FAQ n.46186

How to address compliance with 27/29.251 (Vibration)?


Vibrations related CS27/29 requirements are: 

  • CS 2x.251 Vibrations Requirements
  • CS 2x.771(c)  Pilot compartment
  • CS 2x.1321 (f) Arrangement and visibility
  • CS 2x.1193 (a) Cowling and engine compartment covering

They have the same objectives: Prevent the risk of excessive vibration to mitigate the risk of

  • Damaging systems and primary structure, including its detachment,
  • Flutter (coupling),
  • Detrimental effects in handling qualities and controllability,
  • Detachment of cabin/cockpit items of mass.

For compliance with CS 2x.251 vibrations must be addressed at Rotorcraft level and at Assembly/Part level (regardless of its criticality). This can be demonstrated by:

  • Vibration identification by Resonance Assessment Profile (RAP) testing, and
  • Flight tests as needed,
  • In case of significant vibration, fatigue or damage tolerance evaluation may be necessary.
  • Alternatively, when relevant design similarity exists, detailed design review only may be acceptable.

Note 1: care must be taken in the selection of quantitative and/or qualitative vibration evaluation.

Note 2: Flight tests outside of the approved flight envelope might be required.

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