Why didn’t the emergency beacon for Flight 370 work?

NEW YORK (CNN) – Malaysia Airlines Flight 370 has been missing for more than a month and a half. While the hunt for the aircraft initially focused on tracing the pings from black boxes in the Indian Ocean, there’s another type of locator signal that’s supposed to be activated in most crashes. This time, it stayed silent.

It’s one of the most baffling questions in an already-confounding mystery: why didn’t any emergency beacons on the missing plane send a distress signal?

They’re called ‘emergency locator transmitters’, ELT’s, and a senior Malaysian Aviation source tells CNN there were four of them on the plane.

“The emergency locator transmitter is a small radio transmitter that sends a signal that’s detected by satellites in the event of an airplane crash,” said aviation analyst Jeff Wise.

Signals sent by ELT’s to satellites are then relayed to monitoring stations on the ground. The ELT’s are not related to the pinger, the signal coming from the black boxes containing the flight recorders.

These beacons are designed to be activated if they sense extreme deceleration, or by impact. Those are circumstances which could have played out with Flight 370. Experts say there are other possible scenarios with the missing plane, where the ELT’s would not have worked.

“If the plane crashes with too much velocity into the surface so that the entire plane is disintegrated. Also if the plane lands gently enough, for instance in the case of Captain Sullenberger in the miracle on the Hudson– the plane set down gently enough that there wasn’t sufficient g-force to activate the ELT’s,” said Wise.

Other reasons why those beacons wouldn’t have worked: a crash could have broken the ELT antennas. Also, there’s a time lag after impact, it takes 50-seconds for the first signal to be transmitted.

“Even after it hits the water, it has to stay afloat for more than 50-seconds, or they won’t sound either.”

So even two ELT’s placed near the plane’s life-rafts and triggered by contact with salt water might be useless. That’s because ELT’s don’t work underwater.

“Once these things become submerged, the radio signal is no longer able to reach the satellite,” said Wise.

Could the emergency locator transmitters aboard Malaysia Airlines Flight 370 have been tampered with?

Experts say two of them, attached to the fuselage, would probably have been inaccessible to anyone on board. The two transmitters near the life-rafts, which are portable, could have been tampered with.

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