"It starts when you get to 5,000ft above the ground," says pilot Akseli.
As the airplane climbs higher, the status display tells pilots that the GPS signal is lost, he says, but if spoofing is occurring then there can be false reports too:
"You might get false ground proximity warnings like 'Terrain ahead, terrain ahead, pull up, pull up'."
Akseli flies passenger liners - generally Airbus A320s and A330s - for Finnair out of Helsinki Airport.
"In general it’s not dangerous… but when you are acting - intentionally or unintentionally - against a commercial flight it builds up some risks."
Helsinki Airport. Pic: Finavia Oyj
Helsinki Airport. Pic: Finavia Oyj
Spoofing is more dangerous than jamming, says Sean Fitzpatrick, an experienced pilot, because the plane is receiving false information. "And that can corrupt certain systems."
"When it first started you had aircraft warning systems going off at 33,000ft... saying you're going to fly on the side of a hill and they're like, what the hell's going on here?"
Nowadays there are protocols in place to deal with it, he says, and pilots can turn off navigation systems to minimise disruption. Sean says flying remains safe.
What happens when a cockpit dashboard lies to the pilot? Pic: AP
What happens when a cockpit dashboard lies to the pilot? Pic: AP
Recently he experienced GPS interference while flying a Boeing 747 in Saudi Arabian airspace, just south of the border with Jordan.
"All of a sudden, the GPS got corrupted signals because of spoofing and it thought I was 200 miles to the north - in Syria," Sean says. "So then [the autopilot] started correcting to the left. The plane started turning and it's like, what are you doing?"
According to Sean, there are some places where the airways are "pretty tight": "If you're not on top of it the aircraft starts turning towards areas you don't want to be going in."
A report released in September 2024 by OPS Group - an organisation of pilots, flight dispatchers, schedulers and controllers - found that the impact of spoofing on flight safety, aircraft operation and handling, and air traffic control operations is "extremely significant".
The group claimed that with "few exceptions", spoofing is being used by "state actors" as a result of regional conflict.
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Some in the aviation industry are increasingly worried about spoofing
Some in the aviation industry are increasingly worried about spoofing
"To date, no aircraft has been directly targeted. However... were this to change, the impacts could be even more severe."OPS Group report
It pointed to the Ground Proximity Warning System, which is designed to detect if a plane is too close to the ground, as the "greatest safety concern". "The number of false alerts is astounding. There is an increasing normalisation of risk," the report said.