Text in force at CS25-28: from CS25-18, effective 24 Jun 2016.
(See AMC 25.631) The aeroplane must be designed to assure capability of continued safe flight and landing of the aeroplane after impact with a 4 lb bird when the velocity of the aeroplane (relative to the bird along the aeroplane’s flight path) is equal to VC at sea-level or 0·85 VC at 2438 m (8000 ft), whichever is the more critical. Compliance may be shown by analysis only when based on tests carried out on sufficiently representative structures of similar design.
ED Decision 2016/010/R · Source