(This story originally appeared in on Aug 02, 2016)

NEW DELHI: The Indian Air Force is now scrambling to install underwater locator beacons in its older transport aircraft, which are tasked to fly over the sea, after failing to locate the AN-32 that went down with 29 people in the Bay of Bengal on July 22.The ill-fated AN-32, which crashed in an area where the average sea depth is well over 3,000-metre, had been fitted with emergency locator transmitters (ELT) or beacons during its upgrade last September, as was earlier reported by TOI .But while an ELT can be useful in locating a plane wreckage on land, it's of little help in the sea because its emergency radio frequencies or waves cannot travel through water.Consequently, the ongoing massive hunt for the missing twin-engine AN-32, which was on way from Chennai to Port Blair, is proving extremely difficult in the absence of an underwater locator beacon to pinpoint where it could be lying on the seabed."IAF is now trying to install underwater locator beacons in the AN-32s that fly over the sea. Trials for underwater ELTs were already in progress when the crash took place. The IAF 's new-generation transport aircraft like C-130J Super Hercules and C-17 Globemaster-III have underwater ELTs," said an official.Apart from sonars of warships and submarines, officials say naval P-8I long-range maritime patrol aircraft are also now deploying sonobuoys in the ongoing search operation for the AN-32. Ejected from the P-8Is during anti-submarine warfare, the sonobuoys are designed to detect underwater objects and transmit their location back to the aircraft through radio signals.The search so far has centred around "a probable crash zone" based on the last radar contact with the AN-32, which went into a steep downward spiral from a 23,000-feet altitude about 151 nautical miles due east of Chennai at 9.12am on July 22.As earlier reported by TOI, the AN-32 had been upgraded with airframe strengthening and newer avionics but had suffered three technical snags in early-July. It had two ELTs — a stationary US-made ARTEX C406-1 in the tail fin and a French-made portable KANNAD 406AS kept in the cockpit.While the former is automatically activated by an impact with a certain amount of G-force (over 2.3 G) equivalent to a crash, the latter has to be manually activated by the pilot. There are also four life rafts fitted with personal locator beacons (PLBs), which get activated after coming in touch with seawater, on board the AN-32s.The AN-32 that crashed was among the 50 such twin-turboprop aircraft upgraded till now to increase their operational life from the earlier 25 years to 40 as well as newer avionics under the $ 398 million (Rs 1,965 crore) contract inked with Ukraine in June 2009.Of the 101 AN-32s in the IAF fleet, inducted from the erstwhile Soviet Union from 1984 to 1991, the first 40 aircraft were "re-equipped" in Ukraine, while the rest 61 are progressively undergoing the same at the 1 Base Repair Depot at Kanpur.