Three years ago, LFV, which provides air navigation services for civil and military aviation in Sweden, received only a few reports of planes flying without their transponders switched on. Last year, there were 29 instances reported, and this year, there have been eight to nine cases, according to LFV.
"Rather often, these have been Russian planes," says Olle Sundin, the director general of LFV. "There are also NATO planes, but the ones without transponders have primarily been Russian planes that have carried out signals intelligence."
He noted that since Russia began increasing armaments, they have noticed a lot of transponder-less air traffic flying from the direction of Estonia and Finland, and then continuing down alongside Gotland and over the southern Baltic.
Transponders send out precise information about a plane's location. In international air space, it is permitted to fly without sending out this information, but ethical rules demand that military planes make way for civil flight traffic. Sundin says most agree that good ethics were not exercised in the air space over international waters in the majority of instances last year.
Defense Minister Peter Hultqvist (Social Democrats) told Swedish Radio News on Tuesday that he will bring up the issue at a NATO summit in Warsaw later this week. Even though Sweden does not belong to the military alliance, it is a partner country, and has thus been invited to participate.
"This type of unprofessional behavior, when one flies very close and provocatively, is something I mainly blame Russia for," Hultqvist says.
This text has been corrected. A previous version stated that the number of planes discovered to have been flying with their transponders off has so far this year been as many as the total in 2015. That is incorrect. This year so far, there have been 8-9 such cases, however, that is an increase compared to 2014, which saw just 5 cases.