Australian officials say Malaysia Airlines Flight MH370 was most likely on autopilot when it crashed into the Indian Ocean, further south than previously thought.
The new analysis comes more than 100 days after the Boeing 777, carrying 239 passengers and crew, disappeared on 8 March shortly after taking off from Kuala Lumpur bound for Beijing.
Investigators say what little evidence they have to work with suggests the plane was deliberately diverted thousands of kilometres from its scheduled route before eventually plunging into the Indian Ocean.
The search was narrowed in April after a series of acoustic pings thought to be from the plane's black box recorders were heard along a final arc where analysis of satellite data put its last location, Reuters reports.
But a month later, officials conceded that the wreckage was not in that concentrated area, some 1600 km off the northwest coast of Australia, and the search area would have to be expanded.
Australia's Deputy Prime Minister Warren Truss said on Thursday it is "highly likely" that the plane was on autopilot - otherwise it could not have followed the orderly path that has been identified through satellite sightings.
Mr Truss said the new search area was determined after a review of satellite data, early radar information and aircraft performance limits after the plane diverted across the Malaysian peninsula and headed south into one of the remotest areas of the planet.
The next phase of the search is expected to start in August and take a year, covering some 60,000sq km at a cost of US$56 million or more. The search is already the most expensive in aviation history.
The new priority search area is around 2000km west of Perth, a stretch of isolated ocean frequently lashed by storm force winds and massive swells.