Seven years after he became the first human being in space, Yuri Gagarin was back in a very ordinary cockpit. On the morning of 27 March 1968 he climbed into a two-seat MiG-15UTI jet trainer at Chkalovsky air base near Moscow, with his instructor Vladimir Seryogin in the other seat. It was a routine training flight. Minutes later the jet plunged into a forest near the town of Kirzhach. Both men were killed.

The man who had orbited the Earth in 108 minutes, and survived a re-entry nobody had tried before, died at 34 in one of the most common jet trainers in the Soviet Air Force. For decades, the question of why has attracted official secrecy, rival investigations and more than a few conspiracy theories.

Back to Flying

After Vostok 1, Gagarin was the most famous man in the Soviet Union, but he remained an Air Force pilot, and in March 1968 he was flying training sorties again. His instructor, Vladimir Seryogin, was no ordinary instructor: a Second World War combat pilot, Hero of the Soviet Union, test pilot at the Soviet Air Force Test Institute and commander of the organisation that prepared cosmonauts for flight.

The MiG-15UTI, the tandem-seat trainer version of the famous Korean War fighter, was the standard Soviet two-seat jet trainer of its era. It was simple and robust, but like any jet, a spin entered too close to the ground left almost no room to recover.

Three Investigations, No Single Answer

The crash was investigated separately by the Air Force, official government commissions and the KGB. According to Jamie Doran and Piers Bizony's biography Starman, the KGB worked not just alongside the Air Force and the commission but against them.

The KGB's report, declassified in 2003, blamed ground staff in part. It said an air-traffic controller had given the crew outdated weather information while conditions deteriorated, and that the jet had flown with external fuel tanks still attached, which the planned exercises did not allow. It concluded that the MiG entered a spin, either after a bird strike or after a sudden move to avoid another aircraft, and that the crew, believing they were higher than they were, could not recover in time.

In April 2011, documents from the 1968 commission set up by the Communist Party's Central Committee were declassified. Its original conclusion was that one of the pilots had manoeuvred sharply to avoid a weather balloon or cloud, leading the jet into a dangerous regime and a stall.

Leonov's Theory

Other explanations have been put forward. In 2005 the original crash investigator suggested that a cabin air vent had been left open, starving the crew of oxygen. A variation published in Air & Space/Smithsonian magazine proposed that the crew spotted the open vent, dived for lower altitude as procedure required, and lost consciousness.

The most vivid account came from cosmonaut Alexei Leonov, the first man to walk in space and a member of a state commission on the crash. He was running parachute training that day and heard two loud booms in the distance. He came to believe that a Sukhoi Su-15 fighter, flying below its minimum altitude in bad weather, had gone supersonic very close to the MiG, and that its wake threw the trainer into a spin.

Leonov said the first boom was the fighter breaking the sound barrier and the second was Gagarin's aircraft hitting the ground. It has never been officially confirmed. In 2007 the Kremlin refused to open a new investigation, saying it saw no reason to.

The Kremlin Wall

The Soviet Union gave both men a state funeral. Their ashes were interred in the walls of the Kremlin, and to this day crews preparing to fly to the International Space Station lay flowers there before launch.

More than half a century later, the exact sequence in the cockpit of that MiG-15UTI is still unknown. What is certain is that the first man in space died doing what he loved most, flying a jet, alongside one of the most experienced pilots in the Soviet Air Force.

Sources: Wikipedia (Yuri Gagarin; Vladimir Seryogin), citing the declassified KGB (2003) and Central Committee commission (2011) findings and Alexei Leonov; Jamie Doran and Piers Bizony, Starman; British Pathé (newsreel).