Avionics News July 2023 - 30

TAKING GPS FOR GRANTED
Continued from page 29
University's fleet of training aircraft and does installs on a variety
of business jets. He deals with GPS issues, which at times
include interference. " We have seen portable cellular devices
affected by GPS, " he said. " It has not been prevalent in the past
10 years, but it used to happen a lot. I guess with the changing
cellular technology, it has not been as much of an issue as the
systems evolve from 4G to 5G. That has always been a concern
that the next cellular device might cause a problem because
they all have transmitters in them that could potentially cause
GPS to fall offline. So whenever a customer says, 'I am losing
GPS intermittently,' the first thing we say is, 'Did you turn off
your cellular devices?' "
It also sometimes happens that communications radios on
the aircraft can knock out GPS, and this also used to be more
of a problem than it is now. Moorefield thinks GPS manufacturers
have installed better shielding/filtering to keep this
problem to a minimum.
In one case, he learned that skin current buildup on a plane
caused GPS to drop off in flight. This was on a fast, slick airplane
that had several damaged static wicks.
The RNT Foundation advocates for the multiple diverse
methods of PNT delivery approach advocated by the U.S.
Department of Transportation. After a Department of Transportation
GPS backup technology demonstration project at
the Volpe Center in 2021, the conclusion was the U.S. needs a
coordinated approach that involves signals from space and terrestrial
transmissions with the transmitters linked by fiber. Just
what form a backup system would take is part of the debate,
whether it be a revival of the U.S. Coast Guard Loran navigation
system as an eLoran or something else. Goward acknowledged
eLoran would not be as precise as GPS, but it would
be a powerful terrestrial system that would complement GPS
well. Parkinson noted eLoran would only be two dimensional,
local and have accuracies of tens of meters when farmers, for
example, require centimeters.
There have been increasing incidents of GPS interference in
Europe and a few notable ones in the United States.
A technical paper published in 2022 by researchers led by
Michael Felux of Zurich University last year, titled " Analysis
of GNSS disruptions in European Airspace, " reviewed radio
frequency interference hotspots that were disrupting GNSS.
The period covered was from February to August 2022. Analysis
was performed on crowdsourced ADS-B data from the
OpenSky Network with interference found in the Baltic states,
Poland, Eastern Europe and the Eastern Mediterranean. Some
of these areas are affected by conflict in Ukraine and Syria.
Some events were isolated, others affected thousands of
flights per day. While only 1.6% of flights were affected in the
30 avionics news * july 2023
Baltic states and Kaliningrad, 14% were affected in Romania
and Bulgaria and more than 70% in the Cyprus area. Some
flights relying solely on GNSS might have needed radar
assistance from air traffic control. The authors wrote that while
most aircraft do not rely exclusively on GNSS for air navigation,
the interference causes nuisance warnings on the flight
deck and increases pilot workload.
Recent incidents in the United States include one reported in
NASA's Aviation Reporting System. In June 2019, an alert Salt
Lake City air traffic controller noticed a flight navigation error,
" purportedly the result of GPS jamming, " and quick action was
needed to avert a disaster.
Pilots were reporting widespread GPS jamming and outages
in the area with two aircraft reporting problems prior to the
initial approach fix on an approach. Then, one passenger aircraft
reported it was at an intersection at 11,000 feet on approach to
Friedman Memorial Airport at Sun Valley, Idaho. When spotted
by a Salt Lake City radar controller, the aircraft was not where
the pilot said it was. Rather than at the intersection, it was 12
nautical miles away and only 3 miles from a 10,700-foot minimum
IFR altitude in mountainous terrain. The radar controller
issued a turn, and a CFIT collision with a mountain was avoided.
Goward added that as a result of the Sun Valley incident and
input from numerous aviation groups, the International Civil
Aviation Organization has informed its members of an " urgent
need to address harmful interference " with satnav signals.
In another case, interference can be spotted on a new website
named GPSJam.org created last year by aviation analyst
John Wiseman. On a map of the world, it shows areas in
yellow with 2% to 10% of ADS-B reports showing low navigation
availability. Red areas have more than 10% levels of
interference, hence unacceptable availability. Parkinson added
that the main negative effect of interference on a well-designed
GNSS system is not degraded accuracy but rather availability.
While poorly designed systems can be spoofed, the usual effect
of interference is to deny use.
Civil aviation can be affected by jamming that isn't even intended
to disrupt its operations. Potential sources include GPS
jammers fitted to road vehicles and even solar activity. In addition,
nation states and other groups that may want to disrupt
civil aviation can directly target aviation activities and disrupt
civil air navigation. Goward noted that illegal GPS jamming
devices are inexpensive, and some truck drivers, for example,
use them to keep out of sight of their company's fleet tracking
system. However, most GPS interference is unintentional.
A two-year European Union study found out of hundreds of
thousands of potentially harmful signals, only about 10% were
intentional.
Goward added, " In two separate incidents last year, strong
interference near Denver and Dallas airports impacted air
traffic, each for more than a day. The Denver incident lasted for
http://www.GPSJam.org
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