Plane & Pilot
Tuesday, July 26, 2011

Should We Rely On GPS?


Is GPS too good to be true?


I'm one of those weird folks who bought a semi-sophisticated LORAN C receiver in the 1980s, a multichain ARNAV FMS5000, and it's still mounted on the panel of my Mooney. Fortunately, the FMS5000 also picks up GPS signals, so it serves as a backup to my Garmin 430 and 696. (When LORAN was up and running, the discriminator circuitry in the ARNAV unit evaluated the integrity of the GPS and LORAN signals and annunciated the system in use with a small "G" or a small "L." Contrary to what you might imagine, there were instances when the "L" was displayed for long periods of time.)

In some respects, comparing the old LORAN C to GPS is a little like contrasting a VW Beetle to a Porsche Panamera. Despite its antediluvian roots, however, LORAN C delivered nearly the same accuracy and was perhaps less susceptible to interference.

As many readers may remember, a decision was made that LORAN C be shut down in early 2009, suggesting that GPS had relegated LORAN to obsolescence. This allowed the U.S. Coast Guard to spend LORAN's annual $36 million on something else. It also effectively killed LORAN and destroyed any possibility of using it as a backup.

What no one mentioned was that we had already spent $160 million to upgrade the old LORAN C system to more modern eLORAN, an even more accurate and reliable navigation aid, and that project was about half complete. That $160 million was a total write-off.

And, oh yeah, the very act of decommissioning LORAN was scheduled to cost probably another $200-$250 million. At $36 million/year, we could have had another six years of LORAN C backup to GPS for the same price. As my ARNAV unit has so capably demonstrated for 18 years, it's no major engineering feat to incorporate both technologies in the same panel-mounted receiver.

That's all the more disturbing, since LORAN was equal to GPS in some respects, and we now have no precision navigation system to back up GPS in the event of a terrorist attack. The LORAN signal was tough to attenuate. It penetrated most buildings, double-canopy rain forests and urban and natural canyons, and the timing signal was just as accurate as GPS. LORAN used terrestrial rather than space-borne atomic clocks that actually tended to be slightly more accurate (one second every 6 million years?).

But of course, that's all academic now, as the promise of eLORAN is gone for good. For whatever it's worth, I'm still one of the world's strongest supporters of GPS. My Garmin 696 is a true wonder box with more capability than I'll probably ever be able to master. I recently flew Garmin's new 650/750 touch-screen systems in Florida, and they were nothing short of amazing.

Still, I can't help wondering what if…?



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