WIA Aircraft Component Standard Guide

In everyday speech, "aircraft component" can mean anything from a rivet to a complete wing. Regulators, manufacturers and maintenance organisations cannot afford that looseness, because the category an item falls into decides which approval it needs, which document accompanies it and who may install it. A records system that ignores these distinctions will sooner or later accept a part that should have been quarantined.

Aviation law in the United States and Europe recognises three products : the aircraft, the engine and the propeller. Each receives its own type certificate. Everything else that is installed on a product is a part or an appliance . The FAA's definitions (14 CFR Part 1) describe an appliance as an instrument, mechanism, piece of equipment, apparatus or accessory used in operating or controlling an aircraft in flight that is not part of an airframe, engine or propeller. A radio, a fuel quantity indicator or a cabin pressure controller is therefore an appliance; a wing rib or a landing-gear axle is a part of the airframe. European rules use the umbrella term "parts and appliances" in a similar way.