A Black box is a small device that is built into an airplane, to improve
air security, by recording important data about the airplane.
Also called: Flight Recorder or CSMU (Crash-Survivable Memory Unit)
What it looks like
A black box is not black at all- it is bright neon orange, so it
can be found more easily by divers and other investigators digging through
the wreckage.
It is basically a square-shaped, shock resistant, Fire resistant, water
proof, Pressure resistant box. It is by no means indestructible (nothing
is), but putting a dent in a black box is not easy. Besides - it is placed
in or near the tail of the plane (at least in commercial airliners, chances
of it breaking are limited.
Why it is called a black box
The black boxes might have been black once, but the most likely reason for
the box being called black is that it is usually charred after the fire
that accompanies most crashes
How it is built
(from outside to inside)
- The black box
- The memory / tape banks:
- Shell - Titanium / Stainless steel - waterproof, shockproof,
withstanding extreme heat. About 0.3 inches (0,76 cm) thick
- Temperature Shield - Dry-silica material. About 1.1 inch
(3 cm) thick - protects the recorders from heat after the crash
- Aluminium housing - Another layer to make sure that the package
stays water-proof.
Another part of the box is a small beacon activated if it comes in contact
with water. The beacon sends out ultrasonic waves that can be traced with
a sonar
What it is used for
The FAA (Federal Aviation Administration) and their counterparts in non-US
countries use the Black Box to try to determine the reason for planes
crashing. Even though each of those boxes cost between $10,000 and $20,000
each, they have led to reasons being found for many airline crashes that otherwise
would have been unsolved
What it records
Most Black Boxes contain two elements: an FDR (Flight Data Recorder) and
a CVR (Cockpit Voice Recorder).
- FDR
- CVR
- Communications with the Flight Tower
- Sounds inside the cockpit (not just voice, but also buttons being
clicked on and off etc) from up to four microphones
How it records it
Most black boxes still use magnetic tape (sorta like you find in VCRs
and Music Cassettes), but more and more of them are using solid state memory
(i.e Flash Memory or the like), because it is more resistent to heat, and
because they have no movable parts. Another advantage of solid state memory
is that it can track up to 700 different data flows, while the tape version
only can hold about 150.
The black boxes aren't replaced every flight- The tape versions store about
30 minutes of audio data, and the tape goes in a loop, so the oldest data
is overwritten. The same goes for the flight data, but usually, between one
and four hours of data is kept. Solid-state memory versions do the same
thing, but can store more information (about 2 hrs of audio and 25 hours of
flight data)
The data is gathered from the sensors that are all around the airplane,
plus a bunch of microphones in the cockpit
How the data is extracted
There is a port on the Black box which looks remarkably much like a parallel
port. From this port, a handheld data extraction device can read the data
directly from the box. If this port has been damaged (happens quite often),
the whole box has to be (partially) disassembled. If all data connectors
are busted, the whole box must be taken apart, and the data must be read
directly from the memory.
History
The idea of a black box has been with us since the birth of Aviation.
The Wright brothers (who were the first to fly a plane for more than a minute)
used a device that recorded propeller rotations, to analyze how to improve
their plane.
The use of black boxes became normal shortly after the Second World War
ended.
source: L3 aviation recorders (http://www.l-3ar.com/)
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