1.1 This International Standard specifies laboratory conditions for testing the ability of equipment for subsonic and supersonic civil aircraft to withstand the effects of acoustic vibration. Two types of tests are specified : tests for the functioning of the equipment, and tests for its acoustic endurance. The tests for the functioning of the equipment are carried out both during equipment development and for certification. The tests for acoustic endurance are usually carried out in order to find structural defects during equipment development. 1.1.1 The tests for the functioning of the equipment may be carried out in accordance with one of the two alternative methods. — wide band noise test — harmonic sound test. The tests for acoustic endurance are carried out using the wide band noise method. 1.1.2 The selection of the test severity grade is made by the user in accordance with one of the following two procedures : a) If measurements of sound pressure levels at the location where the equipment is to be installed are available for in-flight conditions or can be calculated, they can be used to determine test sound pressure levels by a method proposed in this International Standard. This is referred to as procedure "A" (see 4.4.1, 5.2.1, and the annex). b) If such measurements are not available or the user does not wish to use method A, the test levels may be obtained from this International Standard on the basis of the type of aircraft in which the equipment is to be installed and the location of the equipment in the aircraft with respect to the noise sources. In this method, which will be referred to as procedure "B", the test sound pressure level can be determined by means of the tables and formulae given in this International Standard (see 4.4.2; 5.2.2, and the annex). 1.2 The tests are intended to be applied to equipment sensitive to acoustic vibration. The necessity for functioning and endurance tests, the use of the wide band noise method or harmonic sound method, and the applicable test sound pressure level shall be specified in the relevant equipment specifications. 1.2.1 The equipment located in aircraft, regions where overall sound pressure levels are less than 125 dB will not normally require testing in acoustic vibration environments.