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 = √(C_LID/C_LSW) where C_LID and C_LSW are the C_L 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.