The first analysis of flight recorders from the Polish plane that crashed in Russia killing President Lech Kaczynski and 95 others show pilot error was a cause, a report said on Thursday.
"An analysis of the evidence, including the first results from the decoding of the black boxes, shows that an error in piloting led to the disaster," Russia's Interfax news agency quoted a source close to the investigation as saying.
Russian officials have already ruled out fire or explosion as a cause of the crash on Saturday at Severny military airport outside the western Russian city of Smolensk. The plane was attempting to land in thick fog and hit tree tops.
Almost a week after the catastrophe, numerous questions remain about the direct cause of the crash, which air traffic controllers said came after the crew repeatedly ignored advice to land at another airport.
The source, who was not named, told Interfax it was possible that the Polish crew of the Russian-made Tu-154 were not aware of the particularities of the plane when they repeatedly tried to land in bad weather.
The official said it appeared that on its final attempt, the plane tried to land by levelling out from its oblique descent approach to a horizontal angle in a bid to compensate for the bad weather.
{{/usCountry}}The official said it appeared that on its final attempt, the plane tried to land by levelling out from its oblique descent approach to a horizontal angle in a bid to compensate for the bad weather.
{{/usCountry}}"A particularity of the plane is that if its speed of descent is more that six metres per second, when the plane equalized and goes into a horizontal flight it loses altitude," the source said.
"That means that it loses altitude much quicker than usual."
Interfax said two of the black boxes found at the scene of the crash were being examined by Russian and Polish investigators at a defence ministry investigation centre in the Moscow region.
A third, which had been installed in the plane by its Polish owners, is being examined in Poland. The other two has been installed by the Russian manufacturers.
Kaczynski and the presidential delegation were killed as they were heading to a memorial service at Katyn, near Smolensk, for 22,000 Polish officers and troops killed by Soviet forces in World War II 70 years ago.