The chopper crash that led to Chief of Defence Staff General Bipin Rawat's death in December, was a result of entry into clouds due to unexpected change in weather conditions in the valley i Tamil Nadu. The preliminary finding of the tri-service investigation into the fatal crash has ruled out mechanical failure, sabotage or negligence as the cause of the accident. The change of weather led to spatial disorientation of the pilot resulting in a controlled flight into terrain, said tha IAF statement, issued on Friday. The inquiry team analysed the Flight Data Recorder and Cockpit Voice Recorder besides questioning all available witnesses to determine the most probable cause of the accident, the statement noted. Based on its findings, the Court of Inquiry has made certain recommendations that are being reviewed. Gen Rawat, his wife and 12 others were killed in the tragic crash in Tamil Nadu's Coonoor on December 8 last year.