Aeroflot Flight 1661
An Antonov An-24 similar to the accident aircraft
|Date||1 April 1970|
|Summary||Collision with weather balloon|
|Site||20 km southeast of Toguchin|
|Aircraft type||Antonov An-24B|
|Flight origin||Tolmachevo Airport, Ob|
|Stopover||Yemelyanovo International Airport, Krasnoyarsk|
Aeroflot Flight 1661 was a passenger flight operated by an Antonov An-24 that crashed during initial climb 25 minutes after take off from Tolmachevo Airport on 1 April 1970, resulting in the death of all 45 people on board. An investigation revealed that the Antonov collided with a radiosonde causing a loss of control.
Flight 1661 was a scheduled domestic flight from Novosibirsk to Bratsk with an intermediate stop at Krasnoyarsk. At 03:42 local time the An-24 departed Tolmachevo Airport from runway 25 on a heading of 251 degrees. Shortly after take off the aircraft made a turn to the left and at 03:53 contacted air traffic control (ATC) and reported their altitude as 4,200 meters and received clearance to continue climbing to 6,000 meters. At 04:10 ATC attempted to contact flight 1661 but no further transmissions from the Antonov were received.
At a distance of 131 km from the departure airport while ascending through 5,400 meters the aircraft's nose cone collided with a radiosonde destroying the aircraft's weather radar and damaging the cockpit. Out of control, the Antonov nosed over and began to descend rapidly. At an altitude of 2,000 meters and a speed of 700 km/h the wing and horizontal stabilizer separated from the aircraft due to aerodynamic forces well beyond its design limits. The fuselage then continued 2.5 km before striking the ground at 300 km/h and a vertical speed of 60 meters per second. The flight duration was 25 minutes, 25 seconds and the crash site was in a farm field approximately 142 km from Tolmachevo Airport.
The Antonov An-24 involved was serial number 79901204 and registered as CCCP-47751 to Aeroflot. The construction of the airliner was completed in 1967 and it had sustained a total of 3,975 flight hours and 3,832 takeoff and landing cycles at the time of the crash.
Investigators examining the crash site discovered unusual damage to the aircraft's radome and nose structure and that a substantial portion of the windshield was missing. Also found among the wreckage were parts of two radiosondes of the type then being used by the Federal Service for Hydrometeorology and Environmental Monitoring of Russia for the monitoring of meteorological conditions. Investigators also discovered parts of the aircraft's nose cone six km away from the site of the fuselage crash and these components displayed evidence of collision with a solid object. Officials concluded that the cause of the accident was collision in flight with a foreign object (radiosonde/balloon assembly).
- "An-24B catastrophe of the West-Siberian UGA in the Toguchin area". airdisaster.ru (in Russian). Retrieved 2018-07-21.
- "Accident description Wednesday 1 April 1970". aviation-safety.net. Retrieved 2018-07-21.
- "Accident Details April 1, 1970". planecrashinfo.com. Retrieved 2018-07-21.