Black Boxes

On January 31, 2000, Alaska Airlines Flight 261 departed
Puerto Vallarta, Mexico, heading for Seattle, WA, with
a short stop scheduled in San Francisco, CA. Approximately
one hour and 45 minutes into the flight, a problem was
reported with the plane's stabilizer trim. After a 10-minute
battle to keep the plane airborne, it plunged into the
Pacific Ocean off the coast of California. All 88 people
onboard were killed.

With any airplane crash, there are many unanswered questions
as to what brought the plane down. Investigators turn to the
airplane's flight data recorder (FDR) and cockpit voice
recorder (CVR), also known as "black boxes," for answers. In
Flight 261, the FDR contained 48 parameters of flight data,
and the CVR recorded a little more than 30 minutes of
conversation and other audible cockpit noises.

Following any airplane accident in the United States, safety
investigators from the National Transportation Safety Board
(NTSB) immediately begin searching for the aircraft's black
boxes. These recording devices, which cost between $10,000
and $15,000 each, reveal details of the events immediately
preceding the accident. In this article, we will look at the
two types of black boxes, ­how they survive crashes, and how
they are retrieved and analyzed.

Recording and Storage

The Wright Brothers pioneered the use of a device to record
propeller rotations, according to documents provided by L-3
Communications. However, the widespread use of aviation
recorders didn't begin until the post-World War II era. Since
then, the recording medium of black boxes has evolved in
order to record much more information about an aircraft's
operation.

Although many of the black boxes in use today use magnetic
tape, which was first introduced in the 1960s, airlines are
moving to solid-state memory boards, which came along in the
1990s. Magnetic tape works like any tape recorder. The Mylar
tape is pulled across an electromagnetic head, which leaves
a bit of data on the tape.

Black-box manufacturers are no longer making magnetic tape
recorders as airlines begin a full transition to solid-state
technology.