“Most airports use alternative approach methods, but some airports, such as Tartu, only use methods that require a GPS signal to support them,” said Jari Paajanen, Finnair’s director of operations.

It’s widely used, but yeah I’m surprised that they’re claiming it’s essential for landings. I though ILS used beacons at the airport, with other beacons for the approach.

Edit: ah, OK, this is why:

“Most airports use alternative approach methods, but some airports, such as Tartu, only use methods that require a GPS signal to support them,” said Jari Paajanen, Finnair’s director of operations.

This airport is small. It is only serviced by one commercial flight to one other airport. There are systems that allow for precision landings during poor visibility without GPS, but they are expensive so airports of this size often don’t have them.

Large airports use the Instrument Landing System, which are radio antennas built near the runway which broadcast radio beams along the approach path so the plane can land using their radios even in near zero visibility.

GPS based approaches are often used in small airports because they are much cheaper to use than radio based systems. Airplanes can land visually if conditions are right, but if GPS is needed for the only instrument approach for this airport and the weather isn’t clear, they have to divert.