With no new developments in the search for the missing Malaysia Airlines Boeing 777-200ER, aerial searches will be wound down and the underwater search expanded.

Australia’s prime minister Tony Abbott told reporters at a briefing in Canberra that it was “highly unlikely” that any aircraft debris would be located from further aerial searches, and those aircraft being used in the searches are “operating at close to the limit of safe and sensible operation.”

“Therefore we are moving from the current phase to a phase that is focused on searching the ocean floor over a much larger area.”

Abbott says that Canberra plans to contract commercial underwater search companies to join the search. Abbott warned, however, that it would take “some weeks to put in place these new contractual arrangements” for the enlarged search.

Those providers are expected to use towed sidescan sonar equipment to search the ocean floor for signs of possible debris, with a focus on a 700km x 80km probable impact zone.

“We will search it all,” Abbott says. “That is obviously going to take quite a few months, depending on the weather, depending on the equipment that can be deployed.”

He adds that engaging those contractors will cost around A$60 million ($56 million), and “appropriate contributions” would be sought from some of the other nations involved – most likely Malaysia and China.

The extended search would build on the missions already carried out by the Bluefin-21 autonomous underwater vehicle, which has used sidescan sonar to scan a 400km2 area of the sea floor.

That search, which focused on an area where ‘pings’ suspected to be from the aircraft’s flight data and cockpit voice recorders, has failed to find any signs of the 777.

While the underwater search continues, an Australian aircraft (likely an AP-3C Orion) would be kept on standby to offer aerial assistance, however it is expected that the majority of the foreign military aircraft involved will head back to their regular bases.

Although he stopped short of nominating a date when the aerial search will end, Abbott praised the efforts of the eight nations that have provided aircraft for the search, which has now scoured over 4.5 million square kilometres in the southern Indian Ocean.

Abbott says that the Canberra will also make approaches to the multilateral team in Kuala Lumpur and “ask them to reconsider exactly what they think is the most probable impact zone based on the data.”

The 777 was operating flight MH370 from Kuala Lumpur to Beijing during the early hours of 8 March with 239 passengers and crew on board when it went missing.

Source: Cirium Dashboard