Preliminary information indicates that the KD-Avia Boeing 737-300 which performed a gear-up landing at Kaliningrad on 1 October had aborted its initial approach because of a flap problem.
Russia's federal air transport authority Rosaviatsia states that, at 22:02, as the jet approached Kaliningrad's Khrabrovo Airport from Barcelona, the crew reported the aircraft's flaps had not deployed.
The 737 aborted the approach and began circling for a second attempt and, at 22:06, the crew advised that the flaps had extended.
Emergency services were alerted at 22:15 to prepare for the aircraft's arrival. The jet landed, with its undercarriage retracted, three minutes later.
Neither Rosaviatsia nor the Russian Interstate Aviation Committee (MAK) has given any indication as to the reason why the 737's gear was not lowered.
Although the accident badly damaged the aircraft and resulted in the closure of the airport for several hours, none of the 144 passengers and crew was injured.