The business jet believed to have carried Yevgeny V. Prigozhin, the Wagner mercenary group leader, was flying at a constant speed and altitude until it plummeted, flight-tracking data shows.

Flightradar24, a website tracking real-time aircraft information, said in a report published on Wednesday that the Embraer Legacy 600 jet reached a cruising altitude of 28,000 feet at 6:10pm Moscow time and flew at the same altitude for the next nine minutes, showing no signs of problems.

The aircraft then made erratic ascents and descents of several hundred feet in the space of about 12 seconds before suddenly dropping some 8,000 feet for about 20 seconds. When the jet last transmitted data, at about 6:20pm, it was flying at 19,725 feet.

“It is this data that provides some insight into the final moments of the flight,” Flightradar24 said, noting that it showed a “dramatic descent”.

The plane’s sudden plunge was also captured in an unconfirmed video released by Russian state media that appeared to show it rapidly falling nose-first from the sky, leaving a plume of smoke behind.

Chris Lomas, an aviation content specialist for Flightradar24, said it was impossible to determine the cause of the crash. But he confirmed that the plane had first cruised “apparently without any issue” before plummeting.

Lomas said that the jet’s brief ascents and descents may have been a sign of “an attempt to respond in some way” to the event that eventually led the plane to crash.

Embraer, the Brazilian maker of the Legacy 600 private jet linked to Prigozhin, said that it had stopped providing any support for the aircraft in 2019 because of sanctions. That support is largely maintenance-related and can potentially include data monitoring.

New York Times News Service