A matter of "concern" is that the Emergency Locator Transmitter (ELT) on the aircraft did not function which has made the search operation very tough.
"It is very unfortunate that we have not been able to trace the missing aircraft and the personnel on board. It is a very difficult moment for all of us and we share the concerns of the distraught family members," chief of the Indian Air Force Air Chief Marshal Arup Raha said in New Delhi.
Amid criticism in some quarters about the existing over 100 AN 32 aircraft and how they have outrun their life, Raha sought to defend it saying in the last three decades of its operations, IAF has exploited the capabilities of this aircraft as the workhorse of the force.
The missing AN-32 transport aircraft, which was inducted into the IAF between 1984-1991, had last year undergone a major refit.
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"Because of its excellent operational performance, AN-32 has been landing at Daulat Beg Oldie, which is the highest landing ground in the world. Needless to say that capable aircrew are chosen to fly these aircraft," he said.
"A thorough enquiry will be conducted to ascertain exactly what led to this unfortunate event. The IAF remains committed to provide the best possible equipment and training to our personnel so that they can execute their assigned missions professionally," he said in a statement.
Navy Chief Admiral Sunil Lanba said in New Delhi that 13 ships from the Navy and four Coast Guard ships along with 18 aircraft, which have done a total of over 250 hours of sorties, are engaged in the search and rescue operation.
Bargotra said that during the last four days, the area of search operation had been extended and "we are looking on all directions."
Stating that a linear search was conducted side by side, he said,"we are picking up some items but they don't belong to the aircraft. Presently the search is continuous."
Referring to absence of beacons from the Emergency
Locator Transmitter (ELT) of the aircraft, Bargotra said signals from it would have made the rescue task much easier.
"Even in the Coast Guard Dornier accident, ELT did not operate. Prior to that there was another Dornier of the Indian Navy, in that also ELT did not operate. It is a matter of concern which has been taken up with the equipment manufacturer and they will be looking into it.
"Yes, it is a fact that in more than one case, ELT did not operate," the official said.
He said the next step would be to go in for underwater search after surface level searches, adding it was not very simple.
Replying to a question, Bargotra said they had enough resources to undertake the operations, adding the search area had been expanded from the initial 14,400 square nautical miles.
Raha said radar contact with the aircraft was lost when the aircraft was east of Chennai at an approximate distance of 270 km. Since then there has been no contact with the aircraft, he added.