Definition
Items installed on an aircraft that are not required by its type certificate or by regulation, but are added at the owner's or operator's choice. Their weight and arm must still be accounted for in the aircraft's weight and balance records whenever they are installed or removed.
Plain English
Extra equipment fitted to the aircraft that doesn't have to be there, but counts toward the airplane's weight and balance whenever it is installed.
Context Anchor
Seen on an airplane equipment list and during weight-and-balance calculations, especially when checking what items are installed on a specific airplane.
Derivation
Optional comes from a Latin word meaning “choice.” Equipment means the items used to outfit something for use. Together, the phrase points to equipment chosen in addition to the basic airplane setup.
Why Pilots Care
Must be weighed and accounted for if present because it changes total weight and may shift the center of gravity.
Intuition Check
Optional does not mean you can ignore it. In weight and balance, optional equipment is counted if it is installed, even though the airplane could exist without it.
Example Sentence 1
The owner added an autopilot as optional equipment, so the mechanic updated the weight and balance records to reflect the new empty weight.
Example Sentence 2
After installing a new autopilot, the mechanic updated the equipment list to show it as optional equipment.