CS 25.251 Vibration and buffeting

Large Aeroplanes (CS-25) · CS-25 · EAR revision 26 Jan 2023

IRImplementing rule

CS 25.251Vibration and buffeting

(See AMC 25.251)

(a)The aeroplane must be demonstrated in flight to be free from any vibration and buffeting that would prevent continued safe flight in any likely operating condition.

(b)Each part of the aeroplane must be demonstrated in flight to be free from excessive vibration under any appropriate speed and power conditions up to VDF/MDF. The maximum speeds shown must be used in establishing the operating limitations of the aeroplane in accordance with CS 25.1505.

(c)Except as provided in sub-paragraph (d) of this paragraph, there may be no buffeting condition, in normal flight, including configuration changes during cruise, severe enough to interfere with the control of the aeroplane, to cause excessive fatigue to the crew, or to cause structural damage. Stall warning buffeting within these limits is allowable.

(d)There may be no perceptible buffeting condition in the cruise configuration in straight flight at any speed up to VMO/MMO, except that the stall warning buffeting is allowable.

(e)For an aeroplane with MD greater than 0·6 or with a maximum operating altitude greater than 7620 m (25,000 ft), the positive manoeuvring load factors at which the onset of perceptible buffeting occurs must be determined with the aeroplane in the cruise configuration for the ranges of airspeed or Mach number, weight, and altitude for which the aeroplane is to be certificated. The envelopes of load factor, speed, altitude, and weight must provide a sufficient range of speeds and load factors for normal operations. Probable inadvertent excursions beyond the boundaries of the buffet onset envelopes may not result in unsafe conditions. (See AMC 25.251(e).)

[Amdt 25/1]

[Amdt 25/18]

IR · CS 25.251 — CS-25 · ED Decision 2016/010/R · CS-25 Easy Access Rules · EAR revision 26 Jan 2023

AMCAcceptable means of compliance

AMC 25.251(e)Vibration and Buffeting in Cruising Flight

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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.

AMC · AMC 25.251(e) — CS-25 · ED Decision 2003/2/RM · CS-25 Easy Access Rules · EAR revision 26 Jan 2023

All rules in SUBPART B – FLIGHT

Consolidated from the EASA Easy Access Rules (revision 26 Jan 2023, extracted 17 Aug 2026) for convenience. Not the official publication — verify against the Official Journal of the European Union and the EASA publications before operational use.

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