note 2. For propeller-driven aeroplanes, propulsive thrust means the total effective propulsive force obtained from an operating engine and its propeller. I 25.4 Reliability requirements (See CS 25.1309 and AMC 25.1309) (a) The occurrence of an ATTCS system failure or a combination of failures in the ATTCS system during the critical time interval which – (1) Prevents the insertion of the required thrust or power, must be shown to be Improbable; (2) Results in a significant loss or reduction in thrust or power, must be shown to be Extremely Improbable. (b) The concurrent existence of an ATTCS system failure and an engine failure during the critical time interval must be shown to be Extremely Improbable. (c) The inadvertent operation of the ATTCS system must be shown either to be Remote or to have no more than a minor effect. I 25.5 Thrust or power setting The initial setting of thrust or power controls on each engine at the beginning of the take-off roll may not be less than the lesser of – (a) That required to permit normal operation of all safety-related systems and equipment dependent upon engine thrust or power lever position; or (b) That shown to be free of hazardous engine response characteristics when thrust or power is increased from the initial take-off thrust or power level to the maximum approved take-off thrust or power. I 25.6 Powerplant controls (a) General (1) In addition to the requirements of CS 25.1141, no single failure or malfunction, or probable combination thereof, of the ATTCS system, including associated systems, may cause the failure of any powerplant function necessary for safety. (2) The ATTCS system must be designed to perform accurately its intended function without exceeding engine operating limits under all reasonably expected conditions. (b) Thrust or Power Lever Control. The ATTCS system must be designed to permit manual decrease or increase in thrust or power up to the maximum thrust or power approved for use following engine failure during take-off through the use of the normal thrust or power controls, except that, for aeroplanes equipped with limiters that automatically prevent engine operating limits from being exceeded, other means may be used to increase thrust or power provided that the means is located in an accessible position on or close to the thrust or power levers, is easily identified, and operated under all operating conditions by a single action of either pilot with the hand that is normally used to actuate the thrust or power levers. (c) System Control and Monitoring. The ATTCS system must be designed to provide – (1) A means for checking prior to takeoff that the system is in an operable condition; and (2) A means for the flight crew to deactivate the automatic function. This means must be designed to prevent inadvertent deactivation. I 25.7 Powerplant instruments (a) System Control and Monitoring. A means must be provided to indicate when the ATTCS system is in the armed or ready condition. (b) Engine Failure Warning. If the inherent flight characteristics of the aeroplane do not provide adequate warning that an engine has failed, a warning system which is independent of the ATTCS system must be provided to give the pilot a clear warning of engine failure during take-off.