After a Crash

Although they are called "black boxes," aviation recorders
are actually painted bright orange. This distinct color,
along with the strips of reflective tape attached to the
recorders' exteriors, help investigators locate the black
boxes following an accident. These are especially helpful
when a plane lands in the water. There are two possible
origins of the term "black box": Some believe it is because
early recorders were painted black, while others think it
refers to the charring that occurs in post-accident fires.

Underwater Locator Beacon
In addition to the paint and reflective tape, black boxes are
equipped with an underwater locator beacon (ULB). If you look
at the picture of a black box, you will almost always see
a small, cylindrical object attached to one end of the device.
While it doubles as a handle for carrying the black box, this
cylinder is actually a beacon.

If a plane crashes into the water, this beacon sends out
an ultrasonic pulse that cannot be heard by human ears but is
readily detectable by sonar and acoustical locating equipment.
There is a submergence sensor on the side of the beacon that
looks like a bull's-eye. When water touches this sensor, it
activates the beacon.

The beacon sends out pulses at 37.5 kilohertz (kHz) and can
transmit sound as deep as 14,000 feet (4,267 m). Once the
beacon begins "pinging," it pings once per second for 30
days. This beacon is powered by a battery that has a shelf
life of six years. In rare instances, the beacon may get
snapped off during a high-impact collision.

In the United States, when investigators locate a black box
it is transported to the computer labs at the National
Transportation Safety Board (NTSB). Special care is taken in
transporting these devices in order to avoid any (further)
damage to the recording medium. In cases of water accidents,
recorders are placed in a cooler of water to keep them from
drying out.

"What they are trying to do is preserve the state of the
recorder until they have it in a location where it can all be
properly handled," Doran said. "By keeping the recorder in
a bucket of water, usually it's a cooler, what they are doing
is just keeping it in the same environment from which it was
retrieved until it gets to a place where it can be adequately
disassembled."

Retrieving Information
After finding the black boxes, investigators take the
recorders to a lab where they can download the data from the
recorders and attempt to recreate the events of the accident.
This process can take weeks or months to complete. In the
United States, black-box manufacturers supply the NTSB with
the readout systems and software needed to do a full analysis
of the recorders' stored data.

If the FDR is not damaged, investigators can simply play it
back on the recorder by connecting it to a readout system.
With solid-state recorders, investigators can extract stored
data in a matter of minutes. Very often, recorders retrieved
from wreckage are dented or burned. In these cases, the
memory boards are removed, cleaned up and a new memory
interface cable is installed. Then the memory board is
connected to a working recorder. This recorder has special
software to facilitate the retrieval of data without the
possibility of overwriting any of it.

A team of experts is usually brought in to interpret the
recordings stored on a CVR. This group typically includes
a representative from the airline, a representative from the
airplane manufacturer, an NTSB transportation-safety
specialist and an NTSB air-safety investigator. This group
may also include a language specialist from the Federal
Bureau of Investigation and, if needed, an interpreter. This
board attempts to interpret 30 minutes of words and sounds
recorded by the CVR. This can be a painstaking process and
may take weeks to complete.

Both the FDR and CVR are invaluable tools for any aircraft
investigation. These are often the lone survivors of airplane
accidents, and as such provide important clues to the cause
that would be impossible to obtain any other way. As
technology evolves, black boxes will continue to play
a tremendous role in accident investigations.