On 27 March 1968, Yuri Gagarin, the first man to go into space, died together with pilot Vladimir Seryogin during a routine training flight, after the MiG-15 jet fighter they were flying crashed near Novosyolovo in the Soviet Union.

At the site of the crash, various objects were found, such as personal items of the pilots - a pocket edition book with navigation rules and photos of Sergei Korolyov.

[22] The conclusion of the committee was the following: due to the changes in the air environment during the flight (the details were not specified) the crew made an abrupt maneuver resulting in a spin.

[23] A KGB committee did separate research, in order to prove according to "its own line" if any conspiracy, act of terrorism, or any ill intent existed.

[24] The report states that an air-traffic controller provided Gagarin with outdated weather information and that by the time of his flight, conditions had deteriorated significantly.

[5] A similar theory, published in Air & Space magazine, is that the crew detected the open vent and followed procedure by executing a rapid dive to a lower altitude.

There are various speculations for the crash's causes, such as a version that states Gagarin died during the flight, and another where deep political motives were involved.

[30][19][20][31][32] Alexei Leonov, who was also a member of a state commission established to investigate Gagarin's death, was conducting parachute training sessions that day and heard "two loud booms in the distance".

He believes that a Sukhoi Su-15 was flying below its minimum altitude and, "without realizing it because of the terrible weather conditions, [the pilot] passed within 10 or 20 meters of Yuri and Seryogin's plane while breaking the sound barrier".

[33] In a June 2013 interview with Russian television network RT, Leonov said a report on the incident confirmed the presence of a second aircraft, an "unauthorized" Su-15, flying in the area.

However, as a condition of being allowed to discuss the declassified report, Leonov was barred from disclosing the name of the Su-15 pilot who was 80 years old and in poor health as of 2013.

[34] According to the head of the Cosmonaut Training Center from 1963 to 1972, Nikolai Fyodorovich Kuznetsovru, Seryogin was not well at that time: he often vomited and complained of heart pains.

To prevent oxygen starvation, the pilots sharply tried to lower the plane to the level recommended by the instructions (2,000 metres (6,600 ft)), but the rapid drop in pressure caused them to lose consciousness.

[11] Aksyonov's version notes that the crew of Gagarin and Seryogin, having made a mistake in difficult weather conditions, did not orient themselves in the situation, which led to the fall and crash.

[11] Aksyonov believes that the pilots made their message, most likely, after exiting the final figure, at low speed in a calm flight, but still at a fairly high altitude.

The crash was facilitated by a complex meteorological situation (continuous multilayer clouds with a lower edge at an altitude of about 600 metres (2,000 ft)), as well as numerous violations of the requirements of the Flight Operations Manual and the Fighter Aviation Combat Training Course.