Solid-state Technology In Black Boxes

Solid-state recorders are considered much more reliable than
their magnetic-tape counterparts, according to Ron Crotty,
a spokesperson for Honeywell, a black-box manufacturer. 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). In
recorders made by L-3 Communications, the CSMU is
a cylindrical compartment on the recorder. The stacked memory
boards are about 1.75 inches (4.45 cm) in diameter and 1 inch
(2.54 cm) tall.

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. There
are sensors that detect acceleration, airspeed, altitude,
flap settings, outside temperature, cabin temperature and
pressure, engine performance and more. Magnetic-tape
recorders can track about 100 parameters, while solid-state
recorders can track more than 700 in larger aircraft.

All of the data collected by the airplane's sensors is sent
to the flight-data acquisition unit (FDAU) at the front of
the aircraft. This device often is found in the electronic
equipment bay under the cockpit. The flight-data acquisition
unit is the middle manager of the entire data-recording
process. It takes the information from the sensors and sends
it on to the black boxes.

Both black boxes are powered by one of two power generators
that draw their power from the plane's engines. One generator
is a 28-volt DC power source, and the other is a 115-volt,
400-hertz (Hz) AC power source. These are standard aircraft
power supplies, according to Frank Doran, director of
engineering for L-3 Communications Aviation Recorders.

Cockpit Voice Recorders

In almost every commercial aircraft, there are several
microphones built into the cockpit to track the conversations
of the flight crew. These microphones are also designed to
track any ambient noise in the cockpit, such as switches
being thrown or any knocks or thuds. There may be up to four
microphones in the plane's cockpit, each connected to the
cockpit voice recorder (CVR).

Any sounds in the cockpit are picked up by these microphones
and sent to the CVR, where the recordings are digitized and
stored. There is also another device in the cockpit, called
the associated control unit, that provides pre-amplification
for audio going to the CVR. Here are the positions of the
four microphones:

* Pilot's headset
* Co-pilot's headset
* Headset of a third crew member (if there is a third
crew member)
* Near the center of the cockpit, where it can pick up
audio alerts and other sounds

Most magnetic-tape CVRs store the last 30 minutes of sound.
They use a continuous loop of tape that completes a cycle
every 30 minutes. As new material is recorded, the oldest
material is replaced. CVRs that used solid-state storage can
record two hours of audio. Similar to the magnetic-tape
recorders, solid-state recorders also record over old
material.