On April 3, 1966, 5 Soviet crews of the 668th Aviation Regiment of the Soviet Forces Group in Germany were ordered to transfer Yak-28P aircraft from Novosibirsk to the airfield of Köthen (GDR). All planes were unexpectedly landed at an intermediate airfield in Finov, not flying to Köthen 15 minutes. Kapustin and Yanov's crew was serving in this city.

Kapustin's widow recalled that Boris Vladislavovich himself spoke then about the malfunction of one of the airplanes. For almost 3 days the technicians tried to fix the engines. Finally, on April 6, all 5 crews flew to their destination. The day was overcast, the sky was covered with clouds. On the 12th minute of the flight at an altitude of 4000 meters in the plane of Kapustin and Yanov's crew both engines failed. From the command post came the order to eject. But the pilots decided to break through the clouds and find out the situation. Having made a maneuver, they saw under them densely populated Berlin. Immediately it was decided to take the plane away from the city and land it in a clearing. But altitude and speed were lost, and a dam and a cemetery suddenly appeared on the way. On April 6, 1966, Easter was celebrated in Germany, and the cemetery was crowded.

Boris Kapustin gave the navigator the order to eject and decided to steer the falling plane away from the crowds. However, Yanov refused to abandon his comrade.

An eyewitness to the events, Jürgen Schrader, who was working at the construction site that day, described the events as follows: an airplane suddenly emerged from under the clouds with a plume of smoke trailing behind it. It moved in jerks, apparently the pilots were desperately trying to start the engines. The plane passed over two residential high-rise buildings, almost brushing the fuselage on the antennas on the roof. Eyewitnesses noted that by inhuman efforts the plane lifted off and circled the dam and the cemetery. After that it fell into the lake Stössensee with a stone, burrowing into the silt for 2 meters. A German pilot who happened to observe the maneuver said: "...He did the impossible..."

For twenty-four hours the British (the plane went down in their sector of West Berlin) refused to indicate the place of the crash. And when the bodies of the pilots and the fighter were handed over to the Soviet side, it turned out that the aircraft's secret technical developments had been dismantled. As a result, the declassified Yak-28P did not go into production and was not adopted into service as planned.

It was for this reason that the pilots were posthumously awarded the Order of the Red Banner, and not awarded the title of Heroes of the Soviet Union (as follows from the response of the Ministry of Defense to the pioneers of School No. 75 in Rostov-on-Don). The secret fighter plane fell into the hands of the potential enemy, who modernized its aviation at the expense of this.