Chennai, Dec 9 (IANS): The search for the black box or the flight data recorder of the ill-fated Mi-17V5 helicopter that crashed killing Chief of Defence Staff General Bipin Rawat and 12 other persons near Coonoor in Tamil Nadu, continued on Thursday.

It is learnt the search radius has been increased.

The black box can reveal the data about the helicopter's final flight situation and other aspects.

Though called black box, the flight data recorder is painted a bright orange colour and it records the flight data and cockpit conversations.

Further forensic examination of the remains of the chopper can also reveal if there were external causes for the accident.

In addition, Group Captain Varun Singh, the Directing Staff at the Defence Services Staff College in Wellington, Tamil Nadu, and the lone survivor of the ill-fated chopper, can also provide first hand information on the flight.

Singh is undergoing treatment at the Military Hospital in Wellington with about 80 per cent burn injuries.

On Wednesday, the IAF helicopter with 14 persons on board, including General Rawat and his wife, took off from Sulur air base and crashed minutes before it was supposed to land at Coonoor.