“The Safety Board is concerned that, although the United States supports the termination of 121.5-MHz signal processing, there are an estimated 180,000 general aviation 121.5-MHz ELT’s [Emergency Locator Transmitters] in service with no requirement to upgrade to a 406-MHz ELT when the satellite service is terminated in February 2009,” the National Transportation Safety Board (NTSB) warned the Federal Aviation Administration (FAA) in a 7-page letter of 4 September 2007.

The NTSB urged the FAA to upgrade the requirement for ELTs to avoid a great decrease in “the likelihood of finding downed aircraft in a timely manner.” The ELT is activated automatically when the airplane crashes, aiding rescue forces in locating the wreckage.

Other devices, such as automated teller machines and pizza ovens, emit signals in the same frequency range, necessitating a verification of each 121.5-MHz ELT signal. This is not necessary with the stronger, more accurate digital 406-MHz ELT. As the NTSB says, “While a 121.5-MHx position is accurate to within 12-15 nautical miles, a 406-MHz position is accurate to within only 1-3 nautical miles.”

“This equates to search areas of approximately 707-square nautical miles compared with 28-square nautical miles,” the NTSB observed, and the more refined location can expedite rescue and survival of those injured in an air crash.
Famed aviator Steve Fossett, flying a Citabria Super Decathlon, apparently crashed in the vast trackless desert of Nevada September 2; his airplane’s older 121.5-MHz ELT should have been activated, but signals from the device have not been detected and about a dozen Civil Air Patrol airplanes have not been able to spot wreckage of his airplane. The search was called off on 3 October.

Only about 10% of the planes in the U.S., mostly commercial airliners and a smattering of general aviation airplanes, have the new, more powerful transmitters. In its recommendation letter, the NTSB gave a vivid comparison of the difference. A Piper PA-32-300 equipped with the old ELT crashed, and it took until the next day to find the wrecked plane. The pilot died from hypothermia and a heart attack at the hospital, and one of his sons on the flight had a gangrenous leg amputated. In another case involving a Cessna Citation 560, equipped with the newer ELT, crashed and was located within 45 minutes (although everybody aboard was killed).