"There is no doubt about it; you will be pushing the limits of the technology. It is not a straightforward operation," Wells, who believes that the black box could be more than 14,000 feet below the surface, said.
Such depths are well below the reach of manned craft and the oil industry has significant unmanned deep-sea capability, but only operates down to 9000 feet.
However, a handful of deep-sea prowlers such as the US Navy's Alvin, which surveyed the wreck of the Titanic at 12,000 feet below the Atlantic in 1986, could be equipped for such depths.
Till now, the deepest hunt undertaken for an airliner is for South African Airways Flight 295 which crashed into the Indian Ocean near Mauritius in 1987, with investigators recovering the cockpit voice recorder after a three-month search from a record depth of more than 14,000 feet.
Besides a US Navy report based on similar disasters, released under the Freedom of Information Act late last year, found it was possible to recover aircraft wreckage including the black boxes from depths of up to 18,000 feet, citing advances since the 1980s in technology such as sonar for combing rugged sea floors, new software and accoustic beacons or "pingers" which indicate a position under water.
Meanwhile, Arslanian is optimistic that even if the black boxes are not found, it will not hamper their investigations, as there are "other ways" of recovering information.
The agency's director said, for instance, initial investigations have confirmed that the plane faced no problem "before its departure from Rio."
"This catastrophe - which is the worst that our country has witnessed in terms of aviation, took place in a very difficult region...so the investigation will not be easy...but we are not giving up."
It is "essential we check and verify everything," Arslanian said.
"Without them (black boxes) it will be very difficult to reach established fact, but we can reach a possible explanation," he added.
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