AMC 25.145(a) Longitudinal control - Control near the stall

ED Decision 2018/005/R

1       CS 25.145(a) requires that there be adequate longitudinal control to promptly pitch the aeroplane nose down from at or near the stall to return to the original trim speed. The intent is to ensure sufficient pitch control for a prompt recovery if the aeroplane is inadvertently slowed to the point of the stall. Although this requirement must be met with engine thrust or power off and at go-around setting, there is no intention to require stall demonstrations at engine thrusts or powers above that specified in CS 25.201(a)(2). Instead of performing a full stall at go-around thrust or power setting, compliance may be assessed by demonstrating sufficient static longitudinal stability and nose down control margin when the deceleration is ended at least one second past stall warning during a 0.5 m/s² (one knot per second) deceleration. The static longitudinal stability during the manoeuvre and the nose down control power remaining at the end of the manoeuvre must be sufficient to assure compliance with the requirement.

2       The aeroplane should be trimmed at the speed for each configuration as prescribed in CS 25.103(b)(6). The aeroplane should then be decelerated at 0.5 m/s² (1 knot per second) with wings level. For tests at idle thrust or power, it should be demonstrated that the nose can be pitched down from any speed between the trim speed and the stall. Typically, the most critical point is at the stall when in stall buffet. The rate of speed increase during the recovery should be adequate to promptly return to the trim point. Data from the stall characteristics test can be used to evaluate this capability at the stall. For tests at go-around thrust or power setting, the manoeuvre need not be continued for more than one second beyond the onset of stall warning. However, the static longitudinal stability characteristics during the manoeuvre and the nose down control power remaining at the end of the manoeuvre must be sufficient to assure that a prompt recovery to the trim speed could be attained if the aeroplane is slowed to the point of stall.

3        For aeroplanes with an automatic pitch trim function (either in manual control or automatic mode), the nose-up pitch trim travel should be limited before or at stall warning activation (or stall buffet onset, or before reaching the angle-of-attack (AOA) limit if a high AOA limiting function is installed), in order to prevent an excessive nose-up pitch trim position and ensure that it is possible to command a prompt pitch down of the aeroplane to recover control.

The applicant should demonstrate this feature during flight testing or by using a validated simulator.

Note 1: the behaviour of the automatic pitch trim function in degraded flight control laws should be evaluated under CS 25.1309 and CS 25.671.

Note 2: the applicant may account for certain flight phases where this limit is not appropriate, and provide a rationale that supports these exceptions to EASA for consideration.

[Amdt No: 25/21]