MIL-L-25971B, MILITARY SPECIFICATION: LIGHT, AIRPORT TRAFFIC CONTROL, SDU-4/U (29-MAY-1967) [SUPERSEDED BY MIL-DTL-25971C]

MIL-L-25971B, MILITARY SPECIFICATION: LIGHT, AIRPORT TRAFFIC CONTROL, SDU-4/U (29-MAY-1967) [SUPERSEDED BY MIL-DTL-25971C]., This specification covers one type of airport traffic control light designated SDU-4/U. The lights are intended to be used in permanent or mobile air-traffic control towers to control air traffic in the event radio transmission is not available.