Defence authorities on Thursday recovered the cockpit voice and flight data recorder, commonly known as black box, of the helicopter that crashed near Tamil Nadu’s Coonoor town on Wednesday killing Chief of Defence Staff Bipin Rawat and 12 others, The Hindu reported.

Recordings retrieved from the black box could be helpful in ascertaining the reason of the crash.

The chief of defence staff’s wife Madhulika Rawat was also among the casualties, as 13 of the 14 people on board the Indian Air Force helicopter died in the accident. The only survivor, Air Force group Captain Varun Singh is on life support and being treated for injuries.

On Thursday evening, Singh was moved to Command Hospital in Bengaluru for treatment, reported ANI.

Unidentified defence officials said that the black box was found after authorities increased the area of the search operation from 300 metres to one kilometre from the site of the crash, PTI reported.

The Army has restricted civilian access to the area from where the black box was retrieved, PTI reported.

The severity of the crash has made it difficult to establish identities of those who died, the Indian Army has said. But the authorities are taking all possible steps to ensure the process, keeping in mind the emotional state of the families, ANI reported, citing a statement.

“Close family members of all the deceased personnel are arriving at Delhi,” the statement read. “All necessary assistance and support are being provided.”

Meanwhile, Union Defence Minister Rajnath Singh on Thursday told Parliament that the Indian Air Force has ordered a tri-service inquiry into the helicopter crash.

Group Captain Singh’s father, Colonel (retired) KP Singh said that his son will be shifted to Bengaluru from Military Hospital in Tamil Nadu’s Wellington, according to PTI. He added that he could not say anything about his son’s condition as he was not sure.