After a light plane with two U.S. congressmen on board went down in 1972 and could not be found,[REF] the U.S. began requiring all aircraft to carry an Emergency Locator Transmitter (ELT) that would turn on automatically in the event of a crash.
Maritime practice has shifted from rescue radios on 500 kHz distress frequency (which is no longer officially monitored) to the Global Maritime Distress Safety System, which includes use of the Cospas-Sarsat system and other measures, including radar transponders and hand-held marine VHF radios.