By Byron Kaye and Matt Siegel
SYDNEY/PERTH, Australia, April 20 (Reuters) - The search for missing Malaysia Airlines Flight MH370 entered its 44th day on Sunday as Australian search officials said a crucial series of sonar scans of the Indian Ocean floor could be completed within a week.
The air, surface and underwater search is now focused on footage taken by a U.S. Navy deep sea drone, which has narrowed its target range to a tight 10-km (6.2-mile) circle of sea floor.
The Bluefin-21 autonomous underwater vehicle (AUV) has spent the past week scouring the remote and largely unmapped stretch of ocean floor some 2,000 km (1,200 miles) northwest of the Australian city of Perth for signs of the plane, which disappeared on March 8 with 239 people on board.
The remote controlled submarine is now in its eighth deep sea mission with no sign of wreckage so far. The drone has searched about half its targeted area, the authorities said on Sunday.
The Malaysian government has said the search is at a "very critical juncture" and asked for prayers for its success. Malaysian Acting Transport Minister Hishammuddin Hussein has also said the government may consider using more AUVs in the search.
After almost two months without a sign of wreckage, the current underwater search is centred on an area where one of four acoustic signals believed to be from the plane's black box recorders was detected on April 8.
Weeks of daily sorties have failed to turn up any trace of the plane, even after narrowing the search to an arc in the southern Indian Ocean, making this the most expensive such operation in aviation history.
Hopes for further black box signals are fast diminishing, since the black box batteries are now two weeks past their 30-day expected life span, search officials have said.
But while the Bluefin-21's target range has narrowed, the air and surface search continues unabated, with daily sorties a week after Australian search coordinator retired Air Chief Marshal Angus Houston said the air and surface component of the search would end within three days.
On Sunday, up to 11 military aircraft and 12 ships will help with the search, covering a total of roughly 48,507 square km (18,729 sq miles) across two areas, the Perth-based Joint Agency Coordination Centre said in a statement. (Editing by Clarence Fernandez)
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