What you’re looking for when you’re looking for a missing airplane

The Gulf of Thailand, seen from a search-and-rescue plane.
The Gulf of Thailand, seen from a search-and-rescue plane.
Image: Reuters/Kham
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Four days after a Malaysia Airlines 777 jet and the 239 people aboard disappeared over the Gulf of Thailand, authorities haven’t found the plane or the cause of its disappearance.

Their search has eerie parallels to the search for Air France flight 447, the last airline to disappear in flight, over the Atlantic in 2009 en route to Brazil. Then as now, two passengers were thought to be connected to Islamic extremism before authorities dismissed such speculation.

The wreckage of the Air France flight was finally discovered in 2011 by a team of oceanographers using robotic submarines that searched mountainous terrain some two-and-a-half miles (four kilometers) below the ocean’s surface. The leader of that mission, Mike Purcell, is the principal engineer at the Woods Hole Oceanographic Institution (WHOI), where he oversees the development of ocean research submersibles. He gave Quartz a sense of what searchers can expect.

The biggest difference between the two searches is that the Gulf of Thailand, with an average depth of 45 meters (148 feet), is far shallower than the mid-Atlantic region where the Air France flight went down. However, searchers for AF 447 found floating debris within a day of the flight’s disappearance, confirming that the plane had been lost. That allowed the WHOI to model currents and wind patterns in an attempt roll back the clock and determine where the debris entered the water. No such evidence has turned up yet for Malaysia Airlines 370.

Absent such debris, and assuming the plane wound up in the water, searchers will listen for “pingers” attached to the plane’s flight data recorders—the “black box”—that make a noise about once a minute after they hit water. That’s one thing Purcell thinks airlines could improve, since in the case of the Air France search, the pingers were damaged when they were discovered, and with a range of only a mile, may have been too deep to be heard.

“That’s a weakness in having to find something like this; they probably could come up with a better sound source that could be detected from much further away,” he says. “The attenuation of sound underwater is very dependent on the frequency. These beacons are relatively high frequency, if they were to use lower frequency, the range would increase significantly. But they would get a little bit bigger, weigh more, take more power, probably need more batteries.”

Another question is raised by the hunt for the black box: Why don’t flight data stream continuously from the aircraft? Even though passengers can have live internet, key information about what’s happening in the cockpit isn’t being transmitted back to the airline, a measure raised as long overdue even in 2011; today such data could have solved an even larger mystery.

The good news is that because the Gulf of Thailand is so much shallower than the mid-Atlantic ridge, a search can use sonar rigs towed behind ships, rather than advanced robots like WHOI’s Remus 6000, which operates autonomously in very deep seas.

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“I’ve looked at the charts of the Gulf of Thailand, it looks pretty flat, they’re not going to have issues like shadowing”—when undersea geography blocks sonar signals—”[but] they are going to have to deal with the fact that they are in shallow water,” Purcell says. “Sound reflecting from the surface as well as the sea floor… screws up the record, [but] the debris field is probably a strong enough signal that it can see through some of that. One thing people have to figure out right away is how far they can see out to each side as they tow their system along.”

Today, however, the Malaysian authorities expanded their search zones to include the Andaman Sea, where the ocean is as deep as 5,000 feet. That might complicate matters.

And soon, perhaps, these kinds of searches will be cheaper. Currently, a ship is need to drop the Remus 6000 in the search area and pull it out again. Purcell’s team is working to increase the submersibles’ endurance enough to send them out from shore on their investigative missions.