Jack Boxes

BC-366 jack box (at right), with FL-8 range filter to its left
This is the classic AAF/AAC jack box, with volume control and several channels selectable by the crewman. COMP was for radio compass, INTER for interphone. Not all the positions had a radio transmit permission, but all could listen to the various radios listed on the switch. The "call" position was spring loaded to return to the interphone position.

There was a range filter associated with any flight crew position connected with navigation, like the pilot, copilot, and navigator. It was designed to facilitate the use of the radio range system, a network of electronic pathways laid out with beacons that directed the pilot between navigation points. Morse code letters A and N would alert the pilot to being left or right of the path, while a steady tone marked the center of the beam. In an era before squelch was introduced, selection of the 800 Hz filter (RANGE) would help ear fatigue immensely.

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