Definition
In aviation regulatory use, 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, engine, or propeller.
Plain English
Aircraft equipment that gets installed on or in the airplane but isn't part of the basic airframe, engine, or propeller. Things like radios, autopilots, transponders, and similar gear.
Context Anchor
Seen in FAA rulemaking, certification, and maintenance discussions about what equipment may be installed on an aircraft.
Derivation
From the Latin 'applicare,' meaning 'to attach or apply to.' The word originally meant something applied or added on. In aviation, it kept that flavor: equipment that is added to the aircraft rather than being part of its core structure.
Why Pilots Care
Appliances are regulated separately from the airframe and engine. They have their own certification, installation, and maintenance rules — which affects what can legally be installed, who can install it, and what paperwork is required.
Intuition Check
Do not read appliances as kitchen items or household machines. In FAA language, appliances means installed aircraft equipment such as instruments, radios, or other devices used in operating the aircraft.
Example Sentence 1
The new GPS unit is classified as an appliance, so its installation requires a logbook entry and an approval for return to service.
Example Sentence 2
During the preflight inspection the pilot verified that the required appliances such as the transponder and navigation radios were operational.