Definition
A flight control system that supports and refines the action of the primary flight controls. Secondary controls include wing flaps, leading edge devices, spoilers, and trim systems, and are used to improve aircraft performance characteristics or to relieve the pilot of excessive control forces.
Plain English
These are the extra controls that help the main controls do their job better. They reduce the workload on the pilot, change the wing's lift and drag for takeoff and landing, or hold the aircraft steady so the pilot doesn't have to keep pulling or pushing on the yoke.
Context Anchor
Seen when learning aircraft flight controls, checking the cockpit controls during preflight, and reading an aircraft handbook about flaps, trim, spoilers, or other control equipment.
Derivation
Secondary comes from the Latin secundus, meaning 'following' or 'second in order.' These controls are 'secondary' not because they are less important, but because they assist and follow the action of the primary controls (ailerons, elevator, rudder).
Why Pilots Care
Use of the secondary control system lets the pilot adjust lift and drag for takeoff, landing, and cruise without fighting heavy control forces or exceeding structural limits.
Intuition Check
Secondary does not mean optional or unimportant here. It means the controls that support the main flight controls by changing the airplane’s setup or reducing the force the pilot must hold.
Example Sentence 1
Before landing, the pilot configured the secondary control systems by extending the flaps and trimming for the approach speed.
Example Sentence 2
Trimming the elevator tab via the secondary control system relieved control pressure during a long cruise segment.