What caused deadly Russian plane crash?

A handout photo provided early on November 18, 2013 by the Russian Emergencies Ministry's press service shows rescuers working at the crash site of a Boeing 737 passenger airliner in the international airport of Russia's Volga city of Kazan. A Boeing 737 operated by a Russian airline crashed yesterday while attempting to land in Kazan, killing all 50 on board, Russia's emergency situations ministry said. AFP PHOTO / RUSSIAN EMERGENCIES MINISTRY 
-- RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / RUSSIAN EMERGENCIES MINISTRY " - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS --HO/AFP/Getty Images
A handout photo provided early on November 18, 2013 by the Russian Emergencies Ministry's press service shows rescuers working at the crash site of a Boeing 737 passenger airliner in the international airport of Russia's Volga city of Kazan. A Boeing 737 operated by a Russian airline crashed yesterday while attempting to land in Kazan, killing all 50 on board, Russia's emergency situations ministry said. AFP PHOTO / RUSSIAN EMERGENCIES MINISTRY 
-- RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / RUSSIAN EMERGENCIES MINISTRY " - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS --HO/AFP/Getty Images

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    What caused deadly Russian plane crash?

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Boeing investigators are headed to Russia to help investigate the crash that killed 50 people. CNN's Phil Black reports.