Figure 11-147.  A satellite weather receiver and antenna enable display of real-time textual and graphic weather information beyond that  of airborne weather radar. A handheld GPS can also be equipped with these capabilities. A built-in multifunctional display with satellite  weather overlays and navigation information can be found on many aircraft.  Long Range Aid to Navigation System (LORAN) 11-67 Long range aid to navigation system (LORAN) is a type of  RNAV that is no longer available in the United States. It was  developed during World War II, and the most recent edition,  LORAN-C, has been very useful and accurate to aviators as  well as maritime sailors. LORAN uses radio wave pulses  from a series of towers and an on-board receiver/computer  to positively locate an aircraft amid the tower network. There  are twelve LORAN transmitter tower “chains” constructed  across North America. Each chain has a master transmitter  tower and a handful of secondary towers. All broadcasts  from the transmitters are at the same frequency, 100 KHz.  Therefore, a LORAN receiver does not need to be tuned.  The use of a 406 MHz ELT has not been mandated by the  FAA. An older 121.5 MHz ELT satisfies the requirements  of FAR Part 91.207 in all except new aircraft. Thousands of  aircraft registered in the United States remain equipped with  ELTs that transmit a .75 watt analog 121.5 MHz emergency  signal when activated. The 121.5 MHz frequency is still an  active emergency frequency and is monitored by over-flying  aircraft and control towers.  Modern ELTs may also transmit a signal on 121.5 MHz. This  is an analog transmission that can be used for homing. Prior  to 2009, 121.5 MHz was a worldwide emergency frequency  monitored by the CORPAS-SARSAT satellites. However, it  has been replaced by the 406 MHz standard. Transmission on  121.5 MHz are no longer received and relayed via satellite. ELTs with automatic G-force activation mounted in  aircraft are easily removable. They often contain a portable  antenna so that crash victims may leave the site and carry  the operating ELT with them. A flight deck mounted panel  is required to alert the pilot if the ELT is activated. It also  allows the ELT to be armed, tested, and manually activated  if needed.  [Figure 11-150] It must be noted that older 121.5 MHz analog signal ELTs  often also transmit an emergency signal on a frequency of  243.0 MHz. This has long been the military emergency  frequency. Its use is being phased out in favor of digital ELT  signals and satellite monitoring. Improvements in coverage,  location accuracy, identification of false alerts, and shortened  response times are so significant with 406 MHz ELTs, they  are currently the service standard worldwide.  Use of Doppler technology enables the origin of the 406  MHz ELT signal to be calculated within 2 to 5 kilometers.  Second generation 406 MHz ELT digital signals are loaded  with GPS location coordinates from a receiver inside the  ELT unit or integrated from an outside unit. This reduces  the location accuracy of the crash site to within 100 meters.  The digital signal is also loaded with unique registration  information. It identifies the aircraft, the owner, and contact  information, etc. When a signal is received, this is used to  immediately research the validity of the alert to ensure it is  a true emergency transmission so that rescue resources are  not deployed needlessly. Technicians are required to perform an inspection/test of  121.5 MHz ELTs within 12 months of the previous one and  inspect for the same integrity as required for the 406 MHz  ELTs mentioned above. However, older ELTs often lack the  built-in test circuitry of modern ELTs certified to TSO C-126.  Therefore, a true operational test may include activating  the signal. This can be done by removing the antenna and  installing a dummy load. Any activation of an ELT signal is  required to only be done between the top of each hour and 5  minutes after the hour. The duration of activation must be no  longer than three audible sweeps. Contact of the local control  tower or flight service station before testing is recommended. 