FAA drops GPS bombshell

At the recent ICAO CNS/ATM implementation conference in Rio de Janeiro, the FAA dropped a bombshell by announcing, contrary to all earlier assurances, that the Global Positioning System (GPS) would not be approved for sole use navigation, and would need a backup. The reason given was that the possibilities of jamming, solar events, etc., were now better understood.
Excellent though GPS may be, its problem is that it is so low powered that the signal can easily be blouted out or disrupted - as demonstrated at last year's Moscow air show where a jammer destroyed the signal over a radius of 200 km, and numerous DoD excercises. The notion of GPS as sole means of navigation is dead, even with WAAS and LAAS augmentation systems. Suitable backup systems cited are triple inertial, VOR/DME and LORAN C.
The implications of the FAA's new position are many - ranging from the need to maintain a ground based ILS and VOR/DME/NDB navigation aids system way beyond the timescale the world had been led to expect, to the probable continued operation of LORAN-C chains. Earlier the DoT had planned to shut down Loran at end-2000. As of September 1998, the DoT confirmed that the existing LORAN-C chains will be maintained and upgraded, at least to 2008, "in the transition period to satellite-based navigation".
LORAN-C is a long range, low frequency (100 kHz), hyperbolic navigation system developed by the USA in the 1960s primarily for maritime defence purposes. Loran is very difficult to jam, and the coverage includes the whole of the USA and seaboard, down to ground/sea level, plus other regional chains. Navigational accuracy is determined by means of measured differences in times-of-arrival between signals from synchronised transmitters at surveyed locations. Loran-C is greatly appreciated by the US general aviation community (with some 80,000 aircraft equipped), though it never caught on in Europe for aviation purposes due to gaps in coverage. A majority of the 1.3 million Loran sets in use worldwide are for mariners. Loran is also cheap - a figure of $12 million a year has been quoted to operate and modernise the existing 26 US Loran stations.
Under the 1994 Federal Radionavigation Plan, with GPS promised as better performing replacement, the DoT advanced to the phase-out date of Loran from 2015 to 2000, dealing a body blow to the system operated by the US Coast Guard. Outside the US, the Coast Guard left individual countries to decide whether to continue their own operations.
In north-west Europe, where Loran was used primarily as an air to land and maritime navigation, and where the GPS/DoT lobby was not so strong, Denmark, France, Germany, Ireland, Norway and the Netherlands teamed up in NELS (Northwest European Loran-C System) to modernise existing transmitters and estabilish some new ones. NELS, up and running since April 1998, with the exception of the delayed Irish station, may be enlarged to include two Italian stations to extend coverage in the Mediterranean, and include a linkup with the Russian Chayka system, which can also be received by the modern Loran receivers, in the western Arctic, the Baltic (Belarus) and the Crimea.
It appears on the cards that the DoT will extend and modernise the Loran-C system as an economical backup to GPS, at least until 2008, or until the arrival of a failsafe GNSS-2, under international control.
Oliver Sutton - INTERAVIA September 1998

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