Several years ago, when satellites were being touted as aviation’s sole means of navigation from takeoff to touchdown, former FAA Administrator Langhorne Bond painted a picture of a dark winter’s night with below-limits weather up and down the east coast. In that scenario, he stated, terrorist GPS jammers could become “weapons of mass destruction.” The FAA shrugged it off as unfounded speculation. But in a recent report on the GPS-dependent ADS-B, the DOT’s Inspector General took the matter much more seriously, calling on the FAA to “work with the U.S. intelligence community to assess such potential threats.”

Surprisingly, therefore, it now turns out that today, the most likely carriers of these weapons of mass destruction are the good ol’ boys and gals driving the country’s 18-wheeler fleet. How come? Blame it on the ubiquity of GPS, and its ever expanding applications. Almost all big trucks now carry small GPS receivers atop their cabs, along with companion cellphones, that allow company dispatchers to monitor progress without talking with the driver.

And, yes, you guessed it. When a driver wants to make an unauthorized stop for a coffee or whatever, he or she plugs a small GPS jammer into the cigarette lighter, overwhelming the weak satellite signals with interference hash. To counter this, the tracking system developers then found they could roughly triangulate the cellphone’s location from three cell towers. In response, newer GPS jammers can now also jam incoming cellphone interrogations, defeating triangulation attempts. The cat-and-mouse game continues.

And these jammers are cheap. In a New Year’s sale on the Internet, a Chinese GPS/cellphone unit was offered for $22.65. However, the range of its interference signals was just over five yards, which would probably put off most potential buyers, even though it would be adequate to disable the GPS and associated cellphone receivers on a truck cab roof just above the driver’s head. But most customers probably want more power, opting for more muscular units with advertised ranges of three miles or more. A macho thing, maybe, but that’s where the trouble starts, as it has at Newark’s Liberty International Airport.

Laas Interference

During testing last year of Newark’s newly installed GPS Laas precision approach aid on Runway 29, the system frequently, and inexplicably, shut itself down. The cause was eventually found to be interference from high-powered GPS jammers on trucks passing on the nearby New Jersey Turnpike.

This has placed the owners of the Laas equipment–the Port Authority of New York and New Jersey (PANYNJ)–as well as Continental Airlines and the FAA, in something of a quandary. In a December 2008 PANYNJ news release, the Authority estimated that it would spend $2.5 million for the purchase, installation and maintenance of the ground system; Continental would spend approximately $1.1 million in equipping 15 aircraft and training pilots, and the FAA would commit to $2.5 million in technology assessment. More recently, the FAA has reported that by August 2010, Continental had equipped 18 Boeing 737NGs.

Until the jamming threat is ameliorated, Newark’s Laas installation cannot be certified for IFR approaches. AIN understands that Honeywell–the system’s manufacturer–aims to have an interference-mitigation project (but not necessarily a final solution) ready for FAA testing and certification by the summer, in readiness for incorporation in the Laas planned for Continental’s other major base at Houston, and for retrofit to the Newark system.

The legal issues pertaining to GPS jamming are not entirely clear. It is certainly illegal to deliberately interfere with state or federal facilities, or with public transportation and safety, the deliberate use of lasers against aircraft an obvious example. But while nabbing someone pointing a laser at an aircraft following pilot reports is one thing, proving in a court that interference to a nearby ATC system from a specific passing vehicle was deliberate, rather than inadvertent, would be quite another. Reportedly, there are several thousand GPS/cellphone jammers in current use, many in vehicles other than trucks.

Indeed, one group that doubtless will follow Honeywell’s investigation closely is the law-enforcement community. The miniature GPS and cellphone receivers atop truck cab roofs–when packaged with a small but powerful magnet–can be surreptitiously slipped inside a wheel well of a suspect’s car by an agent as he bends to apparently tie a loose shoe lace, thereby allowing the car to be accurately tracked back at headquarters. Suspicious spouses are also said to have concealed such units in their partners’ vehicles.

Conversely, however, sophisticated criminals and errant partners are equally likely to invest in a jammer’s ability to shake off such unwelcome attention. Consequently, the future ping-pong battle of GPS jamming measures versus countermeasures can be expected to be fought not only on the nation’s airports, but on its highways as well.