Popping up in local news the last couple of days. For now, it seems that nobody has the complete picture. Quoting a news article as I'm unable to post links:
An unidentified Beechcraft with its transponder and radio turned off flew in the airspaces of Hungary, Romania, Serbia and Bulgaria on June 8, 2022. According to a press release issued by the Romanian Ministry of National Defense, the aircraft is thought to have taken off in the region of Debrecen, Hungary at approximately 16:30 CET (2:30 pm GMT) with two people onboard.
Eight minutes later the aircraft was intercepted by a pair Hungarian Air Force Saab JAS 39 Gripen fighter jets. According to the release, the aircraft did not respond to attempts to establish radio communication and ignored all visual signals.
At 17.49 the aircraft entered Romanian airspace in the vicinity of Oradea. As per a cross-border agreement between Romania and Hungary, the Hungarian jets continued to accompany the Beechcraft.
Several minutes later, the aircraft was intercepted by two patrolling US Air Force F-16 Fighting Falcons from 86th Feteşti Air Base. Six USAF F-16s were deployed in Romania in early May 2022 as part of an air policing mission. Upon interception, the Hungarian JAS 39s returned to base.
At 18:36 the mission of following the Beechcraft was taken over by two Romanian Air Force F-16s. While being followed, the aircraft entered Serbian airspace for two minutes in an area between Drobeta-Turnu Severin and Korbovo.
At 19:09 the Beechcraft entered Bulgarian airspace, and the Romanian aircraft returned to base.
Also, some sources state the plane might be a Beech, not a Piper. Strange occurrence. They report that the occupants of the aircraft stopped at least once to refuel with jugs stored in the cockpit. Our ministry reports that the aircraft was found at Targovishte's old airport LBTG