CS 25.143 General

In showing compliance with the requirements of CS 25.143(a) and (b) account should be taken of aeroelastic effects and structural dynamics (including aeroplane response to rough runways and water waves) which may influence the aeroplane handling qualities in flight and on the surface. The oscillation characteristics of the flightdeck, in likely atmospheric conditions, should be such that there is no reduction in ability to control and manoeuvre the aeroplane safely.

1 An acceptable means of showing compliance with CS 25.143(b)(1) is to demonstrate that it is possible to regain full control of the aeroplane without attaining a dangerous flight condition in the event of a sudden and complete failure of the critical engine in the following conditions: a. At each take-off flap setting at the lowest speed recommended for initial steady climb with all engines operating after take-off, with – i. All engines, prior to the critical engine becoming inoperative, at maximum take-off power or thrust; ii. All propeller controls in the take-off position; iii. The landing gear retracted; iv. The aeroplane in trim in the prescribed initial conditions; and b. With wing-flaps retracted at a speed of 1.23 VSR1 with – i. All engines, prior to the critical engine becoming inoperative, at maximum continuous power or thrust; ii. All propeller controls in the en-route position; iii. The landing gear retracted; iv. The aeroplane in trim in the prescribed initial conditions. 2 The demonstrations should be made with simulated engine failure occurring during straight flight with wings level. In order to allow for likely delay in the initiation of recovery action, no action to recover the aeroplane should be taken for 2 seconds following engine failure. The recovery action should not necessitate movement of the engine, propeller or trimming controls, nor require excessive control forces. The aeroplane will be considered to have reached an unacceptable attitude if a bank angle of 45° is exceeded during recovery.

1.Background When full thrust or power is applied during a go-around, an excessive level of performance (rate of climb, accelerations) may be reached very quickly, and make it difficult for the flight crew to undertake all the actions required during a go-around, especially in an environment that is constrained (due to Air Traffic Control instructions, operational procedures, etc) and rapidly changing. This level of performance can also generate acceleration levels (in particular, forward linear accelerations) that could lead to spatial disorientation of the flight crew (e.g. a somatogravic illusion), in particular when combined with reduced visibility conditions and a lack of monitoring of primary flight parameters, such as pitch attitude. Accidents and incidents have occurred during or after go-arounds where somatogravic illusions have led flight crews to make inappropriate nose-down inputs, leading to an aircraft upset, a loss of control or a deviation from the normal go-around flight path, and in some cases, controlled flight into terrain with catastrophic consequences. Other accidents resulting in loss of control were due to excessive pitch attitudes combined with the flight crew’s inadequate awareness of the situation. The risk is higher on aeroplanes that have a large operational range of thrust to weight ratios, in particular for twin-engine aeroplanes and those with long-range capabilities.

2.Criteria for assessing the go-around manoeuvre risk with respect to somatogravic illusions and the flight crew workload

2.1 Somatogravic illusions It is considered that the risk of a somatogravic illusion is high when encountering high longitudinal acceleration or combined high values of pitch attitude (nose-up), pitch rate and longitudinal acceleration, associated with a loss of outside visual references.

2.2 Workload In order to provide sufficient time to the flight crew to manage its tasks, and therefore keep their workload at a reasonable level, longitudinal acceleration and vertical speed may need to be constrained. The assessment of the workload should be performed considering the basic workload functions described in Appendix D of CS-25.

2.3 Risk assessment and mitigation means There are no scientifically demonstrated aeroplane performance limits to ensure that the risks of somatogravic illusions and excessive workloads remain at acceptable levels. However, the following criteria should not be exceeded during a recommended go-around manoeuvre: a pitch rate value of 4 degrees per second, a pitch attitude of 20 degrees nose-up, an energy level corresponding to either: a vertical speed of 3 000 ft/min at constant calibrated airspeed, a climb gradient of 22 % at constant calibrated airspeed, or a level flight longitudinal acceleration capability of 7.8 km/h (4.2 kt) per second. Note 1: these boundaries should not affect operational performance, as they are considered to be beyond the operational needs for a go-around. Note 2: the numbers above should not be considered as hard limits, but as a reference only. Design mitigation means should be put in place in order to avoid exceeding these criteria and reduce the risk at an acceptable level. These means should: provide a robust method to reduce the risk identified, and be used during recommended go-around procedures. A reduced go-around (RGA) thrust or power function is considered to be an acceptable means of mitigation (refer to Chapter 4 below). Alternatively, exceeding any one of the above criteria should be duly justified by the applicant and accepted by EASA.

3.Go-around evaluation Go-around manoeuvres should be performed during flight testing in order to verify, in addition to the controllability and manoeuvrability aspects, that the flight crew workload and the risk of a somatogravic illusion are maintained at an acceptable level (for an acceptable level of risk of a somatogravic illusion, refer to Chapter 2.3 of this AMC). The go-around manoeuvres should be performed with all engines operating (AEO) and for each approved landing configuration as per the recommended AFM go-around procedure: with the most unfavourable, and practicable, combination of centre of gravity position and weight approved for landing, with any practicable combination of flight guidance/autothrust-throttle/autopilot to be approved, including manual, with a level-off altitude 1 000 ft above the go-around initiation altitude.

4.Implementation of a reduced go-around (RGA) thrust or power function The applicant may provide an RGA thrust or power function for use when the flight crew initiates a go-around. The function should operate with any practicable combination of the flight guidance/autothrust-throttle/autopilot modes to be approved for operation, including manual modes. This function should limit the engine thrust or power applied and maintain the performance of the aeroplane (in particular, its rate of climb) at a level that: is not less than the minimum required performance compatible with the operational needs and the flight crew workload during this phase; and reduces the flight crew’s risk of suffering a somatogravic illusion. This thrust or power reduction function may be available either through aircraft system automation or manually. In any case, acceptable procedure(s) should be available in the aeroplane flight manual (AFM), and the recommended go-around procedure should be based on the RGA thrust or power function. Note: When a reduced go-around thrust or power function is provided, the applicant should still use the most critical thrust or power within the range of available go-around thrust or power when showing compliance with the CS-25 specifications.

4.1 Design target RGA functions with a design target of a 2 000 ft/min rate of climb capability have been accepted by EASA.

4.2 Cockpit indications and information to the flight crew In automatic mode, information that thrust or power is reduced in the RGA mode should be indicated to the flight crew. In manual mode, the thrust level tables should be made available to the flight crew.

4.3 Evaluation An evaluation of the go-around manoeuvre with the RGA thrust or power function should be conducted following the recommendations of Chapter 3 above.

4.4 Thrust or power mode command It should be possible for the flight crew, at any time and without any delay, to select and apply the full go-around thrust or power. The applicant should provide specific procedures for which full thrust or power may be required, such as wind shear alert procedures, TCAS alert procedures, etc.

4.5 Engine failure during go-around with RGA thrust or power When an engine failure occurs during a go-around performed with active RGA thrust or power, if the required thrust or power from the remaining engine(s) to achieve an adequate performance level cannot be applied automatically, a warning alert to the flight crew is required to prompt them to take the necessary thrust or power recovery action. For non-moving autothrust-throttle lever designs or designs relying on manual thrust or power setting procedures, compelling flight deck alerts may be acceptable in lieu of automatic thrust or power recovery of the operating engine(s) to permit the use of maximum go-around thrust or power for compliance with CS 25.121 (d). The procedure for the recovery of the engine thrust or power setting must be demonstrated to be acceptable in terms of the detection of the situation by the pilot and the required actions in a high-workload environment. The following items should be evaluated: the timeliness of achieving the minimum required performance; flight crew awareness (indications, alerting…); flight crew actions (commands); the flight crew workload in general.

4.6 Performance published in the AFM for RGA thrust or power The climb performance required by CS 25.119 (in a landing climb, i.e. with all engines operating) should be based on the actual RGA thrust or power available (applied by following the recommended AFM procedure). The climb performance required by CS 25.121 (in an approach climb, i.e. with one engine inoperative) should be based on: either the RGA thrust or power available, if no thrust or power recovery is implemented, or the go-around thrust or power available after the application of the thrust or power recovery action (either automatically, or manually after an alert is triggered). For non-moving autothrust-throttle lever designs or manual thrust or power setting procedures, compelling flight deck alerts may be acceptable in lieu of automatic thrust or power recovery of the operating engine to permit the use of maximum go-around thrust or power for compliance with CS 25.121(d).

[Amdt 25/21]

[Amdt 25/26]

1 The maximum forces given in the table in CS 25.143(c) for pitch and roll control for short term application are applicable to manoeuvres in which the control force is only needed for a short period. Where the manoeuvre is such that the pilot will need to use one hand to operate other controls (such as the landing flare or go-around, or during changes of configuration or power resulting in a change of control force that must be trimmed out) the single-handed maximum control forces will be applicable. In other cases (such as take-off rotation, or manoeuvring during en-route flight) the two handed maximum forces will apply. 2 Short term and long term forces should be interpreted as follows:– Short term forces are the initial stabilised control forces that result from maintaining the intended flight path during configuration changes and normal transitions from one flight condition to another, or from regaining control following a failure. It is assumed that the pilot will take immediate action to reduce or eliminate such forces by re-trimming or changing configuration or flight conditions, and consequently short term forces are not considered to exist for any significant duration. They do not include transient force peaks that may occur during the configuration change, change of flight condition or recovery of control following a failure. Long term forces are those control forces that result from normal or failure conditions that cannot readily be trimmed out or eliminated.

[Amdt 25/3]

1 As an alternative to a detailed quantitative demonstration and analysis of coordinated turn capabilities, the levels of manoeuvrability free of stall warning required by CS 25.143(h) can normally be assumed where the scheduled operating speeds are not less than –

1.08 VSW for V2

1.16 VSW for V2 + xx, VFTO and VREF where VSW is the stall warning speed determined at idle power and at 1g in the same conditions of configuration, weight and centre of gravity, all expressed in CAS. Neverthless, a limited number of turning flight manoeuvres should be conducted to confirm qualitatively that the aeroplane does meet the manoeuvre bank angle objectives (e.g. for an aeroplane with a significant Mach effect on the CL/α relationship) and does not exhibit other characteristics which might interfere with normal manoeuvring. 2 The effect of thrust or power is normally a function of thrust to weight ratio alone and, therefore, it is acceptable for flight test purposes to use the thrust or power setting that is consistent with a WAT-limited climb gradient at the test conditions of weight, altitude and temperature. However, if the manoeuvre margin to stall warning (or other relevant characteristic that might interfere with normal manoeuvring) is reduced with increasing thrust or power, the critical conditions of both thrust or power and thrust-to-weight ratio must be taken into account when demonstrating the required manoeuvring capabilities.

[Amdt 25/3]