Chennai/New Delhi: The search for the Indian Air Force (IAF) AN-32 aircraft that went missing on is seriously hampered as there are no signals from the emergency locator transmitter (ELT) fixed in the plane, said a senior Indian Coast Guard official. He also said the search would continue underwater if no debris is found on the sea surface. "There are no signals from the ELT of the ill-fated plane. Similarly the ELT of the Coast Guard's Dornier aircraft which went down into the Bay of Bengal last year did not emit out any signals," Coast Guard Region (East) Commander, Inspector General Rajan Bargotra told reporters in Chennai on Monday. "It is a serious concern and the matter will be taken up with the aircraft manufacturers," he said. An experienced pilot in Indian defence forces told IANS that maintenance of this equipment is an issue. The aircraft with 29 people onboard went off the radar on July 22nd morning over the Bay of Bengal half an hour after take off from Chennai on its journey to Port Blair. To a query, Bargotra said the search for the missing plane will continue even it is is going to be a prolonged one. "We have requested the National Institute of Ocean Technology (NIOT) for their vessel for the search operations," he added. While sources said satellites have provided some hints, and the areas indicated are being searched, no debris or signals from the aircraft could be spotted. Indian Navy chief, Admiral Sunil Lanba, meanwhile, said a total 250 hours of sorties have been flown in search of the plane, and all leads found are being followed. "The coordinated efforts between Indian Navy, IAF (Indian Air Force) and Coast Guard is continuing. All together 17 ships and 17-18 aircraft are searching designated areas. Over 250 hours of sorties have been flown," he said. "We have got inputs from satellite images and also from sensors of the aircraft. All leads have been followed. It is an ongoing search at the moment," the Navy chief said. "We have also kept close liaison with families of all on board. We are keeping them in the loop and informing them how the search is progressing," he added. The navy has pressed a flotilla of vessels including a submarine to locate the missing aircraft. The aircraft, an upgraded AN-32 belonging to 33 Squadron, took off from Tambaram Air Force Station in Chennai at 8.30 a.m. and was expected to land at Port Blair at 11.30 a.m. The recorded transcript of Chennai air traffic radar showed the last pickup of the aircraft was 151 nautical miles east of Chennai when it was observed to have carried out a left turn with rapid loss of height from 23,000 feet.