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What air investigators can learn from black boxes
Secrets of black boxes: What air investigators can learn from flight and voice recorders
By MATTHEW PENNINGTON
Associated Press
2014-03-29 06:22 AM

WASHINGTON (AP) -- One the world's foremost black box laboratories opened its doors to journalists Friday to provide some insight on how technicians can recover information from flight data and voice recorders, like those from missing Malaysia Airlines Flight 370.

It remains very uncertain if the recorders can be found in the depths of the vast Indian Ocean. But if the search succeeds, the information inside could help solve the mystery of why the jet flew so far off-course.

U.S. National Transportation Safety Board experts say even if the recorders have been submerged in deep water for an extended period, data can usually be recovered.

Here's some key points about how the information is retrieved, and what it can tell us:

--The black box, which is actually orange to aid visibility, consists a rectangular housing for electronics and a crash-hardened memory module that holds the data that investigators are looking for. Attached to the module is a pinger that sends out a signal to help locate the black box.

--While the battery that powers the pinger will run down after about one month, there's no definitive shelf-life for the data itself. The black boxes of an Air France flight that crashed in the Atlantic Ocean in 2009 were found two years later from a depth of more than 10,000 feet, (3,000 meters) and technicians were able to recover most of the information.

--If the box has been submerged in the sea, technicians will keep it submerged in fresh water to wash away the corrosive salt. As water may seep into the recorder, it must be carefully dried for hours or even days using a vacuum oven to prevent memory chips from cracking. The electronics and memory are checked, and any necessary repairs made. Chips are scrutinized under a microscope; even if one is cracked, often the data on it will have jumped onto another chip.

--Data is downloaded onto computer. The flight data recorder carries 25 hours of information, including prior flights within that time-span, which can sometimes provide hints about the cause of a mechanical failure on a later flight. The voice recorder has two hours of audio, of the captain, first officer and a microphone in the cockpit area.

--The data from the flight recorder, which comes as vast streams of binary code, is converted into a useable, time-linked form about hundreds of parameters, like altitude, air speed, pitch and engine thrust, to plot what happened on the airplane. An initial assessment of the data is provided to investigators within 24 hours, but analysis will continue for weeks more.

--An initial briefing on the voice recording is given to investigators by phone. A panel of six to eight experts then makes a meticulous transcript of the recording, which can take up a week. For privacy and legal reasons, the recording never leaves the laboratory, but parts of the transcript text may be made public if the investigation is advanced enough to put it into context.

--Technicians use a sound library to help them interpret ambient sounds from the recording: perhaps a doors opening, seats moving, an explosion or gunshot. The sound of the engine or gears can also help in analysis of the mechanics of the plane.

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