Black box

A black box is a system where we have a well defined understanding of its inputs and output characteristics, but no idea what's going on inside.

There are several main senses:

"Black boxes" in avionics and other systems

The classic black box is a "line replaceable unit," or LRU. Black boxes are usually radios or other auxiliary equipment for a complex engineered system like an airplane or ship. Black boxes speed up repair, because they can be replaced quickly, restoring the big system to service. They also reduce the cost of systems, and increase the quality, by spreading development costs of the type of unit over different models of vehicles.

Black boxes are designed to specifications. The specification defines the inputs and outputs. It also defines the tools to replace the unit (usually nothing more than a #2 Phillips-head screwdriver), and the bulk and weight (they always need to be carried by one man, and fit through a door, if possible). There are also requirements for flammability, unwanted radio emissions, resistance to damage from fungus, static electricity, heat, pressure, humidity, condensation drips, vibration, radiation and other environmental measurements.

Many black boxes for commercial aircraft are designed according to specifications from Airline Radio Incorporated, affectionately called "ARINC." ARINC is a company owned by a number of airlines, that sells specifications and sets standards. Black boxes are also defined by manufacturers like Airbus and Boeing, or various military organizations.

LRUs are painted crackle-black to more efficiently radiate and convect heat away from the unit.

"Black box" flight data recorders

Flight data recorders, called "black boxes" by the news media, record aircraft and pilot behavior in order to analyze accidents.

The main purpose of the device is to reduce the manufacturer's liability by correctly assigning blame to the failing assemblies or persons. The famous, secondary use is to analyze accidents to prevent future failures.

Traditional black boxes use potentiometers attached to strings. The strings are actually steel wire, bolted to the controls and flight surfaces. As the surfaces move, the resistances of the pots change, changing the frequency of an oscillator. The oscillator's electronic howl is wired to a recorder. The howl is better than just recording a voltage because the howl cannot be affected as easily by stray currents or magnetic fields. The howls, along with the pilot's incoming and outgoing audio, are recorded on a continuous loop of magnetic tape or wire.

Black boxes are often poorly maintained, because they are not critical to flight. There is a growing sentiment that they should be reliable, solid-state digital systems. Additionally, since they are often crushed into unreadable pieces, or never located, there is a move to make them self-ejecting, and brightly colored, with radio and sonar beacons.

External Links

• The Black Box: An Australian Contribution to Air Safety (http://www.dsto.defence.gov.au/corporate/history/jubilee/blackbox)
• Flight Data Recorders: How They Work and What They Reveal (http://abcnews.go.com/sections/scitech/DailyNews/blackbox011114)
• How Black Boxes Work (http://www.howstuffworks.com/black-box.htm) (Seven page article with links)

"Black boxes" in philosophy and mathematics

The term is important in philosophical contexts, because various philosophers have proposed black box theories[?] for various fields. Probably the most prominent such theory is the so called black box theory of consciousness, which states that the mind is fully understood once the inputs and outputs are well defined, and generally couples this with a radical skepticism about the possibility of ever describing what goes on inside the mind.

The "Black Box" Game

Black Box[?] is a game which simulates shooting lasers into a black box to deduce the locations of mirrors hidden inside. It has been sold as a board game, and there are also numerous computer implementations for many different platforms.

The Black Box in Phone Phreaking

The Black Box was a particular kind of device built by phone phreaks during the 1960s and 1970s (as distinguished from blue boxes and red boxes) in order to defeat toll charges, and specifically to block the supervision signal sent by the receiving telephone handset when the call was answered at the receiving end of the call. In other words, the box fooled the phone company into thinking no one had answered at the receiving end, and therefore billing was never started on the call. Participating in a black box call meant talking between rings, since the phone co. would continue to send rings (AC current) through the line which was heard as a loud buzzing noise. Few people build or use Black Boxes anymore, given that the cost of long-distance telephone calls has come down dramatically since the 1970s.

See also

• White box[?]
• Black Box[?], the theatrical term.
• Blackbox, the window manager