Definition
Systems and equipment installed in an aircraft beyond what is required for certification or for the specific operation being flown. These items are not mandatory under the regulations or the aircraft's type certificate but are added by the manufacturer or owner to expand capability, improve comfort, or support particular missions. Their installation, operation, and any associated limitations are described in a supplement to the Pilot's Operating Handbook (POH) or Airplane Flight Manual (AFM).
Plain English
Extra gear fitted to an aircraft that wasn't required to make it legal to fly, but adds useful features. Each piece of optional kit comes with its own section in the handbook explaining how to use it and any rules that go with it.
Context Anchor
Seen in the Supplements section of a Pilot’s Operating Handbook or Aircraft Flight Manual, especially when checking what installed equipment applies to the specific aircraft you are flying.
Derivation
Optional comes from a Latin word meaning “to choose.” In this aviation use, it points to equipment that was chosen or added for a particular aircraft instead of being included on every aircraft of that model.
Why Pilots Care
Determines which installed items must be functional before flight and affects weight-and-balance or performance calculations.
Intuition Check
Optional does not mean unimportant or safe to ignore. It means not installed on every aircraft; if it is installed on the aircraft you fly, its instructions and limitations apply.
Example Sentence 1
Before flying the new-to-her aircraft, she reviewed Section 9 to understand the optional systems and equipment installed, including the autopilot and the supplemental oxygen system.
Example Sentence 2
During preflight the pilot confirmed that all optional systems and equipment were operational before departure.