Pinger Locator System to listen for TWA Flight 800 flight data recorders. This Pinger Locator System is part of the Navy equipment being transported to the crash site of TWA Flight 800 to be used by the Navy in an attempt to locate the aircraft's flight data recorders more commonly known as Black Boxes. The PLS is a highly sensitive, underwater microphone which is towed in the water to listen for the pingers located on the flight data recorders. SHARE: Download: Full Size (0.05 MB) Credit: VIRIN: 589718-H-IKP76-400.jpg Photo Gallery