The An-32 is a Soviet-designed twin engine turboprop transport aircraft used extensively by the Air Force

The search for the Indian Air Force's missing An-32 aircraft entered its fourth day today, prompting the deployment of an Unmanned Aerial Vehicles (UAV). In addition, two Cheetah helicopters, to be used to access areas that can't be reached by larger helicopters, will be pressed into service tomorrow.

The missing An-32, which was carrying 13 people and took off from Jorhat in Assam on Monday, was last in contact at 1 pm, sources told NDTV.

Arunachal Pradesh Chief Minister Pema Khandu has called on district administrations of Siang, West Siang, Lower Siang and Shi-Yomi to intensify their operations.

The district collectors of these areas are working closely with the Air Force to help with all possible means, a statement by the Chief Minister's Office said. The state government has also asked district administration officials and locals to carry out ground searches on a war footing.

The Air Force has also deployed Mi-17 and ALH helicopters, as well as a C-130J plane. ISRO satellites have also been engaged in the search operation. This brings the total number of aircraft involved in the operation to 13 and includes two Sukhoi Su-30 fighter jets.

The search area is centred on the Bayor Adi mountain range, which lies in front of Tumbin village, the Pari Adi mountain range in front of Molo village and the Sibir-Virgong mountain range between those two villages. All these ranges fall under the Kaying and Payum administrative circle and were on the aircraft's planned route.

Earlier today, Mr Khandu had said villagers living in Tumbin "saw thick black smoke" and that their statements were being verified.

"... three persons of Tumbin village stated that on that day and time they saw thick black smoke which was originating from a mountain about 7-8 km towards Molo village," he said.

As yet no signal from the plane's Search and Rescue Beacon, which has not been in production for 14 years, has been detected.

This distress signal was meant to have been picked up by a satellite belonging to Cospas-Sarsat, an international satellite-aided search and rescue facility. Additionally, a distress signal would also have been heard by search aircraft which had tuned into 243 MHz, the international air distress frequency.

The An-32 is a Soviet-designed twin engine turboprop transport aircraft that has been used extensively by the Air Force for over four decades. Since it joined the IAF fleet, the rugged planes used to ferry people and air-drop supplies have undergone several rounds of upgrades.