"It's all about procedures. How operators fly, how they behave. There's nothing behind the system," said Värk.

On Monday afternoon, despite GPS interference, several small planes arriving there were helped to land at Tartu Airport by air traffic controllers in Tallinn.

Kristi Seppa, head of the aviation services department at the Estonian Aviation Academy, said that conventional systems such as NDBs (non-directional beacons) and VOR (very high frequency (VHF) omni-directional ranges) are no longer in use in Estonia, with all flying now utilizing GPS approaches.

According to Seppa, in the event of a GGPS signal loss, Finnair pilots have little room to maneuver when landing in Tartu.

"There is nothing the pilot can do. They have manuals and procedures. What instruments they have are in working order and they act according to company procedures. Some write in their procedures that you can do night circling. [It's] the kind of thing where you fly to the airport. If the conditions are good, you can land with a visual. Or it may be written in the procedures that a visual approach is allowed. However, that requires the pilot to physically see the runway, she said.

As long as the GPS at Tartu Airport cannot be relied on, Seppa believes the only solution would be to restore air traffic control services in Tartu itself, rather than rely on flight information provided from Tallinn. This, however, would require staff to be re-trained.

"This would be the most sensible option. This is purely an air traffic management issue. But even if someone decided to do it overnight, it would not be possible. Air traffic controllers would first need to re-qualify. This could take three to six months. There are no good immediate solutions," said Seppa.

Over the weekend, Estonia's Agency for Consumer Protection and Technical Supervision (TTJA) sent its measurement teams to Tartu to investigate the GPS jamming. As expected, no GPS interference was detected there on the ground.

The GPS jamming begins at an altitude of around one and a half kilometers in the airspace and, according to Erko Kulu, head of the TTJA's frequency management service is not aimed at attacking Estonia.

"Our assessment is that they (Russia - ed.) are trying to use this to carry out drone strikes [in Ukraine – ed.]. At the moment, we think this is a side effect. It is difficult to defend yourself physically. These waves are still traveling – it's physics. Estonia can turn to the International Telecommunication Union, of which our eastern neighbor is also a member. Or we can also approach our eastern neighbor directly regarding this problem. However, in general, these types of approaches have not been very successful," Kulu said.

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