Definition
Any instrument, mechanism, equipment, part, apparatus, appurtenance, or accessory — including communications equipment — that is used or intended to be used in operating or controlling an aircraft in flight, is installed in or attached to the aircraft, and is not part of the airframe, powerplant, or propeller.
Plain English
A piece of equipment fitted to the aircraft that helps fly or operate it, but is not part of the basic airframe, engine, or propeller. Things like radios, autopilots, and instruments are appliances.
Context Anchor
Seen in aircraft maintenance, airworthiness, and preflight document discussions, especially when deciding whether installed equipment is approved and working.
Derivation
From the Latin 'applicare', meaning 'to attach to' or 'apply to'. An appliance is literally something attached to the aircraft to serve a purpose — which matches the regulatory meaning closely.
Why Pilots Care
Required appliances must be installed and functioning for legal flight. Knowing what counts as an appliance (versus airframe or powerplant) matters when reviewing maintenance logs, minimum equipment lists, and airworthiness requirements.
Intuition Check
Do not read appliance as a household machine like a refrigerator or washing machine. In this FAA context, it means installed aircraft equipment or a device connected with operating the aircraft.
Example Sentence 1
The mechanic logged the new transponder as an appliance installation in the aircraft's maintenance records.
Example Sentence 2
A malfunctioning appliance such as the transponder must be repaired before the aircraft can be flown under instrument flight rules.