Report could give loran new life as GPS backup

 - March 27, 2007, 12:39 PM

Loran advocates believe they are on a roll. A number of events that transpired so far this year, coupled with a government report on loran due soon, have boosted their confidence that this could be the year when their system finally gains its long-due recognition.

The FAA has never been overly enthusiastic about loran, citing its sometimes erratic IFR performance, its lack of failure warnings and its poor accuracy compared with GPS, which the agency predicted would become the nation’s “sole means” of navigation, rendering all other navaids obsolete. In 1994 the agency announced that loran would be shut down in 2000.

But Congress overrode that ruling, and since 1998 it has included funding for loran system upgrades and further development. In 2001,  funding went from the previous year’s $10 million to $25 million, and has since remained at similar levels each year. The legislators were persuaded, after a DOT report and 9/11, that modernized loran had the potential to become the required backup to GPS. In January, Congress again authorized loran funding, setting aside $22.5 million for such use in fiscal year 2005, and bringing its total authorization since 1998 to almost $100 million.

Most of these funds have gone toward upgrading the nationwide loran transmitter network, converting old tube-type equipment to new solid-state units and improving its precise timing capabilities, although the system was already one of just three–the other two being GPS and laboratory atomic clocks–that met the nation’s highest Stratum 1 timekeeping standards.

Other funds have supported tests of new loran receiver concepts. Chief among these has been the development of “all in view” receivers that use signals from every loran transmitter across the country, rather than just the four stations of a regional “chain.” FAA Technical Center researchers have reported that the all-in-view units continuously track signals from between 20 and 30 transmitters for maximum accuracy and redundancy. Tests of this concept have been conducted by several organizations, including Rockwell Collins, which modified a multimode ILS/GPS/MLS landing guidance receiver by substituting loran for the MLS component. Here, the GPS continuously kept the loran within its own tight accuracy tolerances, and under simulated GPS failures the enhanced loran automatically maintained comparable accuracy.

In January at the U.S. Institute of Navigation’s Annual Technical Symposium, Rockwell Collins described further tests of the concept, this time to assess how well an all-in-view loran performed when integrated with a low-cost inertial measurement unit in the event of GPS failure. Results showed that loran followed the GPS ground track within “a few meters.”

In recognition of these major changes, the loran community has also upgraded the system’s name. It’s no longer referred to as loran-C, since that describes the “old” system. Today’s preferred name is E-loran, although plain loran is still acceptable.

Another announcement that buoyed the loran community’s spirits came in the February report of a high-level federal government radionavigation systems task force, which was charged in December 2001 by Transportation Secretary Norman Mineta with recommending an economical investment strategy for the future mix of navigation systems. Particular emphasis was to be placed on multimodal–meaning land, sea and air–applications and national security benefits. The report identified loran as “the only available cross-modal navigation backup to GPS.”

But the major input to loran’s possible recognition as a future complement to GPS is expected late this month, when the report of a three-year, multi-agency, industry and university loran evaluation team study will be submitted to the Departments of Transportation and Homeland Security.

This report will be an assessment of the capabilities of the new E-loran and will analyze the system’s accuracy, integrity, availability and continuity, along with its ability to meet RNP 0.3 operation throughout the continental U.S., which is important for GA. While results of this study are being closely held, informed sources have told AIN that its overall conclusions are regarded as favorable for loran.