DoT studies claim plan to adopt global positioning as sole navigation system poses risks

Affordable backups to the global positioning system (GPS) should be developed, recommends a US Department of Transportation (DoT) study. The DoT confirms GPS is vulnerable to various forms of unintentional and intentional interference.

The study, by the DoT's Volpe National Transportation Systems Center, was mandated after an inquiry into infrastructure vulnerabilities concluded plans to adopt GPS as the sole basis for navigation in US airspace by 2010 posed significant risks.

The Volpe study confirms that the low-power GPS signal "is susceptible to unintentional distruption from such causes as atmospheric effects, signal blockage from buildings and interference from communications equipment, as well as to potential deliberate disruption", says the DoT. Augmentation systems that improve GPS can still be disrupted, the study says. Systems that rely on GPS for timing synchronisation, including the Federal Aviation Administration's Nexcom digital air/ground communication system and other aviation datalinks, are also vulnerable.

In addition to a call for efforts to heighten awareness among users of GPS vulnerability, the report recommends implementing systems to monitor, report and locate sources of unintentional interference. To counter intentional disruption, the report wants military GPS anti-jamming and false signal detection technologies to be considered for civilian uses. GPS modernisation programmes, including higher-power satellites and the eventual availability of three civil frequencies will reduce vulnerability, the Volpe Center says.

The report recommends development of "affordable vehicle [aircraft]-based backups", such as GPS/inertial navigation systems (INS) and GPS/Loran-C systems, and calls for a comprehensive analysis of backup navigation and precise timing options including VOR/DME, instrument landing systems, Loran-C and INS. Meanwhile, says Volpe, modernisation of the Loran-C long-range radio-navigation network should continue.

Integrated GPS/Loran-C systems have been demonstrated, but the market for aviation-certificated Loran-C receivers evaporated after the USA announced plans to deactivate the ground station network. The Volpe Center recommends that, if Loran-C is determined to have a navigation role, "DoT should promptly announce this to encourage the electronics manufacturing community to develop new Loran-C technologies".

Source: Flight International