CS 25.145 Longitudinal control

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]

Where high lift devices are being retracted and where large and rapid changes in maximum lift occur as a result of movement of high-lift devices, some reduction in the margin above the stall may be accepted.

The presence of gated positions on the flap control does not affect the requirement to demonstrate full flap extensions and retractions without changing the trim control.

If gates are provided, CS 25.145(e) requires the first gate from the maximum landing position to be located at a position corresponding to a go-around configuration. If there are multiple go-around configurations, the following criteria should be considered when selecting the location of the gate: a. The expected relative frequency of use of the available go-around configurations. b. The effects of selecting the incorrect high-lift device control position. c. The potential for the pilot to select the incorrect control position, considering the likely situations for use of the different go-around positions. d. The extent to which the gate(s) aid the pilot in quickly and accurately selecting the correct position of the high-lift devices.

1.CS 25.145(f)(1) requires there to be adequate longitudinal control to promptly pitch the aeroplane (nose down and up) and adequate speed control in order to follow or maintain the targeted trajectory during the complete manoeuvre from any approved approach and landing configuration to a go-around, transition to the next flight phase and level off at the desired altitude. The objective is to assess, in particular, the combined effects of a thrust or power application and a nose-up trim pitching moment. The applicant should perform the evaluation throughout the range of thrust-to-weight ratios to be certified. This range should include, in particular, the highest thrust-to-weight ratio for the all-engines-operating condition, with the aeroplane at its minimum landing weight, all engines operating and the thrust or power at the go-around setting. The evaluation should show adequate: pitch control (i.e. no risk of excessive pitch rate or attitude, maintaining an adequate stall margin throughout the manoeuvre, no excessive overshoot of the level-off altitude), and speed control (i.e. no risk of speed instability or exceedance of VFE with the wing-flaps extended and VLE with the landing gear extended). Refer also to AMC No. 1 to CS 25.1329, Section 14.1.3.3, which provides guidance related to the demonstration of the flight guidance system go-around mode.

2.The applicant shall evaluate reasonably expected variations in service from the established approach, landing and go-around procedures and ensure that they do not result in unsafe flight characteristics during a go-around. It is expected that these variations may include: a) non-stabilised speed conditions prior to the initiation of a go-around (e.g. approach speed - 5 kt), and b) adverse pitch trim positions: i) In manual mode with a manual pitch trim, a pitch trim positioned for the approach or landing configuration, and kept at this position during the go-around phase; and ii) in autopilot or manual mode with an automatic pitch trim function: the most adverse position that can be sustained by the autopilot or automatic pitch trim function, limited to the available protecting/limiting features or alert (if credit can be taken for it). The applicant should perform these demonstrations by conducting go-around manoeuvres in flight or during simulator test programmes.

[Amdt 25/21]