Aeroflot Flight 6551

Aeroflot Azerbaijan Division

Company type	Division of Aeroflot
Industry	Airline
Founded	1959
Headquarters	Baku , Soviet Union
Products	Air transport services
Parent	Aeroflot

Aeroflot Flight 6551 (Russian: Рейс 6551 Аэрофлота Reys 6551 Aeroflota) was a scheduled domestic service operated by an Ilyushin Il-18B, flying from Baku to Novosibirsk with an intermediate stop in Tashkent. On 11 May 1973, the aircraft crashed near Semipalatinsk in the Kazakh SSR, resulting in the loss of all 63 individuals on board.

Aircraft

The accident aircraft was an Ilyushin Il-18B bearing the registration CCCP-75687, operated by Aeroflot’s Azerbaijan division. Manufactured in 1959, it had accumulated a total of 21,663 flight hours and undergone 11,787 pressurization cycles by the time of the incident. Originally configured to accommodate 80 passengers, the cabin was later modified to seat 89.

Crew

File:Экипаж Ил-18 Азербайджанского УГА, 1972 г..jpg

From left to right: Radio operator Dmitry Markin, first officer Yuri Filin, Captain Viktor Loginov, flight engineer Valentin Pershin, and navigator Viktor Filatov; photograph taken at Bina Airport in 1972.

There were eight crew members assigned to this flight. The cockpit team included:

• Captain – Viktor Sergeyevich Loginov
• First Officer – Yuri Aleksandrovich Filin
• Flight Engineer – Valentin Nikolayevich Pershin
• Navigator – Viktor Mikhaylovich Filatov
• Radio Operator – Dmitry Korneyevich Markin

Synopsis

The flight took off from Tashkent Airport on May 10 at 23:25 Moscow time (01:25 local time on May 11), carrying 63 individuals, including three children. After departure, the aircraft maintained a cruising altitude of 7,800 metres (25,600 ft) until 00:56 MSK, when the Almaty Airport regional controller instructed the crew to climb to a flight level of 9,000 metres (30,000 ft) and proceed on a bearing of 43 degrees. The pilots acknowledged this directive and began ascending accordingly. At 01:12 MSK, the crew briefly communicated with the Ayaguz airport controller, and again at 01:22 to report their imminent exit from the Ayaguz sector en route to Semipalatinsk. Upon contacting the Semipalatinsk controller, the flight initiated a descent back to 7,800 metres (25,600 ft) while executing a 360-degree left turn. Radar last detected the aircraft approximately 110 kilometres (68 mi; 59 nmi) from Semipalatinsk; however, it had recently flown within 90 kilometres (56 mi; 49 nmi) of the airport without radar detection. When expected overhead at 01:52 MSK (04:52 local time), attempts by the Semipalatinsk controller to establish contact went unanswered. Weather conditions at that moment included cloud cover between 1,000–1,300 metres (3,300–4,300 ft), light wind and rain, and visibility measured at 10 kilometres (6.2 mi; 5.4 nmi).

During autopilot operation, within a brief six-second interval, the indicated airspeed dropped from 400 to 370 km/h (220 to 200 kn; 250 to 230 mph) while maintaining assigned altitude before entering a rapid descent without lateral roll, experiencing overloads fluctuating between 1.5 and -0.8g. Seventeen seconds later, the aircraft entered a steep right bank with an angular velocity exceeding 100 degrees per second, generating forces that caused the right wing to separate at an altitude of 5,000 metres (16,000 ft) and speed of approximately 670 km/h (360 kn; 420 mph). The fuselage subsequently broke apart at around 3,600 metres (11,800 ft) altitude traveling near 700 km/h (380 kn; 430 mph), surpassing the Il-18’s maximum permitted speed of 675 km/h (364 kn; 419 mph). At 04:37 local time (01:37 Moscow time), just 38 seconds after the onset of the descent, debris impacted the steppe roughly 84 kilometres (52 mi; 45 nmi) south of Semipalatinsk. Rescue teams reached the burning wreckage by 04:50 local time; tragically, all 63 occupants lost their lives.

Conclusions

Investigators interviewed two nearby military units, both confirming no artillery or missile firing occurred around the crash timeframe, nor were any military aircraft operating that might have collided with this flight. The inquiry suggested that the initial reduction in altitude and speed lasting approximately 20–30 seconds resembled a controlled emergency descent; this was followed by an unexplained loss of control culminating in an overspeed event. One hypothesis proposed was that during this emergency descent, a crew member might have inadvertently lost control over an elevator, though definitive proof was lacking. Notably, during the rapid descent preceding the accident, propellers were found feathered; however, it remains unclear whether this action was manually performed by the crew or automatically engaged by the autopilot system.

Examination revealed two circular puncture marks on the fuselage near the rear baggage compartment. The damaged section was recovered for forensic analysis to determine if artillery shells had caused these holes; results indicated they were impact-related from the crash itself, as no explosive residues were detected. Despite retrieving both flight data recorders and much of the wreckage, investigators were unable to establish a precise cause for the accident due to extensive damage limiting data recovery from the recorders.

See also

• List of accidents and incidents involving the Ilyushin Il-18
• Aeroflot Flight 5484
• Aeroflot Flight 630