If you’ve been following the tale of LightSquared, a well-funded company which attempted to use radio frequency spectrum adjacent to that used by GPS, you may be aware how incredibly weak the satellite signals we use to navigate and shoot approaches really are. Thankfully, LightSquared, which I referenced in this space in our January issue, was recently denied approvals to build its terrestrial Wifi network in part because of its disastrous effect on GPS. But just because it appears LightSquared won’t be a continuing challenge to GPS doesn’t mean others might not appear.
In particular—and for the same signal-strength reasons LightSquared’s plans didn’t work—GPS is incredibly easy to jam. In fact, the military regularly holds exercises in which GPS jamming is conducted—check Notams and you’ll likely find mention of one. But that’s not the problem.
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Fire up your computer and Google “GPS jammer” and you’ll be rewarded with information on how easy the signals are to jam, along with links to sites where you can actually buy a device to do just that. They are used, among other things, to block certain tracking devices using GPS which are employed for perfectly reasonable purposes.
Of particular interest is a series of problems at the Newark (N.J.) Liberty International Airport (EWR) in late 2009 and the first half of 2010 involving the facility’s ground based augmentation system (GBAS), a localized version of the wide area augmentation system, WAAS. Essentially, some person or persons drove past the airport on numerous occasions while deploying a portable GPS jammer. The GBAS system at EWR was disrupted, according to an FAA PowerPoint presentation available as a PDF at tinyurl.com/avsafe-gbas.
According to a March 10, 2011, article in The Economist, FAA investigators needed two months to track down the problem: “a driver who passed by on the nearby New Jersey Turnpike each day had a cheap GPS jammer in his truck.” That article goes on to detail how some at the FAA consider the episode ”a valuable lesson” about how satellite-based systems like GPS are vulnerable.
It also should ring some alarm bells in a few cockpits, including yours. As Tom Turner’s article in this issue details beginning on page 16, an in-flight failure or widespread jamming of GPS could mean we revert back to such old-fashioned navigation methods as VOR. Tom correctly notes it’s probably been a while since we spent much time practicing to use VOR en route, much less for approaches. All of which raises many other questions, including the wisdom of putting all of the FAA’s NextGen air traffic control system eggs in GPS’s lone basket.
At present, there is no formal plan or technology to back up GPS in the U.S. This is a good time to note also that the technology itself is getting rather dated.
— Jeb Burnside
