Key: EPIRB: Emergency position indicating radio beacon ELT: Emergency locator transmitter PLB: Personal locator beacon SAR: Search and rescue SAR GOES MSG COSPAS SARSAT INSAT SAR Local user terminal (LUT) Mission control center (MCC) Rescue coordination center (RCC) Distressed vessel Distressed aircraft GEO Satellites LEO Satellites PLB EPIRB ELT 406 MHz 406 MHz 406 MHz 406 MHz 406 MHz Downlink Downlink Figure 11-148.  The basic operating components of the satellite-based COSPAS-SARSAT rescue system of which aircraft ELTs are a part.  Being in the low frequency range, the LORAN transmissions  travel long distances and provide good coverage from a small  number of stations.  Precisely-timed, synchronized pulse signals are transmitted  from the towers in a chain. The LORAN receiver measures  the time to receive the pulses from the master tower and two  other towers in the chain. It calculates the aircraft’s position  based on the intersection of parabolic curves representing  elapsed signal times from each of these known points. The accuracy and proliferation of GPS navigation has  caused the U.S. Government to cease support for the  LORAN navigation system citing redundancy and expense  of operating the towers as reasons. The LORAN chain in  the Aleutian Island shared with Russia is the only LORAN  chain at the time of printing of this handbook which had not  yet been given a date for closure. Panel-mounted LORAN  navigation units will likely be removed and replaced by GPS  units in aircraft that have not already done so.  [Figure 11-151]  11-68