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Emergency Beacons Not Fool-Proof When Jets Go Missing

<p>Experts say it's not surprising that no emergency signals have been picked up -- especially if the plane is underwater.</p>

As the hunt for the missing Malaysia Airlines jet continues, experts say it's not surprising that no emergency signals have been picked up — especially if the plane is underwater.

When a commercial plane crashes, an emergency locator transmitter (ELT) is designed to switch on automatically to send a signal to help searchers find the crash site. But they don't always work, and it is not clear that the missing jet did crash.

"ELTs in general are extremely reliable, but it's not surprising — there's always a chance the system didn't work for some reason," said aviation safety expert Todd Curtis, the founder of That reason could include a major crash.

In fact, a 2009 report from the Airplane Owners and Pilots Association said even newer ELTs successfully activate only about 82 percent of the time. The original generation of ELTs, which came out in 1973, had an activation rate of 25 percent, but that has improved over the decades.

Boeing declined to comment on the type of ELT with which the missing Malaysia Airlines Boeing 777-2H6 was outfitted. Curtis — who worked as an airline safety engineer at Boeing for more than eight years — pointed out that the airline could have updated the craft's ELT anyway.

ELT signals are meant to continue broadcasting for 30 days, Curtis said, and they may be picked up by a variety of technology including satellites and aircraft searching overhead.

But that's only if the plane and ELT are on land. If the plane is underwater, that poses a new set of problems.

"If the airplane had crashed on land and survived the impact, then there’s a probability that the actual ELT would still be working," former National Transportation Safety Board investigator Greg Feith said on TODAY on Saturday. "But when it goes into the water, it’s a whole different story."

Read More: Race Against Time in Search for Malaysia Airlines Flight 370

In that case, the plane's so-called black box has an Underwater Locator Beacon that "pings" out sound when submerged. But that would require searchers to be close enough to pick up the sound.

"You won’t get that signal above water, over the top of the water, using an airplane trying to find a signal,” Feith told TODAY.

David Gallo, the director of special projects at Woods Hole Oceanographic Institution, said he has “very little faith in pingers." Gallo served as the co-leader of the search for Air France 447, which plunged into the mid-Atlantic in 2009.

The main problem with relying on pingers, he said, is that “the ocean can play a lot of tricks with sound."

NBC News' Alan Boyle and Matthew DeLuca contributed to this report.