Pilot error could be the cause of the plane crash on Saturday (April 10), which killed Polish president Lech Kaczynski.
Preliminary investigations by the Russian government into the incident have ruled out technical error and are concentrating on the pilot's decision to land in thick fog, despite warnings not to do so.
The Polish military plane, a soviet-designed Tupolev 154 that was more than 20 years old, crashed into trees near Smolensk Airport, killing everyone on board.
Russian prime minister Vladimir Putin has said he will oversee the investigation into the crash.