Poland said Friday in an investigation that poor lighting at a Russian airport and air traffic control failure are to blame for the air crash in 2011 that killed Former President Lech Kaczynski.

"The commission has established that the lighting systems at the airport were faulty and inadequate," Lieutenant Colonel Robert Benedict told a news conference.

The crew also received wrong orders from the Russian air traffic controller, he said.

The air accident at the Smolensk airport in western Russia also killed Kaczynski's wife Maria and many senior military officials among others.