Underwater Locator Beacon Detection Ranges for Fuselage Encapsulated Recorders

An acoustic locator beacon was developed and tested in an underwater environment simulating the conditions that might exist when an aircraft crashed into water. The beacons were self-contained, battery powered, and produced a 10 to 20 millisecond pulse of 35-40 kilohertz at a rate of 1 to 4 pulses per second. The locator beacons were designed to be attached to airborne flight data recorders to assist in investigations following a crash. The trash environmental tests were conducted using a section of an aircraft fuselage that still contained the cabin pressure bulkhead. The beacons tested were placed in two different representative locations; (1) inside the cabin pressure area and (2) aft of the pressure bulkhead in the unpressurized area. The fuselage section was lowered into sea water at depths of 50, 100, and 200 feet, off the coast of the Florida Keys. Search runs were made using a motor powered craft equipped with an acoustic locator receiver. The results indicate that the signals of a fuselage encapsulated locator beacon can be detected at reasonable surface distances (up to 3000 yards) and at depths as low as 200 feet.