FAA Files Reveal a
Surprising Threat to Airline Safety: the U.S. Military's GPS Tests
Military tests that
jam and spoof GPS signals are an accident waiting to happen
Early one morning
last May, a commercial airliner was approaching El Paso International
Airport, in West Texas, when a warning popped up in the cockpit: “GPS
Position Lost.” The pilot contacted the airline’s operations center and
received a report that the U.S. Army’s White Sands Missile Range, in South
Central New Mexico, was disrupting the GPS signal. “We knew then that it
was not an aircraft GPS fault,” the pilot wrote later.
The pilot missed an
approach on one runway due to high winds, then came around to try again.
“We were forced to Runway 04 with a predawn landing with no access to [an
instrument landing] with vertical guidance,” the pilot wrote. “Runway
04…has a high CFIT threat due to the climbing terrain in the local area.”
CFIT stands for
“controlled flight into terrain,” and it is exactly as serious as it
sounds. The pilot considered diverting to Albuquerque, 370 kilometers away,
but eventually bit the bullet and tackled Runway 04 using only visual aids.
The plane made it safely to the ground, but the pilot later logged the
experience on NASA’s Aviation Safety Reporting System, a forum where pilots
can anonymously share near misses and safety tips.
This is far from the
most worrying ASRS report involving GPS jamming. In August 2018, a
passenger aircraft in Idaho, flying in smoky conditions, reportedly
suffered GPS interference from military tests and was saved from crashing into
a mountain only by the last-minute intervention of an air traffic
controller. “Loss of life can happen because air traffic control and a
flight crew believe their equipment are working as intended, but are in
fact leading them into the side of the mountain,” wrote the controller.
“Had [we] not noticed, that flight crew and the passengers would be dead. I
have no doubt.”
There are some 90
ASRS reports detailing GPS interference in the United States over the past
eight years, the majority of which were filed in 2019 and 2020. Now IEEE
Spectrum has new evidence that GPS disruption to commercial aviation is
much more common than even the ASRS database suggests. Previously
undisclosed Federal Aviation Administration (FAA) data for a few months in
2017 and 2018 detail hundreds of aircraft losing GPS reception in the
vicinity of military tests. On a single day in March 2018, 21 aircraft
reported GPS problems to air traffic controllers near Los Angeles. These
included a medevac helicopter, several private planes, and a dozen
commercial passenger jets. Some managed to keep flying normally; others
required help from air traffic controllers. Five aircraft reported making
unexpected turns or navigating off course. In all likelihood, there are
many hundreds, possibly thousands, of such incidents each year nationwide,
each one a potential accident. The vast majority of this disruption can be
traced back to the U.S. military, which now routinely jams GPS signals over
wide areas on an almost daily basis somewhere in the country.
How to access
reports on NASA’s Aviation Safety Reporting System
1: To investigate a
report, go to the ASRS database: https://asrs.arc.nasa.gov/
2: On the top
ribbon, click “Search ASRS Database,” and then choose “Search ASRS Online.”
Click on “Start Search.”
3: Follow the steps
under “How to Search” at the top. Then, under 7 “Text: Narrative/Synopsis,”
click on “[words].” Then click on “Text contains Click Here.”
4: In the pop-up
window, enter some of the text that is quoted in this story. In the “Fields
to search” field at the bottom, click “Narrative” (but you can also try
“Synopsis”).
5: If you’re
searching on more than one word, you need to format it inside parentheses,
thus: (GPS JAMMING).
6: Click “Save.” The
pop-up will disappear.
7: Click “Run
Search” at the bottom right.
8: Under “Display
your results,” click “View all reports.”
The military is
jamming GPS signals to develop its own defenses against GPS jamming.
Ironically, though, the Pentagon’s efforts to safeguard its own troops and
systems are putting the lives of civilian pilots, passengers, and crew at
risk. In 2013, the military essentially admitted as much in a report,
saying that “planned EA [electronic attack] testing occasionally causes
interference to GPS based flight operations, and impacts the efficiency and
economy of some aviation operations.”
In the early days of
aviation, pilots would navigate using road maps in daylight and follow
bonfires or searchlights after dark. By World War II, radio beacons had
become common. From the late 1940s, ground stations began broadcasting
omnidirectional VHF signals that planes could lock on to, while
shorter-range systems indicated safe glide slopes to help pilots land. At
their peak, in 2000, there were more than a thousand very high frequency
(VHF) navigation stations in the United States. However, in areas with
widely spaced stations, pilots were forced to take zigzag routes from one
station to the next, and reception of the VHF signals could be hampered by
nearby buildings and hills.
Everything changed
with the advent of global navigation satellite systems (GNSS), first
devised by the U.S. military in the 1960s. The arrival in the mid-1990s of
the civilian version of the technology, called the Global Positioning
System, meant that aircraft could navigate by satellite and take direct
routes from point to point; GPS location and altitude data was also
accurate enough to help them land.
The FAA is about
halfway through its NextGen effort, which is intended to make flying safer
and more efficient through a wholesale switch from ground-based navigation
aids like radio beacons to a primarily satellite-enabled navigation system.
Along with that switch, the agency began decommissioning VHF navigation
stations a decade ago. The United States is now well on its way to having a
minimal backup network of fewer than 600 ground stations.
Meanwhile, the
reliance on GPS is changing the practice of flying and the habits of
pilots. As GPS receivers have become cheaper, smaller, and more capable,
they have become more common and more widely integrated. Most airplanes
must now carry Automatic Dependent Surveillance-Broadcast (ADS-B)
transponders, which use GPS to calculate and broadcast their altitude,
heading, and speed. Private pilots use digital charts on tablet computers,
while GPS data underpins autopilot and flight-management computers. Pilots
should theoretically still be able to navigate, fly, and land without any
GPS assistance at all, using legacy radio systems and visual aids.
Commercial airlines, in particular, have a range of backup technologies at
their disposal. But because GPS is so widespread and reliable, pilots are
in danger of forgetting these manual techniques.
When an Airbus
passenger jet suddenly lost GPS near Salt Lake City in June 2019, its pilot
suffered “a fair amount of confusion,” according to the pilot’s ASRS
report. “To say that my raw data navigation skills were lacking is an
understatement! I’ve never done it on the Airbus and can’t remember having
done it in 25 years or more.”
“I don’t blame
pilots for getting a little addicted to GPS,” says Todd E. Humphreys, director
of the Radionavigation Laboratory at the University of Texas at Austin.
“When something works well 99.99 percent of the time, humans don’t do well
in being vigilant for that 0.01 percent of the time that it doesn’t.”
Losing GPS
completely is not the worst that can happen. It is far more dangerous when
accurate GPS data is quietly replaced by misleading information. The ASRS
database contains many accounts of pilots belatedly realizing that
GPS-enabled autopilots had taken them many kilometers in the wrong
direction, into forbidden military areas, or dangerously close to other
aircraft.
In December 2012, an
air traffic controller noticed that a westbound passenger jet near Reno,
Nev., had veered 16 kilometers (10 miles) off course. The controller confirmed
that military GPS jamming was to blame and gave new directions, but later
noted: “If the pilot would have noticed they were off course before I did
and corrected the course, it would have caused [the] aircraft to turn right
into [an] opposite direction, eastbound [jet].”
So why is the
military interfering so regularly with such a safety-critical system?
Although most GPS receivers today are found in consumer smartphones, GPS
was designed by the U.S. military, for the U.S. military. The Pentagon depends
heavily on GPS to locate and navigate its aircraft, ships, tanks, and
troops.
The U.S. military
routinely jams GPS signals over wide areas on an almost daily basis
For such a vital
resource, GPS is exceedingly vulnerable to attack. By the time GPS signals
reach the ground, they are so faint they can be easily drowned out by
interference, whether accidental or malicious. Building a basic electronic
warfare setup to disrupt these weak signals is trivially easy, says
Humphreys: “Detune the oscillator in a microwave oven and you’ve got a
superpowerful jammer that works over many kilometers.” Illegal GPS jamming
devices are widely available on the black market, some of them marketed to
professional drivers who may want to avoid being tracked while working.
Other GNSS systems,
such as Russia’s GLONASS, China’s BeiDou, and Europe's Galileo
constellations, use slightly different frequencies but have similar
vulnerabilities, depending on exactly who is conducting the test or attack.
In China, mysterious attacks have successfully “spoofed” ships with GPS
receivers toward fake locations, while vessels relying on BeiDou reportedly
remain unaffected. Similarly, GPS signals are regularly jammed in the
eastern Mediterranean, Norway, and Finland, while the Galileo system is
untargeted in the same attacks.
The Pentagon uses
its more remote military bases, many in the American West, to test how its
forces operate under GPS denial, and presumably to develop its own
electronic warfare systems and countermeasures. The United States has
carried out experiments in spoofing GPS signals on at least one occasion,
during which it was reported to have taken great care not to affect
civilian aircraft.
Despite this, many
ASRS reports record GPS units delivering incorrect positions rather than
failing altogether, but this can also happen when the satellite signals are
degraded. Whatever the nature of its tests, the military’s GPS jamming can
end up disrupting service for civilian users, particularly high-altitude
commercial aircraft, even at a considerable distance.
The military issues
Notices to Airmen (NOTAM) to warn pilots of upcoming tests. Many of these
notices cover hundreds of thousands of square kilometers. There have been
notices that warn of GPS disruption over all of Texas or even the entire
American Southwest. Such a notice doesn’t mean that GPS service will be
disrupted throughout the area, only that it might be disrupted. And that
uncertainty creates its own problems.
In 2017, the FAA
commissioned the nonprofit Radio Technical Commission for Aeronautics to
look into the effects of intentional GPS interference on civilian aircraft.
Its report, issued the following year by the RTCA’s GPS Interference Task
Group, found that the number of military GPS tests had almost tripled from
2012 to 2017. Unsurprisingly, ASRS safety reports referencing GPS jamming
are also on the rise. There were 38 such ASRS narratives in 2019—nearly a
tenfold increase over 2018
Chart describing GPS
Problems.
New internal FAA
materials obtained by Spectrum from a member of the task group and not
previously made public indicate that the ASRS accounts represent only the
tip of the iceberg. The FAA data consists of pilots’ reports of GPS
interference to the Los Angeles Air Route Traffic Control Center, one of 22
air traffic control centers in the United States. Controllers there oversee
air traffic across central and Southern California, southern Nevada,
southwestern Utah, western Arizona, and portions of the Pacific Ocean—areas
heavily affected by military GPS testing.
This data includes
173 instances of lost or intermittent GPS during a six-month period of 2017
and another 60 over two months in early 2018. These reports are less
detailed than those in the ASRS database, but they show aircraft flying off
course, accidentally entering military airspace, being unable to maneuver,
and losing their ability to navigate when close to other aircraft. Many
pilots required the assistance of air traffic control to continue their
flights. The affected aircraft included a pet rescue shuttle, a hot-air
balloon, multiple medical flights, and many private planes and passenger
jets.
In at least a
handful of episodes, the loss of GPS was deemed an emergency. Pilots of
five aircraft, including a Southwest Airlines flight from Las Vegas to
Chicago, invoked the
“stop buzzer,” a request routed through air traffic control for the
military to immediately cease jamming. According to the Aircraft Owners and
Pilots Association, pilots must use this phrase only when a
safety-of-flight issue is encountered.
To be sure, many
other instances in the FAA data were benign. In early March 2017, for
example, Jim Yoder was flying a Cessna jet owned by entrepreneur and space
tourist Dennis Tito between Las Vegas and Palm Springs, Calif., when both
onboard GPS devices were jammed. “This is the only time I’ve ever had GPS
go out, and it was interesting because I hadn’t thought about it really
much,” Yoder told Spectrum. “I asked air traffic control what was going on
and they were like, ‘I don’t really know.’ But we didn’t lose our ability
to navigate, and I don’t think we ever got off course.”
Indeed, one of the
RTCA task group’s conclusions was that the Notice to Airmen system was part
of the problem: Most pilots who fly through affected areas experience no
ill effects, causing some to simply ignore such warnings in the future.
“We call the NOTAMs
‘Chicken Little,’ ” says Rune Duke, who was cochair of the RTCA’s task
group. “They say the sky is falling over large areas…and it’s not
realistic. There are mountains and all kinds of things that would prevent
GPS interference from making it 500 nautical miles [926 km] from where it
is initiated.”
GPS interference can
be affected by the terrain, aircraft altitude and attitude, direction of
flight, angle to and distance from the center of the interference,
equipment aboard the plane, and many other factors, concluded the task
group, which included representatives of the FAA, airlines, pilots,
aircraft manufacturers, and the U.S. military. One aircraft could lose all
GPS reception, even as another one nearby is completely unaffected. One
military test might pass unnoticed while another causes chaos in the skies.
This unreliability
has consequences. In 2014, a passenger plane approaching El Paso had to
abort its landing after losing GPS reception. “This is the first time in my
flying career that I have experienced or even heard of GPS signal jamming,”
wrote the pilot in an ASRS report. “Although it was in the NOTAMs, it still
caught us by surprise as we really did not expect to lose all GPS signals at
any point. It was a good thing the weather was good or this could have
become a real issue.”
Sometimes air
traffic controllers are as much in the dark as pilots. “They are the last
line of defense,” the FAA’s Duke told Spectrum. “And in many cases, air traffic
control was not even aware of the GPS interference taking place.”
The RTCA report made
many recommendations. The Department of Defense could improve coordination
with the FAA, and it could refrain from testing GPS during periods of high
air traffic. The FAA could overhaul its data collection and analysis, match
anecdotal reports with digital data, and improve documentation of adverse
events. The NOTAM system could be made easier to interpret, with warnings
that more accurately match the experiences of pilots and controllers.
One aircraft could
lose all GPS reception, even as another one nearby is completely
unaffected.
Remarkably, until
the report came out, the FAA had been instructing pilots to report GPS
anomalies only when they needed assistance from air traffic control. “The
data has been somewhat of a challenge because we’ve somewhat discouraged
reporting,” says Duke. “This has led the FAA to believe it’s not been such
a problem.”
NOTAMs now encourage
pilots to report all GPS interference, but many of the RTCA’s other
recommendations are languishing within the Office of Accident Investigation
and Prevention at the FAA.
New developments are
making the problem worse. The NextGen project is accelerating the move of
commercial aviation to satellite-enabled navigation. Emerging autonomous
air systems, such as drones and air taxis, will put even more weight on
GPS’s shaky shoulders.
When any new
aircraft is adopted, it risks posing new challenges to the system. The
Embraer EMB-505 Phenom 300, for instance, entered service in 2009 and has
since become the world’s best-selling light jet. In 2016, the FAA warned
that if the Phenom 300 encountered an unreliable or unavailable GPS signal,
it could enter a Dutch roll (named for a Dutch skating technique), a
dangerous combination of wagging and rocking that could cause pilots to
lose control. The FAA instructed Phenom 300 owners to avoid all areas of
GPS interference.
As GPS assumes an
ever more prominent role, the military is naturally taking a stronger
interest in it. “Year over year, the military’s need for GPS
interference-event testing has increased,” says Duke. “There was an
increase again in 2019, partly because of counter-UAS [drone] activity. And
they’re now doing GPS interference where they previously had not, like
Michigan, Wisconsin, and the Dakotas, because it adds to the realism of any
type of military training.”
So there are ever
more GPS-jamming tests, more aircraft navigating by satellite, and more
pilots utterly reliant on GPS. It is a feedback loop, and it constantly
raises the chances that one of these near misses and stop buzzers will end
in catastrophe.
When asked to
comment, the FAA said it has established a resilient navigation and
surveillance infrastructure to enable aircraft to continue safe operations
during a GPS outage, including radio beacons and radars. It also noted that
it and other agencies are working to create a long-term GPS backup solution
that will provide position, navigation, and timing—again, to minimize the
effects of a loss of GPS.
However, in a report
to Congress in April 2020, the agency coordinating this effort, the U.S.
Department of Homeland Security, wrote: “DHS recommends that responsibility
for mitigating temporary GPS outages be the responsibility of the
individual user and not the responsibility of the Federal Government.” In
short, the problem of GPS interference is not going away.
In September 2019,
the pilot of a small business jet reported experienced jamming on a flight
into New Mexico. He could hear that aircraft all around him were also
affected, with some being forced to descend for safety. “Since the FAA is
deprecating [ground-based radio aids], we are becoming dependent upon an
unreliable navigation system,” wrote the pilot upon landing. “This
extremely frequent [interference with] critical GPS navigation is a
significant threat to aviation safety. This jamming has to end.”
The same pilot was
jammed again on his way home.
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