South Korea has been subject to annual GPS jamming attacks by its North Korean neighbor since 2010. Over that period, jamming has extended over longer periods, with the longest being a continuous 16-day attack, employing various frequencies, techniques and signal strengths. As the jamming periods increased each year, they affected more and more GPS users. Last year, South Korean officials estimated that 1,016 aircraft lost GPS signals, as did 254 ships and a large number of cellphone towers.

The jamming seriously affected South Korea’s substantial merchant fleet and its key trans-Pacific export trade to the U.S., for which GPS has become a standard navaid. And while aircraft arrivals and departures to and from South Korea are more numerous than shipping movements, they would have been much less affected since most long-range aircraft could fall back on theinertial systems they already carried, supported by Asia’s longstanding VOR/DME network, which also serves regional aircraft operations.

Another Chance for Loran

But the North Korean GPS jamming attacks did underscore the vulnerability of the very low-powered GPS signals, and South Korea recently announced a nationwide eLoran navigation project under which the entire country will be covered by the new system in 2016, with 20-meter position accuracy.

The eLoran system is the 21st-century successor to the old loran-C. Operationally, it retains the very low frequency 200 kHz signals of its loran-C predecessor, which give it its powerful and unjammable long-range, ground-hugging signals that extend from the surface to well above jet altitudes and are not blocked by intervening high ground. Explained Charles Schue, president of Chesapeake, Va.-based UrsaNav, a developer of eLoran technology, “eLoran then adds several new benefits.” First, it no longer uses loran-C’s regional groupings of Master and Secondary transmitting stations, and replaces them with widely separated stations operating independently to cover very large areas, such as, say, the continental U.S., and where individual eLoran stations would function in much the same way as individual GPS satellites.

Second, he explained, like GPS, an eLoran receiver then continuously tracks the “all-in-view” eLoran signals, and selects those having the best signal quality and most favorable fix geometry. Third, new antenna technology has eliminated the precipitation static that seriously hampered the old loran-C signals. Finally, each eLoran station has an advanced data transmission channel that offers a number of potential applications.

So is there an airborne eLoran receiver in UrsaNav’s future? “Potentially, but not yet,” said Schue, cautiously. “The airborne market will undoubtedly increase, but it is still quite small. However, the work that UrsaNav is doing in several other eLoran applications, plus the work under way in the UK, France and elsewhere, when coupled with the continuing worldwide threat of GPS interference and jamming, could bring airborne eLoran closer than we might expect.”

What would an aircraft eLoran look like? Certainly, it would look totally unlike the previous bulky loran-C units. Schue declined to speculate on the question, but when the FAA’s Atlantic City Technical Center ran tests of eLoran several years ago, the center’s engineers envisioned that it could be accommodated on a small circuit board–perhaps even within a GPS receiver–where it would operate entirely automatically, without the need for pilot controls. That is, it would continuously track all eLoran transmitters throughout the flight and, as soon as GPS interference appeared, its position data would be switched to the FMS, with appropriate crew alerts. As soon as the GPS interference ended, the FMS would switch back to GPS, and the eLoran would revert to its continuous monitoring role.