The 1971 Surgut Aeroflot Antonov An-12 crash occurred on 22 January 1971, when an Aeroflot

Aeroflot

OJSC AeroflotRussian Airlines , commonly known as Aeroflot , is the flag carrier and largest airline of the Russian Federation, based on passengers carried per year...

 Antonov An-12B

Antonov An-12

The Antonov An-12 is a four-engined turboprop transport aircraft designed in the Soviet Union. It is the military version of the Antonov An-10.-Design and development:...

, registered

Aircraft registration

An aircraft registration is a unique alphanumeric string that identifies a civil aircraft, in similar fashion to a licence plate on an automobile...

 CCCP-11000, flying from Tsentralny Airport

Tsentralny Airport

-New Fedorova airport:A new airport is built at Fedorova, North-West of Omsk. As of 2010, construction is stalled.-External links:*...

, Omsk

Omsk

-History:The wooden fort of Omsk was erected in 1716 to protect the expanding Russian frontier along the Ishim and the Irtysh rivers against the Kyrgyz nomads of the Steppes...

, Russia

Russia

Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

, crashed 15km short of the runway on approach to Surgut International Airport, Surgut

Surgut

Surgut is a city in Khanty-Mansi Autonomous Okrug, Russia, located on the Ob River near its junction with the Irtysh River, the largest in the autonomous okrug and the second largest in Tyumen Oblast. Population:...

, Russia. An investigation found the aircraft's ice protection system was ineffective because the engine bleed air

Bleed air

Bleed air in gas turbine engines is compressed air taken from within the engine, after the compressor stage and before the fuel is injected in the burners. While in theory bleed air could be drawn in any gas turbine engine, its usage is generally restricted to jet engines used in aircraft...

 valves were closed during the flight; ice

Ice

Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...

therefore built up on the aircraft causing it to go out of control.