Specifies requirements for the electroacoustical performance of systems of instruments used to measure sound for the purposes of aeroplane noise certification, and recommends methods by which tests may be made periodically to verify that the performance continues to comply with the requirements given within stated tolerances. The requirements apply to the instruments used to measure the sound produced by jet-or propeller-driven transport-category aeroplanes of maximum certificated takeoff mass over 9 000 kg, or their propulsion systems when installed on a suitable outdoor engine test stand. This publication supersedes IEC 60561.