By Andy Pasztor and Rachel Pannett
An unmanned submersible began scanning the seabed for signs of
Malaysia Airlines Flight 370, marking a new phase in the search in
which authorities are facing a protracted and complex mission.
The primary goal remains recovering the Boeing 777's flight-data
and cockpit-voice recorders. But with no signals resembling those
devices detected in the past six days, it was increasingly likely
the batteries powering the emergency locators were dead, prompting
search crews to turn to the U.S. Navy's underwater Bluefin-21
vehicle, which uses sonar to scan the ocean floor.
"I would caution you against raising hopes that the deployment
of the autonomous underwater vehicle will result in the detection
of the aircraft wreckage--it may not," said Australian Air Chief
Marshal Angus Houston, who is leading the multinational search.
"However, this is the best lead we have and it must be pursued
vigorously."
The boundaries of the Bluefin-21's search zone encompass roughly
500 square miles. The device moves at a walking pace, and scanning
the entire search area was expected to take between six weeks and
two months.
Even if the Bluefin identifies the "black box" recorders or
other remnants, difficult decisions would need to be made about
when to begin photographing wreckage and which portions to try to
recover for further analysis--choices complicated by the ocean's
roughly 3-mile depth.
After completing about six hours of its first mission Monday,
the submersible reached its operating depth limit of 2.8 miles, and
its built-in safety feature returned it to the surface. The data
were being analyzed early Tuesday, and authorities planned to
redeploy the vehicle again later in the day.
The Bluefin can be programmed to conduct a specific search
mission of about 20 hours, using side-scan sonar to pick out unique
features on the ocean floor. If the data show an anomaly, the
Bluefin would have its sonar equipment replaced with a high-grade
underwater camera.
Mapping the location of any parts on the ocean floor is a
crucial preliminary step to sending cameras down to document the
scene. But searchers don't want to take photographs too early,
before they have a good sense of what's there. The challenges of
getting the timing right, said Claude Lelaie, a former senior
safety official at European plane maker Airbus Group NV, "are a lot
more complicated than people are suggesting, and it could easily
take several years" to retrieve everything investigators would like
to study.
Verification of any wreckage by the Bluefin would be a long way
from snaring and bringing pieces to the surface, said John Purvis,
a former head of accident investigations for Boeing. Salvage
operations require different technologies with a dramatically
different mission, Mr. Purvis said. "The hard part is really just
starting."
Previous searches, according to Mr. Purvis and other air-safety
experts, underscore the importance of finding and analyzing debris
at or near the surface of the water as a way to obtain important
clues about how the aircraft went down.
For example, information about the likely angle of the jet's
nose as it entered the water could help searchers determine the
location and size of the pieces they are likely to find on the
bottom.
That is one reason why the multinational air and marine search
for debris has continued across a much larger area despite several
false leads on debris that turned out to be garbage.
"It's important to avoid prematurely shutting down the aerial
reconnaissance," said Nick Stoss, retired head of aircraft
investigations for the Transportation Safety Board of Canada.
The Malaysian plane veered sharply off course March 8, en route
to Beijing from Kuala Lumpur, with 239 passengers and crew. The
deployment of the Bluefin on Monday marked 38th day with no hard
evidence of precisely where the jet ended up.
Authorities believe the plane crashed into the Indian Ocean far
off the western coast of Australia after running out of fuel.
In the Indian Ocean, "currents can be wicked even at these
depths," said Mr. Purvis, making it imperative to get an accurate
sonar depiction of wreckage before any retrieval operations begin.
Once teams start trying to bring up pieces from depths greater than
1,000 feet, it quickly "moves from being expensive to being
horrendously expensive," Mr. Purvis said.
Further complicating the search is uncertainly about conditions
on the seabed. Authorities expect to encounter a blanket of silt,
which may be covering part or all of any plane debris.
"Each of these operations is going to be different, but if you
take a look at Air France 447, [the black box] was just a couple of
miles away and it took two years to find," said U.S. Navy Capt.
Mark Matthews, who is coordinating the underwater search from
Perth.
"We've got more uncertainty in this case, and if we found it on
Day One I'd be shocked."
Subscribe to WSJ: http://online.wsj.com?mod=djnwires