The next challenge would begin thousands of metres below if, as investigators hope, a black box is indeed emitting "pings" from a wreck site on the ocean floor.
"The most reasonable option from there is side-scan sonar," said Jim Gibson, general manager of Phoenix International, which is assisting the U.S. navy on the search for the missing Boeing 777 in the south Indian Ocean.
The sonar technology maps the seabed using soundwave echoes that are digitized into a computer image.
"If you have an untrained eye, you might take a look at something on that sonar trace and say, ‘How can you tell that’s manmade?’ because it looks like a black dot or a rock. But it could be the wing of an airplane," Gibson said.
Phoenix International, which also helped recover debris from Air France Flight 447 and the Space Shuttle Challenger, has several submersibles at its disposal to find the Malaysian plane, which vanished on March 9 carrying more than 200 people on a flight from Kuala Lumpur to Beijing.
"In this particular case, if — and that's a big if — they find a high probability area, they would in all likelihood use the Artemis," Gibson said.
Search zone as large as L.A.
The yellow, torpedo-shaped Bluefin 21 model of the Artemis AUV (autonomous underwater vehicles) underwent buoyancy testing last week by the Royal Australian Navy’s Ocean Shield ship.
Once deployed, the unmanned Bluefin 21 would have to search a 1,300-square-kilometre swath of ocean floor, an area equivalent to the size of Los Angeles. Covering a search zone that immense could take two months.
The sub takes pictures and has a depth rating of 6,000 metres; the possible black box sending beacons from Flight MH370 is suspected to be about 4,500 metres deep.
The purpose of the pilotless AUVs is to establish a "degree of confidence" as to the location of a debris field, Gibson explained, but the Bluefin 21 would not be able to remove objects and bring them back to the surface.
For the physical extraction phase, a remote-operated vehicle (ROV) resembling a backhoe loading cab with clampers would take the next dive.
A strong candidate to deploy would be Phoenix International’s Remora class of ROV, said Tom Dettweiler, who worked for eight years as a senior project manager for Odyssey Marine Exploration’s shipwrecks team.
The Remora was used to inspect the Titanic site in 2001 and was also used to find wreckage from Adam Air Flight 574, a domestic passenger plane that crashed into the Makassar Strait near Indonesia in 2007.
The 900-kilogram ROV is equipped with a heavy-lift system and has video capabilities.
"They have manipulators on the front, which are almost like a mechanical version of a human arm," Dettweiler said. "There are joints, a shoulder, an elbow, a wrist, and some kind of grasper on the end."
An operator can move the arm remotely, Dettweiler said. Once the operator watching a screen has the ROV positioned before the black box, he or she can close the gripper from inside the control suite.
"Slowly, so you don’t squash it," Dettweiler said. "In my experience, some of the most fragile things have been brought back like little porcelain statuettes, and they were totally intact."
Vessel can slice into fuselage
The ROV would be tethered to a larger naval ship via a fibre optic "umbilical cord" that also powers it, allowing the underwater vessel to explore the ocean depths for days at a time.
Once at the bottom, it would be able to remove, cut, slice and tear away fuselage from a wrecked plane in order to reach the pinger. The cylindrical pingers on black box recorders typically weigh seven to 10 kilograms. The vessels are able to lift items weighing more than 360 kilograms.
"It’s probably bolted down to something inside the aircraft, but these things can cut into something no problem," said Paul Tidwell, a deep-ocean salvage expert most famous for finding the sunken Second World War-era Japanese submarine I-52 in 1995.
Tidwell, who has participated in dozens of deep-water recovery explorations in the past 25 years and also advised director James Cameron on lighting techniques for 1997’s Titanic, said it could take three or four hours for the submersible to return to the surface with any objects from 4,500 metres deep.
He notes there is worry about the battery on the pinger dying.
"They do tend to overbuild these things, so hopefully it can last a little longer," he said.
Pinger may still be working
Radiant Power Corporation, which manufactured the aluminum Dukane model pinger, said the 30-day lifespan is a U.S. federal aviation authority standard.
"It’s not an exact cutoff at 30 days. It depends on the circuit current, but it may last a little longer," Parimal Patel, the test tech manager for Radiant Power, said from the firm’s headquarters in Sarasota, Fla. "It may last 32 or 33 days, maybe more."
The Ocean Shield will continue sweeping the ocean in criss-cross patterns, dragging Phoenix International’s "batwing-shaped" TPL (towed pinger locator) along with it to try to detect more pings and narrow the search zone further.
"It’s just like mowing the grass," Gibson said.
"Those chirps are very distinct bursts and they’re about one per second. The repetition of the acoustic signals is consistent and hard to mimic that from another manmade system," he said.
Investigators are picking up signals with frequency signatures of 33 kilohertz. The acoustic frequency of a pinger is 37.5 kilohertz.
Gibson reasoned some damage may have affected signal output.
As tantalizing as it would be to recover a black box and unravel the mystery over the fate of Flight MH370, Tidwell believes the passengers’ families and friends are more interested in recovering loved ones.
"One thing I do hope happens is they find [the flight data recorder], but also recover remains," Tidwell said. "For the families, they probably don’t care so much about what caused the plane to go down. More importantly, it’s to try to get some closure and return their loved ones to them. That’s the main thing."