Plane & Pilot
Thursday, January 1, 2004

Emergency Locator Transmitters


How they work and why things are about to change



Stated simply, EPIRB/GPS can pinpoint position of any signal within a 600-foot diameter circle anywhere on Earth, reducing the search area of a standard ELT by a factor of nearly 50.

The sequence of events that initiates a search with a 406 EPIRB is fairly simple. After a satellite receives an EPIRB transmission, it relays all information in the encoded digital signal to a ground station. If there's no ground station in view, the satellite saves the message to memory and downloads it to the next station available.

The ground station then calculates the position of the EPIRB, refining the position with each subsequent pass. After processing, the ground station transmits the alert to the U.S. Mission Control Center (USMCC) in Maryland. USMCC alerts the AFRCC, where analysts attempt to determine the aircraft's disposition. If AFRCC is unable to verify the aircraft is safely on the ground, they launch a search and rescue mission. For aircraft down off coastal waters, the U.S. Coast Guard will be alerted. Most of these steps are made considerably more difficult or impossible with standard ELTs, as there's usually no independent way of knowing the identity of the pilot and aircraft.

For all the reasons above, the standard ELT frequency of 121.5/243 MHz will be phased out on February 1, 2009, and all subsequent SAR beacons will be confined to 406 MHz.

EPIRBs come in a variety of styles, shapes, sizes and weights, from hard mount units to portable cigarette-package-size PLBs (personal locator beacons), designed to be clipped to a belt. While there are dedicated aviation EPIRBs, marine units serve the same purpose and (perhaps surprisingly) cost about the same. Prices range from $500 to more than $2,000.

That's not cheap in contrast to the relatively low cost of the old ELTs, but it's a worthwhile investment if it only saves your life once.



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