"When information came from Eurocontrol that the aircraft has no right to land in the EU, it was already in Lithuanian airspace," Julija Ciziene, a communication officer at the Strategic Development and International Programs Division of the state-owned air navigation service provider Oro Navigacija (Air Navigation), told BNS.

"The Lithuanian Traffic Control Center instructed the aircraft to return to the place of departure, but it did not have enough fuel to do so. The aircraft was allowed to land at Vilnius Airport for safety reasons," Ciziene said.

"Eurocontrol administers the so-called 'blacklist' and monitors (flights) to ensure that planes on that list do not fly within EU airspace," she added.

The Mi-8 helicopter is owned by Moldova-registered Valan International Cargo Charter. The European Commission last April banned the carrier's aircraft from entering EU airspace due to the Moldovan Civil Aviation Administration's failure "to implement and enforce the applicable international safety standards".

Some other air carriers certified in Moldova are also subject to the ban.

According to Oro Navigacija, the Mi-8 helicopter was on its way from St. Petersburg to Vilnius. Flight controllers did not know it was a blacklisted aircraft until it switched from visual flight rules (VFR) to instrument flight rules (IFR).

If a flight is operated under VFR, no flight plan is submitted to Eurocontrol, Ciziene said

"It was only after the aircraft switched to IFT that we were informed about the ban by the Latvian Air Traffic Control Center, which in turn had received that information from Eurocontrol," she said.

Oro Navigacija says it does not know why the helicopter switched to IFT.

Alvydas Sumskas, the head of the Civil Aviation Department at the Transport Competence Agency, says that if the aircraft had not changed the rules, traffic controllers would have not known that it is banned from flying in EU airspace.

"There are gaps in the monitoring system (...). This is an exceptional case that apparently needs to be given thought. This is not a Lithuanian problem, because the helicopter flew through Estonian airspace without any reaction and then did the same in Latvian airspace," he said.

The Lithuanian Transport Ministry says it will submit proposals both to the European Commission and to Eurocontrol, suggesting that all flights, operated both under VFR and IFR, should be monitored.

"The key question in this situation is how the aircraft crossed into Estonian airspace from Russia and then into Latvia and Lithuania," Deputy Transport Minister Vladislav Kondratovic told BNS.

"The Transport Ministry has already informed Eurocontrol about the need to improve the exchange of information to prevent such situations," the official said.

"The ministry will also continue discussions with Eurocontrol and with the European Commission in the near future in an effort to find solutions as to how improve the systems and procedures reporting EU airspace entries by blacklisted aircraft," he added.

Six Moldovan citizens who were aboard the Mi-8 helicopter that landed in Vilnius were allowed by border guards to stay in Lithuania, because Moldavians do not need visas to enter the country.