An emergency location transmitter is a radio transmitter attached to the aircraft structure used as an alerting and locating aid for survival purposes. It operates from its own power source on 121.5 MHz and 243.0 MHz and can be manually or automatically activated to transmit a distress signal to a satellite. ELTs that activate automatically use a "G-Switch" (gravity switch) that triggers the ELT when it senses that a crash has occurred. An ELT makes it easier for rescue teams to get the exact location of a downed aircraft. The FAA requires all aircraft to have an emergency location transmitter. Section 91.207 of the Federal Aviation Regulations, as well as Part 121 operators and operations governed by Part 135, states that no person may operate a U.S. registered civil aircraft unless an approved automatic type emergency locator transmitter is attached to the aircraft. Similar regulations are established by aviation authorities throughout the world. The FAA Technical Standard Orders state the minimum performance standard that an ELT operating at 406.0 Megahertz must meet, and determines the requirement for the aircraft owner to register the digital message programmed into the ELT with Cospas/Sarsat. TSO C-126 approved ELTs will also transmit on 121.5 MHz frequency, but satellite alerting of the 121.5 MHz distress signal will be discontinued after February 1, 2009.