CS 25.201 Stall demonstration

ED Decision 2016/010/R

(a) Stalls must be shown in straight flight and in 30° banked turns with –

(1)  Power off; and

(2) The power necessary to maintain level flight at 1·5 VSR1 (where VSR1 corresponds to the reference stall speed at maximum landing weight with flaps in the approach position and the landing gear retracted. (See AMC 25.201(a)(2).)

(b) In each condition required by sub-paragraph (a) of this paragraph, it must be possible to meet the applicable requirements of CS 25.203 with –

(1) Flaps, landing gear and deceleration devices in any likely combination of positions approved for operation; (See AMC 25.201(b)(1).)

(2) Representative weights within the range for which certification is requested;

(3) The most adverse centre of gravity for recovery; and

(4) The aeroplane trimmed for straight flight at the speed prescribed in CS 25.103(b)(6).

(c) The following procedures must be used to show compliance with CS 25.203:

(1) Starting at a speed sufficiently above the stalling speed to ensure that a steady rate of speed reduction can be established, apply the longitudinal control so that the speed reduction does not exceed 0.5 m/s2 (one knot per second) until the aeroplane is stalled. (See AMC 25.103(c).)

(2) In addition, for turning flight stalls, apply the longitudinal control to achieve airspeed deceleration rates up to 5,6 km/h (3 kt) per second. (See AMC 25.201(c)(2).)

(3) As soon as the aeroplane is stalled, recover by normal recovery techniques.

(d) The aeroplane is considered stalled when the behaviour of the aeroplane gives the pilot a clear and distinctive indication of an acceptable nature that the aeroplane is stalled. (See AMC 25.201(d).) Acceptable indications of a stall, occurring either individually or in combination, are –

(1) A nose-down pitch that cannot be readily arrested;

(2) Buffeting, of a magnitude and severity that is a strong and effective deterrent to further speed reduction; or

(3) The pitch control reaches the aft stop and no further increase in pitch attitude occurs when the control is held full aft for a short time before recovery is initiated. (See AMC 25.201(d)(3).)

[Amdt 25/18]

AMC 25.201(a)(2) Stall demonstration

ED Decision 2003/2/RM

The power for all power-on stall demonstrations is that power necessary to maintain level flight at a speed of 1·5 VSR1 at maximum landing weight, with flaps in the approach position and landing gear retracted, where VSR1 is the reference stall speed in the same conditions (except power). The flap position to be used to determine this power setting is that position in which the reference stall speed does not exceed 110% of the reference stall speed with the flaps in the most extended landing position.

AMC 25.201(b)(1) Stall demonstration

ED Decision 2003/2/RM

Stall demonstrations for compliance with CS 25.201 should include demonstrations with deceleration devices deployed for all flap positions unless limitations against use of the devices with particular flap positions are imposed. ‘Deceleration devices’ include spoilers when used as air brakes, and thrust reversers when use in flight is permitted. Stall demonstrations with deceleration devices deployed should normally be carried out with power off, except where deployment of the deceleration devices while power is applied is likely to occur in normal operations (e.g. use of extended air brakes during landing approach).

AMC 25.201(c)(2) Turning Flight Stalls At Higher Deceleration Rates

ED Decision 2003/2/RM

The intent of evaluating higher deceleration rates is to demonstrate safe characteristics at higher rates of increase of angle of attack than are obtained from the 0.5 m/s2 (1 knot per second) stalls. The specified airspeed deceleration rate, and associated angle of attack rate, should be maintained up to the point at which the aeroplane stalls.

AMC 25.201(d) Stall demonstration

ED Decision 2018/005/R

1 The behaviour of the aeroplane includes the behaviour as affected by the normal functioning of any systems with which the aeroplane is equipped, including devices intended to alter the stalling characteristics of the aeroplane.

2 Unless the design of the automatic flight control system of the aeroplane protects against such an event, the stalling characteristics and adequacy of stall warning, when the aeroplane is stalled under the control of the automatic flight control system, should be investigated. (See also CS 25.1329(h).)

[Amdt 25/19]

[Amdt 25/21]

AMC 25.201(d)(3) Stall demonstration

ED Decision 2003/2/RM

An acceptable interpretation of holding the pitch control on the aft stop for a short time is:

a. The pitch control reaches the aft stop and is held full aft for 2 seconds or until the pitch attitude stops increasing, whichever occurs later.

b. In the case of turning flight stalls, recovery may be initiated once the pitch control reaches the aft stop when accompanied by a rolling motion that is not immediately controllable (provided the rolling motion complies with CS 25.203(c)).

c. For those aeroplanes where stall is defined by full nose up longitudinal control for both forward and aft C.G., the time at full aft stick should be not less than was used for stall speed determination, except as permitted by paragraph (b) above.

CS 25.203 Stall characteristics

ED Decision 2003/2/RM

(See AMC 25.203.)

(a) It must be possible to produce and to correct roll and yaw by unreversed use of aileron and rudder controls, up to the time the aeroplane is stalled. No abnormal nose-up pitching may occur. The longitudinal control force must be positive up to and throughout the stall. In addition, it must be possible to promptly prevent stalling and to recover from a stall by normal use of the controls.

(b) For level wing stalls, the roll occurring between the stall and the completion of the recovery may not exceed approximately 20°.

(c) For turning flight stalls, the action of the aeroplane after the stall may not be so violent or extreme as to make it difficult, with normal piloting skill, to effect a prompt recovery and to regain control of the aeroplane. The maximum bank angle that occurs during the recovery may not exceed –

(1) Approximately 60° in the original direction of the turn, or 30°in the opposite direction, for deceleration rates up to 0.5 m/s2 (1 knot per second); and

(2) Approximately 90° in the original direction of the turn, or 60°in the opposite direction, for deceleration rates in excess of 0.5 m/s2 (1 knot per second).

AMC 25.203 Stall characteristics

ED Decision 2003/2/RM

1 Static Longitudinal Stability during the Approach to the Stall.  During the approach to the stall the longitudinal control pull force should increase continuously as speed is reduced from the trimmed speed to the onset of stall warning. At lower speeds some reduction in longitudinal control pull force will be acceptable provided that it is not sudden or excessive.

2 Rolling Motions at the Stall

2.1 Where the stall is indicated by a nose-down pitch, this may be accompanied by a rolling motion that is not immediately controllable, provided that the rolling motion complies with CS 25.203(b) or (c) as appropriate.

2.2 In level wing stalls the bank angle may exceed 20° occasionally, provided that lateral control is effective during recovery.

3 Deep Stall Penetration. Where the results of wind tunnel tests reveal a risk of a catastrophic phenomenon (e.g. superstall, a condition at angles beyond the stalling incidence from which it proves difficult or impossible to recover the aeroplane), studies should be made to show that adequate recovery control is available at and sufficiently beyond the stalling incidence to avoid such a phenomenon.

CS 25.207 Stall warning

ED Decision 2016/010/R

(a) Stall warning with sufficient margin to prevent inadvertent stalling with the flaps and landing gear in any normal position must be clear and distinctive to the pilot in straight and turning flight.

(b) The warning must be furnished either through the inherent aerodynamic qualities of the aeroplane or by a device that will give clearly distinguishable indications under expected conditions of flight. However, a visual stall warning device that requires the attention of the crew within the cockpit is not acceptable by itself. If a warning device is used, it must provide a warning in each of the aeroplane configurations prescribed in sub-paragraph (a) of this paragraph at the speed prescribed in sub-paragraphs (c) and (d) of this paragraph. Except for the stall warning prescribed in subparagraph (h)(3)(ii) of this paragraph, the stall warning for flight in icing conditions must be provided by the same means as the stall warning for flight in non-icing conditions. (See AMC 25.207(b).)

(c) When the speed is reduced at rates not exceeding 0.5 m/s2 (one knot per second), stall warning must begin, in each normal configuration, at a speed, VSW, exceeding the speed at which the stall is identified in accordance with CS 25.201(d) by not less than 9.3 km/h (five knots) or five percent CAS, whichever is greater. Once initiated, stall warning must continue until the angle of attack is reduced to approximately that at which stall warning began. (See AMC 25.207(c) and (d)).

(d) In addition to the requirement of subparagraph(c) of this paragraph, when the speed is reduced at rates not exceeding 0.5 m/s2 (one knot per second), in straight flight with engines idling and at the centre-of-gravity position specified in CS 25.103(b)(5), VSW, in each normal configuration, must exceed VSR by not less than 5.6 km/h (three knots) or three percent CAS, whichever is greater. (See AMC 25.207(c) and (d)).

(e) In icing conditions, the stall warning margin in straight and turning flight must be sufficient to allow the pilot to prevent stalling (as defined in CS 25.201(d)) when the pilot starts a recovery manoeuvre not less than three seconds after the onset of stall warning. When demonstrating compliance with this paragraph, the pilot must perform the recovery manoeuvre in the same way as for the airplane in non-icing conditions. Compliance with this requirement must be demonstrated in flight with the speed reduced at rates not exceeding 0.5 m/sec2 (one knot per second), with –

(1) The most critical of the take-off ice and final take-off ice accretions defined in Appendices C and O, as applicable, in accordance with CS 25.21(g), for each configuration used in the take-off phase of flight;

(2) The most critical of the en route ice accretion(s) defined in Appendices C and O, as applicable, in accordance with CS 25.21(g), for the en route configuration;

(3) The most critical of the holding ice accretion(s) defined in Appendices C and O, as applicable, in accordance with CS 25.21(g), for the holding configuration(s);

(4) The most critical of the approach ice accretion(s) defined in Appendices C and O, as applicable, in accordance with CS 25.21(g), for the approach configuration(s); and

(5) The most critical of the landing ice accretion(s) defined in Appendices C and O, as applicable, in accordance with CS 25.21(g), for the landing and go-around configuration(s).

(f) The stall warning margin must be sufficient in both non-icing and icing conditions to allow the pilot to prevent stalling when the pilot starts a recovery manoeuvre not less than one second after the onset of stall warning in slowdown turns with at least 1.5g load factor normal to the flight path and airspeed deceleration rates of at least 1 m/sec2 (2 knots per second), When demonstrating compliance with this paragraph for icing conditions, the pilot must perform the recovery manoeuvre in the same way as for the airplane in non-icing conditions. Compliance with this requirement must be demonstrated in flight with –

(1) The flaps and landing gear in any normal position;

(2) The aeroplane trimmed for straight flight at a speed of 1.3 VSR; and

(3) The power or thrust necessary to maintain level flight at 1.3 VSR.

(g) Stall warning must also be provided in each abnormal configuration of the high lift devices that is likely to be used in flight following system failures (including all configurations covered by Aeroplane Flight Manual procedures).

(h) The following stall warning margin is required for flight in icing conditions before the ice protection system has been activated and is performing its intended function. Compliance must be shown using the most critical of the ice accretion(s) defined in Appendix C, part II(e), and Appendix O, part II(d), as applicable, in accordance with CS 25.21(g). The stall warning margin in straight and turning flight must be sufficient to allow the pilot to prevent stalling without encountering any adverse flight characteristics when:

(1) The speed is reduced at rates not exceeding 0.5 m/sec² (one knot per second);

(2) The pilot performs the recovery manoeuvre in the same way as for flight in non-icing conditions; and

(3) The recovery manoeuvre is started no earlier than:

(i)  One second after the onset of stall warning if stall warning is provided by the same means as for flight in non-icing conditions; or

(ii)  Three seconds after the onset of stall warning if stall warning is provided by a different means than for flight in non-icing conditions.

(i)  In showing compliance with subparagraph (h) of this paragraph, if stall warning is provided by a different means in icing conditions than for non-icing conditions, compliance with CS 25.203 must be shown using the accretion defined in appendix C, part II(e). Compliance with this requirement must be shown using the demonstration prescribed by CS 25.201, except that the deceleration rates of CS 25.201(c)(2) need not be demonstrated.

[Amdt 25/3]

[Amdt 25/7]

[Amdt 25/16]

[Amdt 25/18]

AMC 25.207(b) Stall warning

ED Decision 2003/2/RM

1 A warning which is clear and distinctive to the pilot is one which cannot be misinterpreted or mistaken for any other warning, and which, without being unduly alarming, impresses itself upon the pilot and captures his attention regardless of what other tasks and activities are occupying his attention and commanding his concentration. Where stall warning is to be provided by artificial means, a stick shaker device producing both a tactile and an audible warning is an Acceptable Means of Compliance.

2 Where stall warning is provided by means of a device, compliance with the requirement of CS 25.21(e) should be established by ensuring that the device has a high degree of reliability. One means of complying with this criterion is to provide dual independent systems.

AMC 25.207(c) and (d) Stall warning

ED Decision 2003/2/RM

1 An acceptable method of demonstrating compliance with CS 25.207(c) is to consider stall warning speed margins obtained during stall speed demonstration (CS 25.103) and stall demonstration (CS 25.201(a)) (i.e. bank angle, power and centre of gravity conditions).

In addition, if the stall warning margin is managed by a system (thrust law, bank angle law, …), stall warning speed margin required by CS 25.207(c) should be demonstrated, when the speed is reduced at rates not exceeding 0.5 m/s2 (one knot per second), for the most critical conditions in terms of stall warning margin, without exceeding 40° bank angle or maximum continuous power or thrust during the demonstrations. In the case where the management system increases, by design, the stall warning speed margin from the nominal setting (flight idle, wing level), no additional demonstration needs to be done.

2 The stall warning speed margins required by CS 25.207(c) and (d) must be determined at a constant load factor (i.e. 1g for 207(d)). An acceptable data reduction method is to calculate k = √(CLID/CLSW) where CLID and CLSW are the CL values respectively at the stall identification and at the stall warning activation.

3 If the stall warning required by CS 25.207 is provided by a device (e.g. a stick shaker), the effect of production tolerances on the stall warning system should be considered when evaluating the stall warning margin required by CS 25.207(c) and (d) and the manoeuvre capabilities required by CS 25.143(g).

a. The stall warning margin required by CS 25.207(c) and (d) should be available with the stall warning system set to the most critical setting expected in production. Unless another setting would be provide a lesser margin, the stall warning margin required by CS 25.207(c) should be evaluated assuming the stall warning system is operating at its high angle of attack limit. For aeroplanes equipped with a device that abruptly pushes the nose down at a selected angle-of-attack (e.g. a stick pusher), the stall warning margin required by CS 25.207(c) may be evaluated with both the stall warning and stall identification (e.g. stick pusher) systems at their nominal angle of attack settings unless a lesser margin can result from the various system tolerances.

b. The manoeuvre capabilities required by CS 25.143(g) should be available assuming the stall warning system is operating on its nominal setting. In addition, when the stall warning system is operating at its low angle of attack limit, the manoeuvre capabilities should not be reduced by more than 2 degrees of bank angle from those specified in CS 25.143(g).

c. The stall warning margins and manoeuvre capabilities may be demonstrated by flight testing at the settings specified above for the stall warning and, if applicable, stall identification systems. Alternatively, compliance may be shown by applying adjustments to flight test data obtained at a different system setting.