The hunt for Flight MH370 has failed to turn up any debris, but its unprecedented scale in one of the world's remotest locations has provided valuable lessons for future search and rescue missions.
The Malaysia Airlines plane disappeared en route from Kuala Lumpur to Beijing on March 8, 2014, with mourning families and friends of the 239 people on board still waiting to hear what happened 12 months later.
There has been no trace of the Boeing airliner despite an extensive air and sea search.
Four ships, coordinated by Australia, continue to scour a huge underwater area at least 1,600 kilometres (1,000 miles) from the nearest piece of land in a stretch of the Indian Ocean previously only mapped by satellite.
"The size of the area we're covering is unprecedented," search chief Martin Dolan, head of the Australian Transport Safety Bureau, told AFP.
"At most, when the French were looking for Air France 447, it covered a quarter of the sort of area we have in mind."
Flight AF447 was hauled from the Atlantic nearly two years after it crashed in 2009 en route from Rio de Janeiro to Paris.
The MH370 search -- jointly funded by Australia and Malaysia with a budget of Aus$120 million (USD 93 million) -- is focused on a 60,000 square kilometre (23,000 square mile) priority area and is scheduled to end in May.
The thin, long stretch of water is within the so-called seventh arc, where the plane was calculated to have emitted a final satellite "handshake".
After months of painstaking efforts, which have seen the ocean floor in the area mapped for the first time, all authorities have found is a handful of shipping containers.
The search area is so remote that the four vessels involved -- Fugro Supporter, Fugro Equator, Fugro Discovery and GO Phoenix -- need up to six days to reach it from the Australian port of Fremantle, where they routinely refuel and restock.
While at sea, they frequently encounter conditions similar to the "Roaring Forties" north of Antarctica, winds that whip up mountainous seas.
The turbulence penetrates below the ocean surface, buffering the 10-kilometre (six-mile) long tow cables extending into the water with sophisticated sonar systems attached.
The systems scour the never-before studied ocean floor in pitch-black conditions, with the plane believed to have sunk to depths of 4,000 metres (13,100 feet).
"Sunlight doesn't get more than about 300 or 400 metres into the sea and we're talking about 4,000 metres depth... literally working in the dark," Dolan said.
