CDS' chopper crash caused by pilots' misjudgment: Report

Sudden weather change led to pilots; spatial disorientation: Court of Inquiry

A tri-service Court of Inquiry has submitted its preliminary findings into the Mi-17 V5 helicopter crash that killed the Chief of Defence Staff (CDS), General Bipin Rawat, and 12 others on December 8.

According to a Ministry of Defence (MoD) statement on Friday, “The inquiry team analysed the Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR), besides questioning all available witnesses to determine the most probable cause of the accident.”

“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. This led to spatial disorientation of the pilot resulting in Controlled Flight into Terrain (CFIT),” said the Court of Inquiry.

CFIT, is the bleak term used to describe an aircraft impacting the ground while the pilot(s) are in full control of the machine.

Spatial disorientation is the inability of a pilot to correctly interpret an aircraft’s attitude, altitude or airspeed in relation to the earth or other points of reference. It is most critical at night, or in poor weather, when there is no visible horizon, since vision is the dominant sense for orientation.

For example, a pilot flying over snow with the sky obscured, loses his/her perception of depth. Or a pilot flying in cloud, or in poor weather conditions when the horizon is not visible, may feel he is banking to the left or right when he is actually flying straight and level. This could lead to over-correction, which could be disastrous if the pilot does not recover in time.

According to Wing Commander Abdul Naseer Hanfee, a decorated helicopter pilot who has extensive experience flying the Mi-17 helicopter in the Nilgiri mountains, where the crash occurred, there is often a huge build-up of moisture in those hills that builds up into clouds when the temperature rises.   When helicopter pilots try to fly through those clouds, they get spatially disoriented, resulting in their crashing into the ground.

Experienced pilots, such as the two who were flying that helicopter, would return to their home base in Sulur, outside Coimbatore and return when the clouds dissipated somewhat. The inquiry has not mentioned why the pilots did not do so.  

Lessons will be learned from this accident, said Hanfee. That is also evident from the MoD release, which states: “Based on its findings, the Court of Inquiry has made certain recommendations which are being reviewed.”