The Army has launched a search operation to find out the Black Box of the Advanced Light Helicopter (ALH) that crashed in Arunachal Pradesh on Friday killing five personnel, officials said.

The Black Box is an instrument that records all flight information which could help ascertain the reason for the crash.

Personnel of 21 Para (Special Force) from Jorhat in Assam, were airdropped at the crash site near Migging, around 35 kilometres from the border with China, on Saturday to recover the Black Box.

The area is thickly wooded which is creating hindrances in searching for the Black Box, an official said on Sunday.

The ALH, carrying five Army personnel including two pilots, was on regular sorties when it crashed at 10.43 am on Friday.

The bodies of four personnel were recovered on Friday evening from the crash site in a densely wooded mountainous area, while the fifth body was found the next day.

Prior to the crash, the Air Traffic Control (ATC) had received a mayday call from the pilots of the ALH suggesting a technical or mechanical failure, defence spokesperson Lt Col A S Walia said.

Mayday' is the word used across the world to make a distress call over radio communication in case of emergency, usually on a ship or aircraft.

The Army headquarters ordered a Court of Inquiry to investigate the cause of the crash.

According to officials, the weather was good for flying operations on Friday and the two pilots had a combined experience of flying for more than 1,800 hours.

The Army helicopter, also known as HAL Rudra, had taken off from Likabali in Lower Siang district.

The HAL Rudra is an attack helicopter manufactured by Hindustan Aeronautics Limited (HAL) for the Indian Army. It is a weapon system integrated (WSI) Mk-IV variant of the Dhruv ALH and is the first armed helicopter produced indigenously in India.

This is the second accident involving an Army helicopter in Arunachal Pradesh this month.

A Cheetah helicopter crashed in Tawang district on October 5 and claimed the life of one of its two pilots.

According to official records, Arunachal Pradesh has witnessed 13 crashes since 1995, and 47 people were killed in them.