Kuala Lumpur:
The lead coordinator of the search for Malaysia Airlines Flight 370 said Monday that after six days without detecting any further underwater signals that could be from the plane's flight recorders, searchers planned to take the hunt to the dark depths of the Indian Ocean, deploying a submersible vehicle to scan the seabed for any signs of wreckage.
The absence of any more pings, taken together with the belief that the batteries on the flight recorders were at the end of their life span, has led authorities to conclude that they are unlikely to detect any further signals and that they need to shift search tactics.
"It is time to go underwater," the lead coordinator, Angus Houston, said at a news conference in Perth, Australia.
But striking a note of caution that has become a motif of his public appearances, Houston said there was no guarantee that searchers would find the wreck.
"Don't be overoptimistic," he said. "Be realistic."
He added, "It may be very difficult to find something, and you don't know how good any lead is until you get your eyes on the wreckage."
The decision to deploy the submersible opens a new phase in the search for the flight recorders and the rest of the plane's wreckage, which might provide crucial evidence in determining what caused the Boeing 777-200 to veer off its scheduled route from Kuala Lumpur to Beijing on March 8 and vanish with 239 people on board.
Houston said the submarine's deployment would happen as soon as Monday evening.
Search coordinators had hoped to capture more signals in order to better locate the sources.
"Despite the lack of further detections, the four signals previously acquired, taken together, constitute the most promising lead we have in the search," Houston said. "We need to pursue this lead as far as possible."
He did not specify the size of the prospective search zone on the seabed, only calling it "a reduced and manageable search area."
Houston also said that an oil slick had been detected in the search zone and that samples had been recovered for testing but that results would not be available for several days. The slick was about three and a half miles away from the area where searchers had detected the underwater signals.
For their underwater hunt, search officials had been depending on the so-called towed pinger locator, essentially an elaborate microphone that a crew has dropped about a mile below the surface and dragged behind the Ocean Shield, an Australian naval vessel. The locator detected two sets of signals on April 5 and two more on April 8 in an area about 1,000 miles northwest of Perth.
With the move to the ocean floor, the searchers' most valuable tool will become a Bluefin-21, a remote-controlled submersible operated by a U.S. team that has also been in charge of the pinger locator. The submarine will initially take sonar scans of the seabed.
But moving around walking speed, it has the ability to cover only about 12 square miles a day. Some experts say the four signal detections have left searchers with a total search zone of possibly hundreds of square miles.
If technicians on board Ocean Shield see anything in the scans that warrants closer attention, they will outfit the Bluefin with a camera and send it back down to take photographs.
The ocean floor in the area of the pings is about 2.8 miles deep, putting the search at the limit of the Bluefin's diving range.
In the meantime, Houston said, planes and vessels would continue to scour the ocean surface in hopes of finding debris from the plane. Despite weeks of searching, no debris from the aircraft has been recovered.
Search officials said in a news release that as many as 12 aircraft and 15 ships would be deployed in the search Monday across an area of about 18,000 square miles. The center of the search zone lies about 1,400 miles northwest of Perth and several hundred miles west of the area where Ocean Shield has been trawling for pings. Investigators believe that any plane debris is likely to have drifted far from the point where the plane entered the ocean.
Though encouraged by the four signals gathered over the past week and a half, search officials have cautioned that a successful identification of the plane could take a long time, with some exploration experts predicting that a search and recovery effort of this sort could take more than a year.
Among the challenges that searchers face in the hunt for Flight 370 is the unfamiliarity of the seabed of the Indian Ocean west of Australia, which has not been fully mapped. Houston said the seabed was thought to resemble rolling hills but was covered in deep layers of silt, which could impede discovery and recovery of wreckage.
Moreover, the extreme depths in the area will limit the set of exploration tools at the searchers' disposal.
"I think this is an area that is new to man," Houston said Monday, calling the environment "very demanding."
The Bluefin-21, made by Bluefin Robotics of Quincy, Mass., and owned by Phoenix International Holdings, a Navy contractor in Largo, Md., is a torpedo-shaped vehicle about 17 feet long that will cruise some 300 to 400 feet above the seabed. Using a sonar system, it will create a high-resolution, 3-D map of the bottom that technicians on board the Ocean Shield will evaluate for signs of wreckage.
Houston explained that each deployment of the Bluefin would last a minimum of 20 hours: two hours for the Bluefin to descend, 16 hours to conduct its scans and two hours to return to the surface. Technicians will then take about four hours to download and analyze the data before deploying the submarine on another dive. The team will have no indication of what the vehicle is seeing until it returns and the data is downloaded.
Houston said that in its first mission, the Bluefin would cover an area of about 15 square miles.
The vehicle "has the potential to take us a further step towards visual identification, since it offers a possible opportunity to detect debris from the aircraft on the ocean floor," he said.
If the water turns out to be deeper than the Bluefin can handle, he said, officials will have to employ another submersible with the ability to dive to greater depths.
If the search crew sees something intriguing in the sonar scans, they will fit the Bluefin with a camera and send it on a course about 20 feet from the sea bottom, taking photos.
The final phase of the investigation would involve the recovery of the black boxes and possibly elements of the wreckage along with corpses to help investigators determine what happened to the plane. The circumstances of its disappearance, currently the focus of a criminal investigation by the Malaysian authorities in collaboration with international investigators, could demand a careful examination of any debris discovered on the seabed.
But officials warned that the search effort was possibly still a long way from that stage.
"I would caution you against raising hopes that the deployment of the autonomous underwater vehicle will result in detection of the aircraft wreckage," he said. "It may not. However, this is the best lead we have, and it must be pursued vigorously. Again, I emphasize that this will be a slow and painstaking process. We have got to find wreckage visually before we can finally say we have solved this mystery."
Houston also clarified that analysts had discounted other underwater signals that a Chinese vessel, Haixun 01, reported hearing on April 4 and 5.
The four sets of transmissions detected by Ocean Shield as well as the oil slick discovered in the same vicinity are "all we have really got," he said. "We have no visual objects. That is where we are."
© 2014, The New York Times News Service