The FAA told NPR that besides confirming ADS-B signals with radar, the NextGen system will automatically check to make sure the correct receivers are picking up the correct signals. If a "ghost plane" is sending a signal to the wrong receiver, it would be spotted as fake. Third, it will use a technique called "multilateration" to determine exactly where every ADS-B signal is sent from.
Nick Foster, a partner of Brad Haines, praised the use of multilateration. "But I still wonder if it would be possible to fool the system on the edges," he told NPR. "I think the FAA should open it up and let us test it."
The risks of GPS hacks extend beyond aviation. Logan Scott, a GPS industry consultant, told Wired magazine last year [http://www.wired.com/dangerroom/2012/07/drone-hijacking/2/] that GPS is also used to control the power grid, to power banking operations including ATMs and to keep oil platforms in position. The world's cellular networks also rely on it.
And given that it is free, unauthenticated and unencrypted makes it vulnerable. "The core problem is that we've got a GPS infrastructure which is based on a security architecture out of the 1970s," Scott said.
Not everybody sees the GPS vulnerability as a major safety problem, however. Martin Fisher is now director of information security at Wellstar Health System, but worked previously in commercial aviation for 14 years. He said radar will still be around, even when the transition to NextGen is complete.
"Don't for a moment believe there won't be radar anymore," he said. "Commercial aircraft will still have anti-collision radar and proximity alarms."
Beyond that, he said, "do not make the assumption that the pilots flying your aircraft simply follow the instructions of ATC like automatons. These are very highly trained men and women with years of experience flying day, night, good weather, bad weather."
Paul Rosenzweig said he would still be much more comfortable if the FAA would allow the system to be "stress tested."
Whatever bugs are in the system, there may be more than 12 years available to fix them. The Washington Post reported in September that Calvin L. Scovel III, inspector general for the Department of Transportation, told a House subcommittee that the program was "four years behind schedule and $330 million over budget."
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