The Army on Saturday said that the crew members on board of the Advanced Light Helicopter (ALH) had made a "Mayday" call to the Air Traffic Control (ATC), suggesting a mechanical or technical fault just before the chopper crashed near Tuting in Arunachal Pradesh on Friday.
"Prior to the crash, the ATC had received a MAY DAY call suggesting a technical or mechanical failure. This will form the focus of the Court of Inquiry, which has been immediately constituted to investigate the causes of the accident," said a statement issued by the Army on Saturday morning.
A Mayday message is sent to an ATC to seek help in case of a difficult situation in a helicopter or an aircraft.
The Army said the weather was good for flying operations and the pilots were experienced but the terrain was "extremely challenging" having hills with steep gradients and thick jungle.
The search and rescue operation ended on Saturday with the recovery of bodies of all five Armymen from the crash site at Migging village, South of Tuting, the headquarters of Upper Siang district. The deceased included two Majors--Vikas Bhambhu and Mustafa Bohara. The three others were identified as Aswin KV, Biresh Sinha and Rohitashva Kumar.
The ALH with Weapons System Integrated based at Likabali military station in Lower Siang district had taken off with five on board for a routine sortie. It, however, crashed at 10.43am. The indigenously designed ALH was inducted into service in June 2015 in order to add teeth to the Armymen guarding the border with China.
The place where the ALH crashed is 35km from the border with China, Army sources said.
"Immediate joint search operations with teams from the Army and Air Force located the crash site, where the terrain is extremely challenging in terms of hills with steep gradients and thick jungle. It is reported that the weather was good for flying operations. The pilots had more than 600 combined flying hours on ALH-WSI and over 1800 service flying hours between them," said the statement.
This was the second helicopter mishap in Arunachal Pradesh this month. On October 5, a Cheetah helicopter used by the Army crashed near Tawang in which a Lt. Colonel died and another was injured.