What It Looks Like

The term black box as used to describe an item of avionics suggests that what goes on inside the box is inscrutable at best and nefarious at worst. The inscrutable perception is pretty much on the money, at least for those of us who are electron-challenged, but there is nothing sinister about the avionics found in the typical light general aviation aircraft, except perhaps the instruction manual.

In fact, black box generally refers to any piece of avionics equipment that is remotely mounted in the airplane; in other words, not mounted behind the indicator or display on the instrument panel. In many cases, the remotely mounted equipment is a nondescript metal box painted - you guessed it - black.

Some black boxes aren't black at all. A blind encoder technically qualifies for the black box label because it is remotely mounted, usually somewhere underneath the instrument panel close to the altimeter and transponder. And although it is painted high-visibility orange for search and rescue purposes, a remote-mounted aircraft emergency locator transmitter also can be considered a black box.

Traditional black boxes are indeed black. Remove the aft bulkhead at the rear of the baggage hold in a single-engine airplane or the nose cowl in a twin and, depending on the age of the aircraft and its avionics, you may see autopilot black boxes, including a processor, altitude sensor, and servos; converters that allow 28-volt avionics to work in a 14-volt airplane; gyros for compass systems; an older Storm- scope processor and DME computer; a glideslope receiver; and in a twin, a radar transmitter near the antenna.

Black boxes are gradually disappearing from the nooks and crannies of airplanes as equipment shrinks. Gone are the large, heavy, power-hungry radios that required two or more pieces of equipment, the indicator on the instrument panel and the remote-mounted power supply. The avionics equipment of old has been replaced by light, electrically frugal, incredibly capable computer processors and miniature circuitry that, in many cases, can all be contained inside the slender metal casings that extend behind the face of the panel-mounted radio or other type of avionics.