- Two data recorders are fitted with beacons
- Battery life is about a month
- Pings generally detected up to 2 nautical miles
Somewhere in the vast Indian Ocean, a tiny aluminum cylinder may be emitting a steady ping.
The ping itself is unremarkable, says Anish Patel, president of beacon manufacturer Dukane Seacom Inc. Patel snaps his fingers to match the pinger's rate -- one snap per second. In fact, it is inaudible to human ears.
But the whole world is listening. And the ping is taking on the cadence of a slowly failing clock.
Friday marks the 14th day of the hunt for Malaysia Airlines Flight 370, and near the halfway mark in the pinger's minimum battery life. When the battery dies, possibly around April 6, the job of finding the flight data and cockpit voice recorders will get significantly harder. And so will the job of solving the mystery of Flight 370.
A beacon of hope
Every commercial airplane is required to have pingers -- technically called underwater locator beacons -- to help locate lost aircraft. One is attached to the flight data recorder; another to the cockpit voice recorder. Find the pingers and you find the recorders. Find the recorders, experts say, and you solve the mystery of Flight 370.
But, like virtually everything in aviation, the current technology represents one step in an evolutionary path. Today's recorders are better than recorders of the past, when data was recorded on magnetic tape. But they fall short of current technical potential, with short battery lives and -- on voice recorders -- only two hours of recording capacity.
Since Flight 370 flew almost seven hours beyond the point where something went terribly wrong, it's almost guaranteed that crucial cockpit sounds have been erased.
On the positive side, the depletion of the battery will not wipe out data. Data has been known to survive years in harsh sea water conditions on modern recorders.
Cockpit voice recorders memorialize pilot's words -- from the inconsequential to the tragic. In 1999, a voice recorder captured the last words of the startled captain of EgyptAir 990 as he fought to maintain control of his plane. The cockpit voice recorder helped establish that the pilot was trying to pull the plane out of a dive while his co-pilot flew it into the ocean.
Voice recorders also record clicks and hums -- sounds that can reveal pilot's actions.
Flight data recorders capture a wide array of data, including altitudes, air speeds, headings, engine temperatures, flap and rudder positions.
"The newer aircraft typically are to record 88 or 91 parameters now, but usually we see recorders that come in for the newer aircraft of at least a few hundred parameters if not more than 1,000," a National Transportation Safety Board official said.
They must record the previous 36 hours of operations.
Enter the data into a flight simulator, and you can re-create history, using technology to solve a technological mystery.
But first you have to find the boxes.
Data recorders are built to withstand the rigors of flight and the trauma of crashes.
Recorders are required to survive short, hot blazes, such as a fuel fire, or longer but cooler blazes, such as a forest fire, were a plane to crash in the woods.
They are required to survive an impact shock of 3,400 G-forces, and have standards for static crush and fluid immersion.
They must be able to withstand hydrostatic pressures found at 20,000 feet deep. The region where searchers are now looking for Flight 370 has depths up to 13,000 feet.
The pingers are activated upon immersion in fresh or salt water, and emit a signal at 37.5 kilohertz.
To detect the signals, searchers drag hydrophones behind boats, drop them from ships or planes, or use specially equipped submersibles.
Under favorable sea conditions, the pingers can be heard 2 nautical miles away. But high seas, background noise, wreckage or silt can all make pingers harder to detect.
Changes since Air France 447
The 2009 crash of Air France 447 was a game changer in the history of underwater beacons. The battery died before searchers could locate the wreckage. It was another two years before the recorders were recovered.
Since then, regulators and the airline industry have undertaken efforts to increase the beacon battery life from 30 to 90 days. And there are efforts to require pingers to be attached to aircraft airframes, making it easier to locate wreckage. The next-generation pingers emit pings that can be heard 6 to 10 miles away, said Patel.
After 30 days
Patel believes his company manufactured the pingers on Malaysia 370.
"We are confident it could be one of ours," he said. Malaysia Airlines is a customer of Dukane Seacom, and the company's pingers have been installed on Boeing 777s.
"We're preparing to address questions should it be ours," he says.
And what is happening now with the pingers?
If it's not found soon, Malaysia 370's pingers may die with a whimper.
After 30 days, the battery will continue providing power and the beacon will ping, but the output will quickly drop, Patel says.
"As the battery 'wears down' the pinger output decreases until the battery reaches a point that no ping is emitted," Patel wrote in an e-mail to CNN. "The pings get lower and lower in 'volume' as the battery weakens."
"Our predictive models and lab tests show 33-35 days of output before we drop below the minimal value," he wrote. "Depending on the age of the battery, it could continue pinging for a few days longer with progressively lower output levels, until the unit shuts down."