Industry sends DOT mixed message on GPS backup system
- By Bob Brewin
- Feb 15, 2007
DOT Loran Comment Web Site
The Air Transport Association (ATA) told the Transportation Department it backed a shutdown of the terrestrial long-range radio navigation (Loran) system, while Boeing said it recognized the potential for Loran to provide a robust backup navigation capability for the satellite-based Global Positioning System.
DOT asked for public comment early last month on whether to shut down Loran or develop a fully deployed enhanced Loran (eLoran) system that could serve as a GPS backup. Major organizations such as the Air Transport Association of America (ATA), Boeing, Airbus and Sprint Nextel weighed in with comments last week. DOT has extended the deadline for comments from Feb. 7 to March 30.
ATA, which represents the U.S. airline industry, told DOT that none of its member airlines uses Loran for Positioning, Navigation and Timing (PNT). It views eLoran as an immature technology that will require extensive development and testing. ATA said it supports decommissioning the existing Loran system, adding that none of its member airlines is considering using eLoran.
Loran receivers help users determine their locations based on the time interval of signals received from different transmitters. ELoran stations transmit a data channel with as many as 16 messages, including station identification, absolute time and differential correction messages, and are as accurate as GPS, according to a recent study done in the United Kingdom.
Boeing told DOT that equipping commercial airliners with Loran equipment would be a “very expensive proposition,” but added that Loran could provide alternative navigation capability in North America, much of Europe and coastal regions in Asia. Unlike the Federal Aviation Administration’s Wide Area Augmentation System, Loran is a “truly independent” source of PNT information and is difficult to jam or spoof, Boeing said.
Airbus, a European commercial aircraft manufacturer, said it does not support the use of Loran as a supplement to GPS for aviation use, and agreed with ATA and Boeing that terrestrial navigation aids such as Distance Measuring Equipment and very high-frequency omnidirectional range could serve well as backups to GPS.
Sprint Nextel said it relies on GPS and Loran for timing signals to operate its network. The company told DOT that if the agency shuts down the Loran system, it should wait until the eLoran system is fully operational. The Coast Guard has spent $160 million modernizing Loran since 1997, and a white paper prepared for the FAA estimates the system could be fully deployed in the U.S. for an additional $24 million to $27 million.
Sprint Nextel said GPS is susceptible to interference, spoofing and jamming because of its low power signals and high frequency, adding that it also does not work well indoors. Loran uses a high-powered, low-frequency signal and could provide a complementary, redundant signal to GPS not subject to the same type of failure, that company said. ELoran has timing capabilities that can meet the synchronization requirements of its Code Division Multiple Access cellular network, Sprint Nextel added.
The American Pilots Association, which represents pilots of ocean-going vessels in U.S. ports and waterways, said the Coast Guard Differential GPS (DGPS) network, which provides highly accurate navigation signals used by association members, can be blocked, jammed or corrupted. Development of eLoran would provide “benefits and values far in excess of its costs,” that association said.
The organization said in its filing with DOT that a loss of accurate PNT information due to a disruption of DGPS “would be far more dangerous and potentially crippling to our nation than many of the contingencies that other Coast Guard programs are designed to prevent.”
“The safe and efficient movement of waterborne commerce on which our country depends provides reason enough to justify the modest cost of a fully developed eLoran system,” the association added.
The European Institutes of Navigation said in its filing with DOT that the Loran system should not be shut down. It supports deployment of eLoran because it can provide accuracy, integrity and continuity needed for a backup to GPS, that group said.
The General Lighthouse Authorities of the United Kingdom and Ireland said it does not consider GPS adequate for future navigation and timing requirements, and views eLoran as the only candidate to support e-navigation in high traffic density, restricted waters, particularly sensitive sea areas and environmental risk areas.
Trinity House, a United Kingdom organization that provides marine aids to navigation in England, Wales, the Channel Islands and Gibraltar, issued a request for proposals for an eLoran system in January.