The 8 December Mi-17V5 crash in which India's first chief of defence staff (CDS) General Bipin Rawat was killed along with 13 others took place due to spatial disorientation of the pilot in bad weather, the Indian Air Force (IAF) said on Friday in its first official statement on the accident.
"The accident was a result of (the chopper's) 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)," the statement said, referring to the preliminary findings of a tri-services probe.
Hindustan Times reported on January 5 that the crash was most likely a CFIT accident with cloudy weather a contributory factor.
In aviation parlance, CFIT refers to the accidental collision with terrain of an airworthy aircraft under the flight crew's full control. In such accidents, the pilot or crew is unaware of the looming danger until it is too late. Loss of situational awareness is a major factor leading to CFIT accidents, as previously reported.
The probe ruled out negligence.
The court of inquiry has ruled out mechanical failure, sabotage or negligence as a cause of the accident, the air force said.
"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 added. The recommendations made by the court of inquiry to prevent such accidents are being reviewed.
IAF on January 5 made a detailed presentation to defence minister Rajnath Singh on the inquiry report into the Mi-17V5 accident.
The Russian-origin helicopter, considered extremely safe and reliable, was fully serviceable when it crashed near Coonoor. The low-flying helicopter flew into a cloud cover seconds before it went down in a fireball, barely seven minutes before it was scheduled to land in Wellington.
The helicopter took off from the Sulur air base at 11.48am and was scheduled to land at the helipad at the Wellington golf course at 12.15pm. The air traffic control at Sulur, however, lost contact with the helicopter at 12.08pm, 20 minutes after it took off.
IAF is expected to review protocols governing flights ferrying important people. Rawat was on a visit to the Defence Services Staff College (DSSC) at Wellington to deliver a talk when the Mi-17V5 crashed.
Those killed in the crash included the CDS's wife Madhulika Raje Singh Rawat, his defence assistant Brigadier LS Lidder, Lieutenant Colonel Harjinder Singh, Wing Commander Prithvi Singh Chauhan, the pilot of the Mi-17V5, Squadron Leader Kuldeep Singh, the co-pilot, Junior Warrant Officer Rana Pratap Das, Junior Warrant Officer Arakkal Pradeep, Havildar Satpal Rai, Naik Gursewak Singh, Naik Jitendra Kumar, Lance Naik Vivek Kumar and Lance Naik B Sai Teja.
The sole survivor of the crash, Group Captain Varun Singh, breathed his last on December 15 after putting up a week-long fight against death.
Developed by Russian Helicopters, the Mi-17V5 is designed to carry personnel, cargo and equipment. The Mi-17V5 can carry a load of around four tonnes in a full cargo role. It can also insert assault forces behind the enemy lines, a role frequently demonstrated by the IAF during military exercises.
The helicopter is equipped with modern avionics, a self-defence system and other advanced features that enhance its survivability. The Mi-17V5, which has an armoured cockpit, can be fitted with rockets, cannons and small arms for carrying out offensive roles. It has a service ceiling of 6,000 metre, top speed of 250 kmph and a maximum range of around 1,180 km with additional fuel tanks.