After the crash, they didn't find a single body for five
days. Even with military and civilian personnel frantically scouring the seas,
it was as if Air France Flight 447 had simply vanished over a remote area of
ocean 600 miles from Brazil -- with 228 people onboard. It didn't happen in the
early days of the airline industry; it occurred in 2009, on a fancy modern
aircraft controlled by a competent company.
Airplane accidents are statistical rarities. But when they
happen, they're often fatal, and people want answers as to why their loved ones
died.
There are usually 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. Following any airplane accident in the U.S., safety
investigators from the National Transportation Safety Board (NTSB) immediately
begin searching for the aircraft's black boxes.
It took investigators nearly two years to find the FDR from
Flight 447. The box had not only survived impact, but also being submerged
under nearly 13,000 feet of salty, corrosive seawater. In the end, the data
proved that pilot error had contributed to a stall that eventually caused the
crash.
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.
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 log much more information about an aircraft's operation.
Older black boxes used magnetic tape, a technology that was
first introduced in the 1960s. 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. These days, black boxes use solid-state memory boards, which came
along in the 1990s.
Solid-state recorders are considered much more reliable than
their magnetic-tape counterparts. Solid state uses stacked arrays of memory
chips, so they don't have moving parts. With no moving parts, there are fewer
maintenance issues and a decreased chance of something breaking during a crash.
Data from both the CVR and FDR is stored on stacked memory
boards inside the crash-survivable memory unit (CSMU). The memory boards have
enough digital storage space to accommodate two hours of audio data for CVRs
and 25 hours of flight data for FDRs.
Airplanes are equipped with sensors that gather data such as
acceleration, airspeed, and altitude, flap settings, outside temperature,
engine performance, and cabin temperature and pressure. Magnetic-tape recorders
can track about 100 parameters, while solid-state recorders can track a lot
more.