A Polish report into the 2010 plane crash in Russia that killed President Lech Kaczynski and 95 others says Russian air traffic controllers gave incorrect landing instructions to pilots.
The report also said that the airstrip where the plane crashed near Smolensk, Russia, was badly illuminated and that visibility was bad.
Today's long-awaited report also pointed to many failures by Polish officials.
It said that the pilots lacked proper training to fly the plane, a Tupolev 154. The main pilot was inexperienced, and as the only crew member who spoke much Russian was overwhelmed by the difficult conditions, the report said.
The report is significant, however, because it points to mistakes made by Russians.
In contrast, a Russian report released several months ago put full blame for the tragedy on the Poles, straining ties between the two Slavic nations who already share a difficult history.
Russian investigators said that the Polish pilots faced undue pressure from political officials to try to land the plane in heavy fog.
The Polish report differs on that point, too.
It says it did not find that there was any such pressure and that the pilots were not actually trying to land when they clipped a tree and crashed - they were instead circling the area to try to decide whether they should attempt a landing.