HELSINKI/LONDON, April 30 (Reuters) - Estonia has

accused neighbouring Russia of jamming GPS navigation devices in

airspace above the Baltic states, echoing concerns from

airlines that say they have been contending with such

interference for months.

Estonian Foreign Minister Margus Tsahkna's accusation, for

which he provided no proof, followed Finnair's

decision to pause flights to Tartu in eastern Estonia for one

month due to GPS disturbances. The Kremlin did not immediately

respond to requests for comment.

There have been reports of a rise in GPS interference around

the world, particularly since last year, raising fears of an

increased risk of accidents if planes veer off-course.

WHAT IS GPS JAMMING AND SPOOFING?

GPS, short for Global Positioning System, is a network of

satellites and receiving devices used for positioning,

navigation and timing on Earth in everything from ships and

planes to cars.

GPS is one of the more important navigation tools in

aviation, which has replaced expensive ground devices that would

transmit radio beams to guide planes towards landing.

However, it is also fairly easy using store-bought tools to

block or distort GPS signals and militaries have invested in

technology that can do so.

GPS jamming uses a frequency transmitting device to block or

interfere with radio communications, usually by broadcasting

signals from the ground that are stronger than satellite-based

signals.

Spoofing might involve one country's military sending false

GPS signals to an enemy plane or drone to hinder its ability to

function and is often considered more disruptive and dangerous

than jamming.

The problem for commercial aviation comes if that false

signal is picked up by a GPS receiver in a passenger plane,

potentially confusing the pilot and air traffic control by

showing the wrong time or coordinates without warning.

WHERE DOES IT OCCUR?

In December, aviation advisory body OPSGROUP flagged a surge

in spoofing affecting private and commercial jets around the

Middle East, including Iraq, Iran and Israel, and the Black Sea.

It tends to impact areas close to war zones as the

technology is used to send suicide drones off-track.

Baltic countries have reported the issue for years,

particularly since the war in Ukraine began in 2022.

Over the past six months, jamming has worsened around the

Baltic Sea, Finnair pilot and Finnish Pilots Association Safety

and Security Committee chair Lauri Soini said.

Soini said GPS jamming now occurs in an area extending from

Poland across the Baltic states to the Swedish and Finnish

coasts, also affecting lower altitudes and maritime traffic.

While politicians and German officials have pointed to

Russia as the main culprit in the Baltic states, experts say

Western militaries, including U.S. and British forces could be

using some form of the technology in parts of the world.

WHY IS IT A PROBLEM FOR AIRLINES?

Most modern airliners have a variety of sensors and sources

to determine their positioning, in addition to GPS, meaning they

can fly if there is interference.

However, according to pilots and industry experts, airlines

still rely primarily on GPS. If jamming or spoofing occurs, GPS

might have to be switched off and cannot be reset for the

remainder of the flight in many cases.

That can cause stress and delays for take-off and landing

because certain procedures require GPS to function.

GPS navigation is also the only form of navigation for some

private jets.

However, AirBaltic safety manager and flight captain Janis

Kristops said the Tartu incident with Finnair was rare. Most

major airports have a variety of navigation tools available if

GPS isn't working, he said.

And given the diverse nature of jamming and spoofing

devices, it's difficult for the airline sector to come up with a

sweeping technological solution that can mitigate the risk.

Instead, authorities are looking to train pilots to verify

jamming and spoofing sooner.