Remembering Aeroflot Flight 6551

Aeroflot Flight 6551, a scheduled domestic passenger flight on an Ilyushin Il-18B from Baku (GYD/UBBB) to Novosibirsk (OVB/UNNT) with a stopover in Tashkent (TAS/UTTT), crashed on the 11th of May 1973, over Semipalatinsk in the Kazakh SSR, resulting in the death of all 63 people on board.

While on autopilot, the aircraft's speed dropped from 400 to 370 km/h within six seconds at cruising altitude, followed by a rapid descent without lateral roll, experiencing overloads between 1.5 to -0.8g. Seventeen seconds later, the plane entered a right bank with an angular velocity exceeding 100 degrees per second. This led to overloads that caused the right wing to detach at 5,000 meters (16,000 ft) and a speed of 670 km/h, followed by the fuselage breaking apart at 3,600 meters (11,800 ft) and a speed of 700 km/h, surpassing the Il-18's maximum safe speed.

The aircraft's wreckage impacted the steppe 84 kilometers (52 miles; 45 nautical miles) south of Semipalatinsk at 04:37 local time, 38 seconds after the descent began. Although investigators reached the crash site by 04:50 local time, there were no survivors.

Military units in the vicinity reported no projectiles fired or air force operations that could have interfered with the flight at the crash time. The initial phase of the descent suggested a controlled emergency altitude reduction, but this was followed by an unexplained loss of control, leading to an overspeed condition. One hypothesis was an accidental elevator control loss by a crew member during the emergency descent, but this could not be definitively established.

Aircraft Information:

Aircraft: Aeroflot

Code: SU/AFL

Aircraft: Ilyushin Il-18B

Registration: CCCP-75687

Serial Number: 189001202

Engines:  Ivchenko AI-20

First Flew: 1959

Age: 14 years