scope:

This Characteristic describes a hand-held microphone for use with airborne radio installations. Characteristic 538B incorporates changes to the older Characteristic 538 (dated March 3, 1972) and serves as a continuation and modification of the original Characteristic.

Microphones of many design variations are in satisfactory airline usage and many others are available; therefore, this Characteristic does not preclude a particu!ar design nor imply that the design outlined herein constitutes the only satisfactory microphone.