有說是機械故障，飛行員跳傘。

https://news.az/news/mig-31-fighter-jet-crashes-in-russia-s-lipetsk-region 

A MiG-31 fighter jet crashed in Russia's Lipetsk region on Thursday, with both pilots ejecting safely, News.az reports citing TASS.

"At about 19:20 Moscow time (1620 GMT), a MiG-31 aircraft crashed in the Lipetsk region while approaching for landing after a scheduled training flight. The crew ejected safely, and there is no threat to their lives," the Russian Ministry of Defense was quoted by TASS as saying.

The aircraft reportedly crashed in an uninhabited area and was not carrying any weapons during the flight.