The country's first Chief of Defence Staff, General Bipin Rawat, his wife Madhulika and 12 armed forces personnel were killed in the crash near Coonoor in Tamil Nadu.
Sharing preliminary findings of the tri-services Court of Inquiry report, the IAF said the chopper crash was a result of entry into clouds due to unexpected change in weather conditions in the valley.
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.
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The Court of Inquiry has ruled out mechanical failure, sabotage or negligence as a cause of the accident.
The accident was a result of entry into clouds due to unexpected change in weather conditions in the valley, which led to spatial disorientation of the pilot.
"Based on its findings, the Court of Inquiry has made certain recommendations which are being reviewed," the IAF said.
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General Rawat was on a visit to the Defence Services Staff College at Wellington in Nilgiri Hills to address the faculty and student officers of the Staff Course.