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Herculean task to find more “pings”: MH370

Angus Houston, the retired Australian air chief marshal who is heading
the search far off Australia's west coast, said sound locating equipment
on board the Ocean Shield has picked up no trace of the signals since
they were first heard late Saturday and early Sunday.

Time may have already run out to find the devices, whose locator beacons
have a battery life of about a month. Tuesday marks one month since the
plane vanished. Once the beacons blink off, locating the black boxes in
such deep water would be an immensely difficult, if not impossible,
task.

"There have been no further contacts with any transmission and we
need to continue [searching] for several days right up to the point at
which there's absolutely no doubt that the batteries will have expired,"
Houston said.

If, by that point, the U.S. navy listening equipment being
towed behind the Ocean Shield has failed to pick up any signals, a sub
on board the ship will be deployed to try and chart out any debris on
the sea floor. If the sub maps out a debris field, the crew will replace
the sonar system with a camera unit to photograph any wreckage.

Houston's comments contradicted an earlier statement from Australia's
acting prime minister, Warren Truss, who said search crews would launch
the Bluefin 21 autonomous sub on Tuesday.

The towed pinger locator detected late Saturday and early Sunday two
distinct, long-lasting sounds underwater that are consistent with the
pings from an aircraft's "black boxes" — the flight data and cockpit
voice recorders, Houston said, dubbing the find a promising lead in the
month-long hunt for clues to the plane's fate.

Still, officials warned it could take days to determine whether the
sounds were connected to Flight MH370, which vanished March 8 on a
flight from Kuala Lumpur, Malaysia, to Beijing with 239 on board.

"This is an herculean task — it's over a very, very wide area, the
water is extremely deep," Defence Minister David Johnston said. "We have
at least several days of intense action ahead of us."

Houston said finding the sound again was critical to narrowing down
the search area before the sub can be used. If the vehicle went down now
with the sparse data collected so far, it would take "many, many days"
for it to cover all the places the pings might have come from.

"It's literally crawling at the bottom of the ocean so it's going to take a long, long time," Houston said.

Despite the excitement surrounding the Ocean Shield's
sound detections, Houston warned that the search had previously been
marred by false leads — such as ships detecting their own signals.
Because of that, other ships cannot be sent in to help with the
underwater search, as they may add unwanted noise.

"We're very hopeful we will find further evidence that will confirm
the aircraft is in that location," Houston said. "There's still a little
bit of doubt there, but I'm a lot more optimistic than I was one week
ago."

Finding the black boxes is key to unravelling what happened to the
Boeing 777, because they contain flight data and cockpit voice
recordings that could explain why the plane veered so far off-course.

"Everyone's anxious about the life of the batteries on the black box
flight recorders," said Truss, who is acting prime minister while Tony
Abbott is overseas. "Sometimes they go on for many, many weeks longer
than they're mandated to operate for — we hope that'll be the case in
this instance. But clearly there is an aura of urgency about the
investigation."

The first sound picked up by the equipment on board the Ocean Shield
lasted two hours and 20 minutes before it was lost, Houston said. The
ship then turned around and picked up a signal again — this time
recording two distinct "pinger returns" that lasted 13 minutes. That
would be consistent with transmissions from both the flight data
recorder and the cockpit voice recorder.

The black boxes normally emit a frequency of 37.5 kilohertz, and the
signals picked up by the Ocean Shield were both 33.3 kilohertz, U.S.
Navy Capt. Mark Matthews said. But the manufacturer indicated the
frequency of black boxes can drift in older equipment.

Houston said the frequency of the sounds heard was considered "quite
credible" by the manufacturer, and noted that the frequency from the Air
France jet that crashed several years ago was 34 kilohertz. Pressure
from being so deep below the surface and the age of the batteries can
also affect the transmission level, he said.

The frequency used by aircraft flight recorders was chosen because no
other devices use it, and because nothing in the natural world mimics
it, said William Waldock, a search-and-rescue expert who teaches
accident investigation at Embry-Riddle Aeronautical University in
Prescott, Ariz.

But these signals are being detected by computer sweeps, and "not so
much a guy with headphones on listening to pings," said U.S. navy
spokesman Chris Johnson. So until the signals are fully analyzed, it's
too early to say what they are, he said.

"We'll hear lots of signals at different frequencies," he said.
"Marine mammals, our own ship systems, scientific equipment, fishing
equipment, things like that. And then of course there are lots of ships
operating in the area that are all radiating certain signals into the
ocean."

The Ocean Shield is dragging a ping locator at a depth of
three kilometres. It is designed to detect signals at a range of 1.8
kilometres, meaning it would need to be almost on top of the recorders
to detect them if they were on the ocean floor, which is about 4.5
kilometres deep.

Meanwhile, the search for any trace of the plane on the ocean's
surface continued Tuesday. Up to 14 planes and as many ships were
focusing on a single search area covering 77,580 square kilometres of
ocean, 2,270 kilometres northwest of the Australian west coast city of
Perth, with good weather predicted, said the Joint Agency
Co-ordination Centre, which is overseeing the operation.