Jamming of the essential navigational satellite signal has caused enough headaches for the EU air traffic control organisation to prompt an investigation, complete with an instrumented aircraft designed to detect signs of GPS jamming.
Airliners rely on GPS to a great extent, and air traffic management (the science of making sure airliners don’t come dangerously close to each other) is almost solely focused nowadays on building approach paths and airways that are defined by GPS waypoints.
Eurocontrol “started collecting GNSS outage reports by pilots in 2014, following up significant numbers of outage reports in a given area to determine cause and impact, and to support the [air traffic control company] and operators in question,” said the organisation in its report [PDF], adding that between 2017 and 2018, reported outages increased by 2,000 percentage points, rising from 154 in 2017 to a whopping 4,364 the following year.
Most of this jamming is focused on the Eastern Mediterranean and specifically affects Cyprus, Eurocontrol said. During a three-hour period in February 2020, a fifth of all flights passing through Cypriot airspace were affected, said the air traffic control org, extrapolating from a research flight it operated with an instrumented Airbus A320 that flew south of Cyprus itself.
The eastern Med, especially around Syria and Lebanon, has long been a conflict zone – and air forces from West and East alike have long been jamming GPS as part of their military operations there.
“Larnaca could become an absolute shitshow when the Americans jammed it,” an airline pilot told The Register. Describing one incident, where a radar* contact that was “going at least 50 per cent faster than us” passed below his aircraft, the pilot said it seemed to be on course for Sicily shortly before his own aircraft had a GPS failure.
“Luckily at that point, because at high altitude, it’s irritating, but not a major issue. Because for short term, you’ve got your eyes and your internal navigation system,” said the pilot.
It has deeper effects, however. “The main issue is when it happens in Larnaca (eastern Cyprus), because you’re right next to mountains and [you’re following a] GNSS approach. And if you get jammed, it causes the map to shift and the plane then decides that it’s currently inside a mountain. Sets off all of your terrain warnings.”
Triggering a terrain warning means immediately having to perform a prescribed escape manoeuvre that can mean breaking off an otherwise safe approach to land, said the pilot, who spoke on condition of anonymity because he is not an official spokesman for his airline. This causes delays and potentially extra costs to the airline and its passengers.
As for Eurocontrol, the body plaintively concluded: “At national level, local RFI [radio frequency interference] mitigation measures need to be taken, ideally including the ability to conduct in-flight RFI measurements.
“While the majority of RFI hotspots appear to originate in conflict zones, they affect commercial aviation at large distances from these zones, reflecting a disproportionate use of jamming that appears to go well beyond simple military mission effectiveness.”
So far the problem’s been formally identified: but, other than flying around jamming zones, what else can pilots do?