AMC
25.251(e) Vibration and Buffeting in Cruising Flight
ED Decision 2003/2/RM
1 Probable Inadvertent Excursions beyond the Buffet Boundary
1.1 CS 25.251(e) states that probable inadvertent excursions beyond the buffet onset boundary may not result in unsafe conditions.
1.2 An acceptable means of compliance with this requirement is to demonstrate by means of flight tests beyond the buffet onset boundary that hazardous conditions will not be encountered within the permitted manoeuvring envelope (as defined by CS 25.337) without adequate prior warning being given by severe buffeting or high stick forces.
1.3 Buffet onset is the lowest level of buffet intensity consistently apparent to the flight crew during normal acceleration demonstrations in smooth air conditions.
1.4 In flight tests beyond the buffet onset boundary to satisfy paragraph 1.2, the load factor should be increased until either –
a. The level of buffet becomes sufficient to provide an obvious warning to the pilot which is a strong deterrent to further application of load factor; or
b. Further increase of load factor requires a stick force in excess of 445 N (100 lbf), or is impossible because of the limitations of the control system; or
c. The positive limit manoeuvring load factor established in compliance with CS 25.337(b) is achieved.
1.5 Within the range of load factors defined in paragraph 1.4 no hazardous conditions (such as hazardous involuntary changes of pitch or roll attitude, engine or systems malfunctioning which require urgent corrective action by the flight crew, or difficulty in reading the instruments or controlling the aeroplane) should be encountered.
2 Range of Load Factor for Normal Operations
2.1 CS 25.251(e) requires that the envelopes of load factor, speed, altitude and weight must provide a sufficient range of speeds and load factors for normal operations.
2.2 An acceptable means of compliance with the requirement is to establish the maximum altitude at which it is possible to achieve a positive normal acceleration increment of 0·3 g without exceeding the buffet onset boundary.
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