CS 25.253 High-speed characteristics

An acceptable method of demonstrating compliance with CS 25.253(a)(4) is as follows: 1 Establish a steady 20° banked turn at a speed close to VDF/MDF limited to the extent necessary to accomplish the following manoeuvre and recovery without exceeding VDF/MDF. Using lateral control alone, it should be demonstrated that the aeroplane can be rolled to 20° bank angle in the other direction in not more than 8 seconds. The demonstration should be made in the most adverse direction. The manoeuvre may be unchecked. 2 For aeroplanes that exhibit an adverse effect on roll rate when rudder is used, it should also be demonstrated that use of rudder in a conventional manner will not result in a roll capability significantly below that specified above. 3 Conditions for 1 and 2: Wing-flaps retracted. Speedbrakes retracted and extended. Landing gear retracted. Trim. The aeroplane trimmed for straight flight at VMO/MMO. The trimming controls should not be moved during the manoeuvre. Power:

(i)All engines operating at the power required to maintain level flight at VMO/MMO, except that maximum continuous power need not be exceeded; and

(ii)if the effect of power is significant, with the throttles closed.

Extension of Speedbrakes. The following guidance is provided to clarify the meaning of the words “the available range of movements of the pilot’s control” in CS 25.253(a)(5) and to provide guidance for demonstrating compliance with this requirement. Normally, the available range of movements of the pilot’s control includes the full physical range of movements of the speedbrake control (i.e., from stop to stop). Under some circumstances, however, the available range of the pilot’s control may be restricted to a lesser range associated with in-flight use of the speedbrakes. A means to limit the available range of movement to an in-flight range may be acceptable if it provides an unmistakable tactile cue to the pilot when the control reaches the maximum allowable in-flight position, and compliance with CS 25.697(b) is shown for positions beyond the in-flight range. Additionally, the applicant's recommended procedures and training must be consistent with the intent to limit the in-flight range of movements of the speedbrake control. CS 25.697(b) requires that lift and drag devices intended for ground operation only must have means to prevent the inadvertent operation of their controls in flight if that operation could be hazardous. If speedbrake operation is limited to an in-flight range, operation beyond the in-flight range of available movement of the speedbrake control must be shown to be not hazardous. Two examples of acceptable unmistakable tactile cues for limiting the in-flight range are designs incorporating either a gate, or incorporating both a detent and a substantial increase in force to move the control beyond the detent. It is not an acceptable means of compliance to restrict the use of, or available range of, the pilot’s control solely by means of an aeroplane Flight Manual limitation or procedural means. The effect of extension of speedbrakes may be evaluated during other high speed testing and during the development of emergency descent procedures. It may be possible to infer compliance with CS 25.253(a)(5) by means of this testing. To aid in determining compliance with the qualitative requirements of this rule, the following quantitative values may be used as a generally acceptable means of compliance. A load factor should be regarded as excessive if it exceeds 2.0. A nose-down pitching moment may be regarded as small if it necessitates an incremental control force of less than 89 N (20 lbf) to maintain 1g flight. These values may not be appropriate for all aeroplanes, and depend on the characteristics of the particular aeroplane design in high speed flight. Other means of compliance may be acceptable, provided that the Agency finds that compliance has been shown to the qualitative requirements specified in CS 25.253(a)(5).