The need for a backup to GPS as a source of position, navigation and timing (PNT) information has been obvious for years. GPS is key to critical infrastructures and is deeply embedded in aviation's navigation and next-generation surveillance systems. But GPS depends on a weak signal, subject to interference, and could itself become a target, given our growing dependence on the technology. Since a parallel PNT system exists, which could be fairly rapidly and inexpensively developed into a backup for area navigation (RNAV), now is the time to give that alternative due consideration, not to starve or kill it.
A decision on this parallel technology, which has survived solely on congressional support, is scheduled to be made this year. No less a luminary than Prof. Brad Parkinson of Stanford, the "father" of GPS, has singled out this candidate-Loran-in referring to the need for a GPS backup.
Since 1997 Congress has provided $160 million for the modernization of Loran as a possible GPS backup. In their report last month, Homeland Security Appropriation conferees responded strongly to the most recent termination attempt, calling not only for proper procedure and international notification, but for the "names of officials who agreed to the termination." It sounds like Congress is sending a message.
The opposite of GPS, Loran is a low-frequency, relatively high-power, virtually jam-proof, groundwave-based system. The congressional funds, deployed by FAA to the U.S. Coast Guard, have been used to upgrade transmitters and timing equipment, among other things. Little more needs to be done to bring the system up to the standard to support required navigation performance (RNP) 0.3 for non-precision approach (NPA).
As part of FAA's evaluation of Loran-and the potential for an Enhanced Loran (e-Loran) system building on the recent upgrades-the agency supported the development of new "all in view" avionics receivers that can monitor multiple stations simultaneously to greatly improve accuracy. In 2004, Avionics Magazine cited an FAA/USCG report, stating that a further modernized Loran "could satisfy the current NPA, HEA [harbor entrance and approach] and timing/frequency requirements in the United States and could be used to mitigate the operational effects of a disruption in GPS services." (See August 2004, page 50.) Despite the use of the word, "could," the technical risk is regarded as small; it's the political risk that's large.
Avionics Magazine also reported that a GPS/e-Loran receiver, flight tested in 2003, provided accuracies well within the FAA's NPA standards. (See June 2004, page 22.) Although there are currently no FAA Loran standards, the avionics work already performed would shorten this process and preserve the option. Improvements to Loran's ground infrastructure are required: modernization of stations in Alaska, three new stations, aviation-quality integrity monitoring systems and groundwave propagation modeling. But these things are well understood. Megapulse, a major Loran company, estimates that the modernization and recapitalization of the infrastructure would cost about $65 million.
If the U.S. government decides to make a commitment to e-Loran for the sake of a timing backup, however, will the FAA take advantage of e-Loran's potential and develop standards?
Loran is not in the agency's navigation evolution roadmap. FAA's director of navigation services calls it a "tertiary system that does not have a business case from a navigation perspective." FAA's surveillance community seems to feel the same way. At a recent public meeting on automatic dependent surveillance-broadcast (ADS-B), the FAA program office relegated e-Loran to the second tier of backups, expressing doubts about the lack of standards. But until there is a favorable decision, there will be no avionics business case.
Will the community demand it? Officials at the business and general aviation associations don't want to kill Loran, but aren't overly enthusiastic, either. According to the two representatives contacted by Avionics, aviation sees the benefit but doesn't want to get stuck paying the bill.
The best realistic outcome? Continue funding to bring Loran up to e-Loran standards. At that point it's going to be hard for policy makers, not to mention FAA, to ignore. E-Loran looks like GPS, acts like GPS, but will not fail along the same lines.