The AN-32 transport aircraft of the Indian Air Force (IAF), which went missing over the Bay of Bengal on July 22, had no underwater locator beacon (ULB) on it. Lack of this basic safety device is making the work of search teams more difficult.
The ULB usually remains integrated with Flight Data Recorder in the cockpit. Once an aircraft goes underwater, the device starts transmitting signals at ultra-low level frequencies which can travel through water. These can be tracked by submarines and other underwater vessels for over a month, which is the battery life of a ULB. Most modern aircraft, including those in the IAF inventory and commercial aeroplanes, have the device fitted on them.
In the absence of a ULB, the search teams are now looking for clues of any wreckage, oil slick of aviation turbine fuel or any other visual clue in the area. Moreover, they will be using sonar signals, which reflect off a metallic surface underwater. But undertaking these activities over an area of 4.5 lakh sq km is a time-consuming and gruelling task, which can go on for months without any success.
The missing AN-32 had two Emergency Locator Transmitters (ELTs) — one in the tail fin and the other in the cockpit. The battery life of these two devices, unlike a ULB, does not exceed 72 hours. Moreover, unlike a ULB, the ELT does not function underwater because of the ultra high frequencies signal transmitted by it.
Besides ELTs, sources said, the Soviet-made plane had four life rafts, each fitted with a Personal Locator Beacon which transmits signals on coming in contact with water.
Like the ELTs, these systems only operate on the surface of the sea and have a very limited battery life.