Teams searching for a missing Malaysian airliner were planning to send an unmanned submarine into the depths of the Indian Ocean to look for wreckage, an Australian official leading the multination search said Monday.
The deployment of the submersible drone opens a new phase in the five-week search, one focusing on a pitch-black, silt-covered patch of the ocean floor. The drone moves at walking speed, and searching with it will be painstaking. But it allows investigators to follow up on their best lead to date: deep-sea acoustic signals that are believed to have come from the Boeing 777's black box.
The submersible drone, known as the Bluefin-21, will use sonar to provide search crews with a three-dimensional map of the Indian Ocean floor, an area so unexplored that it is practically "new to man," said Angus Houston, the Australian official in charge of the search. The Bluefin-21 was expected to begin its mission Monday evening.
Thirty-eight days into the search for Malaysia Airlines Flight 370, which vanished with 239 passengers and crew on board, there have been no confirmed sightings of debris.
The best hint of the plane's location comes from four acoustic signals -- potential black-box transmissions -- detected by an Australian naval vessel equipped with specialized listening equipment. But the last transmission came six days ago, and the aircraft black-box batteries are already well past their 30-day shelf life. The batteries by now may have died, Mr. Houston said.
"I would caution against raising hopes that the deployment of the autonomous underwater vehicle will result in the detection of aircraft wreckage," Mr. Houston said. "It may not. However, this is the best lead we have. We've got to find wreckage before we can finally say we've solved this mystery."
The Bluefin-21 -- 16 feet long, yellow, shaped like a submarine -- was already on board the Australian vessel, the Ocean Shield, operating roughly 1,050 miles northwest of Perth. For more than a week, the Ocean Shield has been dragging a towed pinger locator through the water to listen for possible pings from Flight 370's black box.
Mr. Houston also said Monday that the Ocean Shield came across an oil slick about 31/2 miles downwind from the area where it picked up the signals. Though the oil slick could be unrelated to the plane, about half a gallon has been sampled for analysis -- a process that will take several days, Mr. Houston said.
The Ocean Shield doesn't have the capability to use the towed pinger locator -- tied to miles of cables -- and the Bluefin-21 at the same time. The four pings were detected in a loose oval about 20 to 25 miles apart; that translates into an underwater search zone of some 500 square miles. Search officials had been hoping that additional detections could help narrow the ocean floor area where the submersible will scan for evidence of the plane. The U.S. Navy said the submersible will need anywhere from six weeks to two months to scan the underwater search area.
Australian Prime Minister Tony Abbott last week said authorities were "confident" the deep-sea pings were coming from the missing jet's flight data and cockpit voice recorders.
The underwater operation will be a slow one, moving in 24-hour cycles. The submersible will spend 20 hours at a time underwater: two hours to make the dive, 16 hours scanning the depths, and two more hours for the ascent. Ocean Shield crew members will then take four hours to download the data. The Bluefin-21 does not transmit information about what it is seeing in real time.
The Bluefin-21 will be operating in depths approaching its technological limits, but U.S. naval officials say they believe that the drone will be effective.
Mr. Houston said the submersible would begin its search "in the most likely spot" of the wreckage, but he gave no additional specifics about that location. He added that a search for any debris bobbing on the ocean surface could wind down later this week after consultation with the other countries involved. "The chances of any floating material being recovered have greatly diminished," he said.
For now, the disappearance of Flight 370 -- a red-eye from Kuala Lumpur bound for Beijing -- remains a dismaying mystery. Malaysian authorities say the flight was steered off course deliberately, though they have not indicated a culprit or provided any suggestion of a motive.