40 Scientific American, December 2019
O
n August 5 , 2016 , CAthAy P ACifiC flight 905 from hong Kong
was heading for an on-time arrival^ at Manila’s Ninoy Aqui-
no International Airport when something unexpected
occurred. The pilots radioed air traffic controllers and said
they had lost GPS (Global Positioning System) guidance
for the final eight nautical miles to “runway right-24.”
Surprised, the controllers told the pilots to land the wide-
body Boeing 777-300 using just their own eyes. The crew mem-
bers pulled it off, but they were anxious the whole way in. Fortu-
nately, skies were mostly clear that day.
The incident was not isolated. In July and August of that year,
the International Civil Aviation Organization received more
than 50 reports of GPS interference at the Manila airport alone.
In some cases, pilots had to immediately speed up the plane and
loop around the airport to try landing again. That kind of scram-
ble can cause a crew to lose control of an aircraft. In a safety ad-
visory issued this past April, the organization wrote that avia-
tion is now dependent on uninterrupted access to satellite
positioning, navigation and timing services and that vulnerabil-
ities and threats to these systems are increasing.
In incidents involving at least four major airports in recent
years, approaching pilots have suddenly lost GPS guidance. In
June a passenger aircraft landing in Idaho nearly crashed into a
mountain, according to nA sA’s Aviation Safety Reporting Sys-
tem. Only the intervention of an alert air traffic controller avert-
ed catastrophe. Security analysts and aerospace engineers who
have studied the events say the likely cause in at least some in-
stances is malicious interference. In the best-case scenario, GPS
jamming will cause significant delays as pilots are forced to re-
route a flight’s last miles, costing airlines and passengers, says
Martin Lauth, a former air traffic controller, who now is an asso-
ciate professor of air traffic management at Florida’s Embry-
Riddle Aeronautical University.^ Crippled GPS could shut down
an airport. If someone hacked GPS and instrument landing sys-
tems at the major airports in the greater New York City area,
there would be no easy place to send arriving planes. Incoming
transoceanic flights in particular would start to run out of fuel.
Although we think of GPS as a handy tool for finding our
way to restaurants and meetups, the satellite constellation’s
timing function is now a component of every one of the 16 infra-
structure sectors deemed “critical” by the Department of Home-
land Security^ (dhs). Cell-phone networks, financial markets,
the electric grid, emergency services, and more all rely on the
timing for basic operation. Yet GPS is vulnerable. Because of the
great distance the radio waves must travel—more than 12,000
miles between satellites and receivers on Earth—the signals are
weak and easily overridden, or “jammed,” as apparently hap-
pened in Manila. They are also easy to “spoof ”: a slightly stron-
ger signal from a software-defined radio—a broadcast that can
be created by software on a laptop—can deliver a false message
or replay an authentic message infused with false information,
causing the receiver to believe it is somewhere, or some when,
it is not.
In critical infrastructure, an error of a few microseconds can
cause cascading failures that can throw off an entire network.
Todd Humphreys, an associate professor of aerospace engineer-
ing at the University of Texas at Austin, as well as Dana Goward,
a member of the U.S. National Space-Based Positioning, Naviga-
tion and Timing Advisory Board (a federal committee), and a
former executive at a major defense contractor, each told SCien-
tifiC AmeriCA n they now worry that a foreign adversary or ter-
rorist group could coordinate multiple jamming and spoofing
attacks against GPS receivers and severely degrade the function-
ality of the electric grid, cell-phone networks, stock markets,
hospitals, airports, and more—all at once, without detection.
The real shocker is that U.S. rivals do not face this vulnerabil-
ity. China, Russia and Iran have terrestrial backup systems that
GPS users can switch to and that are much more difficult to
override than the satellite-based GPS system. The U.S. has failed
to achieve a 2004 presidential directive to build such a backup.
No actual U.S. calamities have happened yet; if they had, policy
makers would have finally acted. But as disaster experts like to
note, the U.S. always seems to prepare for the previous disaster,
not the upcoming one.
Paul Tullis is a journalist in Amsterdam who writes
about the intersections of science, technology and
business. He wrote our article about how rising
numbers of tourists are ruining the Galápagos Islands.
© 2019 Scientific American
