1 The investigation should cover the complete range, for which certification is required, of aeroplane speeds, attitudes, altitudes and engine operating conditions including reverse thrust, and of steady and transient conditions on the ground and in flight, including crosswinds, rotation, yaw and stall. Non-critical conditions of operation which need not be considered should be agreed with the Agency. 2 If the airflow conditions at the engine air intake can be affected by the operating conditions of an adjacent engine, the investigation should include an exploration of the effects of running the adjacent engine at the same and at different conditions over the whole range of engine operating conditions, including reverse thrust. An investigation of the effect of malfunctioning of an adjacent engine should also be included. 3 Compliance with the requirement may include any suitable one or combination of the following methods; as agreed with the Agency. a. Demonstration that the variations in engine inlet airflow distortion over the range defined in 1 are within the limits established for the particular engine type. b. An investigation of blade vibration characteristics by the method and of the scope indicated in CS-E 650 and AMC E 650 (except that Maximum Take-off rpm need not be exceeded) carried out on – i A representative installation on the ground using test equipment where the actual conditions of operation in the aeroplane are reproduced, or ii A representative aeroplane on the ground and in flight as appropriate to the conditions being investigated. c. The completion of sufficient flying with representative installations prior to certification such as to demonstrate that the vibration levels are satisfactory. d. Any other method acceptable to the Agency.