John Sheridan

Resilience–broadly, the ability to readily recover from external disturbances–seems likely to become the next buzzword in aviation’s lexicon. It is gaining acceptance primarily to describe a future world air navigation system’s resistance to interruptions and outright signal loss, to provide pilots with essential, unfailing position, navigation and timing (PNT) data. Resilience came to the fore at a February conference on GNSS vulnerability, sponsored by the UK Institute of Navigation. 
“PNT service has become a worldwide utility–thanks to GPS,” pointed out keynote speaker Dr. Brad Parkinson, known as “the father of GPS” for his earlier leadership as a USAF Colonel in the system’s development. In fact, he added, “PNT service is now worth billions of dollars a year, yet taken for granted. On the other hand, this service is potentially threatened by jamming and related threats. I subscribe to PTA–protect, toughen and augment–this valuable asset. Particularly appealing is the use of eLoran to augment or serve as a stand-alone service. In this role, eLoran would be a powerful deterrent to malicious interference.”
Most AIN readers will be aware of the potential threats of GPS jamming, where commissioning of a prototype Laas/GBAS installation at Newark was delayed several months <a href="http://www.ainonline.com/aviation-news/aviation-international-news/2011-01-27/gpscellphone-jammers-also-snarl-aviation-navigation-systems">by intermittent, yet inexplicable, interference, found eventually to emanate from a small, $35 GPS jammer</a> in a passing vehicle on a nearby highway. Parkinson’s “related threats” include that of a large private yacht in the Mediterranean, where invited engineers from the University of Texas caused it to slowly alter course by following their false “spoofed” GPS transmissions, which remained invisible to the yacht’s crew. 
The Case for eLoran
So why does Parkinson endorse eLoran? Basically, for its modernized performance, essentially mirroring GPS, with highly accurate, long-range and unjammable surface to stratosphere coverage, coupled with GPS-like “all in view” signals. What’s more–and this is critical–eLoran can use the existing ground stations and large antennas used by its loran-C predecessor to cover the continental U.S., thereby re-using the U.S. government’s earlier multimillion-dollar loran-C investment. Even better, several overseas nations, such as Russia, Korea, Japan, China and Saudi Arabia, still operate loran-C networks, with eLoran upgrades reportedly planned. The UK, France and the Netherlands are already using eLoran in marine operations, with recent tests in the Netherlands demonstrating 5-meter differential position accuracies in coastal and harbor applications.
At the same time, the world’s GNSS constellation operators are looking to more advanced capabilities across their networks where, using technology developments planned for 2025, future-generation GNSS receivers will automatically select individual satellites from separate constellations to derive the best possible fix “geometry” to ensure optimum PNT, GBAS and SBAS performance over almost the whole globe. When combined with eLoran, this would effectively end the threat of interference and jamming, by providing a level of resilience that we have never experienced before.

Future of Air Navigation: Resilience to Vulnerability

Position, navigation and timing data has become a worldwide utility&#8211;thanks to GPS.

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