Although official confirmation hasn’t been made, the exhaustive and, if necessary, long-term deep-sea search for the wreckage of missing Malaysia Airlines flight MH370 is due to get underway in the southern Indian Ocean south-west of Perth today.

The first of the deep-sea search ships, GO Phoenix, was due on station yesterday, but its instrumented “towfish” and its 10,000 metres of cabling take time to deploy and manage. The device has to be raised and lowered with high precision to maintain optimum position above the only recently mapped ridges, gorges and other obstacles of a complex sea floor that exceeds a depth of 6000 metres in places.

But there is no doubt anymore that somewhere in the southern Indian Ocean, maybe 1800 kilometres from Perth, maybe as far out as 2700 kilometres, lies the wreckage of missing Malaysia Airlines flight MH370, which was carrying 239 passengers and crew. The plane crashed into the ocean after inexplicably diverting from its intended flight path between Kuala Lumpur and Beijing only 40 minutes into a flight that was due to last almost six hours.

Analysis of satellite relayed signals from a data reporting system on the Boeing 777-200ER and an unsuccessful call to a Malaysia Airlines satellite phone, which was on standby mode in the cockpit, confirm that the flight eventually flew south for hours into the empty skies over the southern Indian Ocean before its fuel ran out.

The latest analysis suggests a tight, high-speed spiral preceded an impact with the ocean surface some seven hours and 39 minutes after takeoff.

However, estimating the exact impact point is beset  with uncertainty because that Search Strategy unit, which is funded by, and reports to, Malaysia and advises the Australian-managed search effort, doesn’t know exactly what speed and altitude settings were flown by MH370 on its final long southerly path, nor even the precise point, somewhere north of Sumatra, where it changed course.

GO Phoenix is trawling a submarine world where no sunlight falls, where there is no day or night,  and whose features were unknown in any detail until they were mapped by bathymetric survey to prepare the way for a methodical and high-resolution search, supported by instruments that can detect even traces of jet fuel in those depths.

Down in this cold, high-pressure and timeless vast darkness is the hard wreckage of the engines, cabins, cockpit, undercarriage and “black box” data and sound recording devices, and possibly some remains of those on board.

After the wreckage of Air France flight AF447 was found in the mid-Atlantic in 2011, 22 months after it crashed, killing all 228 people on board, the data recorders, critical parts of its structure, and 104 bodies were retrieved from an abyssal plain at a depth of 3980 metres.

Finding MH370 could take a day, or a year or more — that is, provided it hasn’t been buried under a landslide, dislodged by striking a cliff face, or covered up by the effects of a sea-quake.

The disappearance of MH370 is the most baffling mystery in the history of flight.