A safety device that warns pilots when they get too close to the ground was switched off on the Polish plane which crashed in Smolensk on April 10th, according to a report by the Russian news agency Interfax.
Ninety-six people, including Polish President Lech Kaczynski, and many top military and civilian leaders, died when the plane plummeted into woods in Russia.
An expert who examined one of the black boxes concluded from the technical data that the Terrain Awareness and Warning System (TAWS) had been turned off, according to Interfax and reported by Polskaweb
The Polish plane crash has been blamed on pilot error.
But the expert said that the fact that the TAWS device had been switched off caused the plane to crash short of a runway in fog.
“The fact that the jet had a TAWS device “opens more questions than it answers,” said John Cox, a former accident investigator, according to USA Today.
The Russian-built Tupolev TU-154 had been equipped last year with a TAWS system, which is made by Universal Avionics Systems of Tucson.
No plane equipped with the TAWS system has crashed since TAWS was introduced in the late 1990s.
The system has been mandatory on commercial planes since 2005,and has reduced crashes due to planes hitting obstacles to virtually zero, reports USA Today.