This is the unbelievable story of how this MFI aircraft, unauthorized, penetrated the defence zones and landed in the Soviet Union. There are certainly many unpublished facts about this incident in the archives of the Swedish Secret Police and the Foreign Affairs.
What is known is that Mr. Glendenberg one day in January 1973 was assisted when rolling out the plane from the hangar in the picture. After refuelling he took off with the official destination of the town Borlänge in central Sweden.

The ATC at Norrköping shortly thereafter was contacted by the Swedish military enquiring about the destination of the plane. It had obviously been detected by radar when passing though the notification area along the Swedish coast. No interceptors were activated by the Swedish Air Force (otherwise a normal action when violating restricted zones).

After having crossed the Baltic Sea the pilot was running short on fuel over Estonia and then landed on a road. He then managed to get some gasoline from a farmer. With this low grade of liquid in the tanks the pilot took off again heading for Riga.
So far the flying must have taken place at a very low altitude, below the Soviet radar coverage but when finally arriving at Riga Mr. Glendenberg was arrested.

The Russians refused to allow Swedish pilots to bring the aircraft home. Instead it arrived by ship partly dismantled.
The Swedish newspapers were speculating about the reason for this unusual flight. Was it a defection? Attempted espionage? Or just craziness? The pilot was quickly sent back to Sweden without usual "trade offs".
Much in this story
has been told to me by Roland Pettersson, here standing by the plane 34 years later.
He was the person that helped roll the plane out of the hangar that day in 1973.
There is surely much more that could be told in this case if you dig into the
archives in Sweden and Russia.