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Joseph Kolly, director of research and engineering for the National Transportation Safety Board, describes how flight data and voice recorders offer clues about what leads to a plane crash. / Bart Jansen, USA TODAY

WASHINGTON - Recorders like those aboard missing Malaysia Airlines Flight 370 store crucial information about why a plane crashed, from the pilot's final words to hundreds of pieces of data about how the plane was behaving.

Intense, long-lasting fires occasionally destroy the data and voice recorders, but investigators at the National Transportation Safety Board routinely recover information from recorders found months or years after ocean crashes. The machines, which are carried aboard every airliner, are certified to survive up to 20,000 feet underwater.

"We've been able to get the data out of not just flight data recorders, but any kind of electronics that have gone through incredible amounts of impact damage or saltwater submersion," Joseph Kolly, director of the NTSB's office of research and engineering, said Friday. "The successes are what keep you optimistic."

Authorities from 26 countries have searched for Malaysia's Boeing 777-200ER since it went missing March 8 with 239 people aboard. Based on satellite tracking, the search is focused on the southern Indian Ocean, where satellites have photographed debris, but foul weather has prevented any confirmation of the jet.

If the jet's debris is found, searchers will track ocean currents in an effort to find the wreckage ?? and the recorders ?? on the ocean floor. In the case of Air France Flight 447, which crashed in the Atlantic in 2009, the recorders were found with usable data nearly two years later.

Other cases where recorders were retrieved from the ocean include TWA Flight 800 in 1996, EgyptAir Flight 990 in 1999 and Alaska Airlines Flight 261 in 2000.

"We would continue to always look for these recorders assuming that we can get the data," Kolly said.

Malaysia remains in charge of the search but could defer once the wreckage is found to the NTSB to determine what went wrong. The NTSB, which recently spent $2 million upgrading its lab, is one of a handful of sophisticated labs worldwide that could dry out the recorders and decipher their information, Kolly said.

The NTSB retrieves information from 150 flight recorders per year, about half voice and half data, and from about 650 devices per year including cellphones, iPads and GPS units, Kolly said. One-third of the cases are from overseas, where other governments ask for assistance in their investigations, he said.

"There are only a few labs that have this kind of capability," Kolly said.

To help find them, the recorders have "pingers" certified to broadcast a signal for at least 30 days after coming into contact with water. A federal regulation calls for pingers to last for 90 days starting in 2015. The Malaysia flight's pinger should last at least 10 more days and perhaps a few weeks longer, depending on water temperature and other factors.

At 35 kilohertz, the pings are not audible to the human ear. Sonar can hear them up to 2 miles away underwater and at shorter distances depending on topography and whether wreckage is muffling them. In the lab, a converter renders the sound like the chirp of a ticking grandfather clock.

If recorders are disconnected from power on the plane, they stop functioning. A pilot could pull a circuit breaker to stop them, as investigators suspect happened in the SilkAir Flight 185 crash in 1997. Or a fire could knock them out, as happened five minutes before Swissair Flight 111 crashed off the coast of Nova Scotia in 1998.

Investigators are always looking for clues from the recorders. The voice recorder keeps two hours, up from 30 minutes after an NTSB recommendation in 1999. The data recorder keeps 25 hours of information.

If the NTSB deals with recorders retrieved from the ocean, the first step is to keep them submerged in fresh water. This prevents possible corrosion from saltwater or engine fuel.

The recorders are then flown to the NTSB's Washington headquarters aboard a Federal Aviation Administration plane. The water-filled container sometimes attracts attention like emergency workers carrying an organ for transplant.

"You get some funny looks walking through the airport sometimes," said Erin Gormley, an aerospace engineer at the NTSB.

The metal containers for recorders, nicknamed "black boxes," are actually orange and cylindrical with the words "Flight Recorder Do Not Open" on the outside.

At the NTSB's lab, engineers wearing rubber gloves and anti-static wristbands carefully unscrew the containers to pry open insulation for a computer board with chips that store the plane's memory.

The recorders are dried slowly and deliberately in a vacuum oven. Investigators are eager to get information quickly, in the first day, to relay tips to colleagues at the wreckage site for where to look.

When the plane's information gets to the chips, it is stored in different areas, so a single damaged chip doesn't cost the investigation all the information about speed or about the final hour of flight.

"We have a good success rate with recovery," Gormley said. "The data does jump from chip to chip. We should still be able to build the information back."

The data are downloaded in a binary of zeros and ones, then converted into numbers representing something like speed or height. Then they are mapped in colored bar graphs that can be projected on a large TV screen.

In some cases, the NTSB will use the data to create animation of the flight. Animation showed the flight path of the water landing for US Airways flight 1549, nicknamed the Miracle on the Hudson.

The voice recorder captures four channels: the captain, the co-pilot, a general cockpit microphone and potentially an extra pilot.

At the NTSB, a team of perhaps a half-dozen investigators, including test pilots, will listen on headphones to the recording and develop a transcript, typically over three to five days. By law, the recordings are never released publicly, but transcripts are released by the time the board meets to decide what probably caused a crash.

The recordings carrying the pilots' final words are often difficult to listen to, both emotionally and for clarity. Whatever chaos is happening to the plane can drown out or blur the words.

Gormley compared the work to that of a trauma surgeon putting aside the emotional to figure out what happened.

"You're trying to get the job done," she said.

Besides hearing what the pilots and air-traffic controllers are talking about, the recorder captures all sorts of noises that can help decipher what happened to a plane. The NTSB's library of sounds includes gunshots. Analyzing the sounds can offer clues to engine speed or speed of tires on the ground.

"You're trying to make aviation safer," Gormley said of listening to the recordings. "We want to make sure it never happens again."



Copyright 2014 USATODAY.com

Read the original story: Flight recorders yield clues even after brutal crashes

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