1961. The following incident has been reported by several investigators as Alberto Fenoglio, in 1962, British researcher Derek Mansell, in 1965, and the UK UFO magazine Flying Saucer Review in 1967.
The details differ some, very little, but the main story is intact and very intriguing.
An Antonov An-2P, a small transport plane, left an airfield at or near Sverdlovsk, Russia, bound for Kurgan, with 4 people aboard, Mansell's report says 7, mail and luggage. After flying about 85 miles, and after the pilot has communicated with the ground control, the plane disappeared from the radar screen.
A search was launched with helicopters and troops, and as the pilot had given a position just moments before the plane vanished, it was found after only two days at the area of Tobelak, Siberia. The plane was found in a small clearing in the forest, too small to have landed there, and it was seemed to have been put down from above gently.
No passenger and pilot was to be found, or ever since. All mail was intact and the motor had fuel for another 2 hours of flight and ran fine.
This event is very similar to the disappearance of an American B-52 incident during the Vietnam war in the 1970s.