Definition
A gear that consists of only a portion, or sector, of a complete gear wheel — typically a pie-slice shape with teeth cut along the curved outer edge. It is used where the driven part only needs to rotate through a limited arc rather than a full revolution.
Plain English
A piece of a gear wheel — like a slice of a pie — with teeth on the curved edge. Because the part it drives only needs to swing back and forth through a small angle, a full round gear isn't needed.
Context Anchor
Seen in aircraft maintenance descriptions of mechanical systems that move controls, doors, or other parts through a limited range.
Derivation
From Latin sector, meaning 'a cutter' or 'a portion cut off,' from secare 'to cut.' In geometry, a sector is the pie-slice region of a circle. The gear is named after this shape — it looks like a slice cut from a full gear wheel.
Why Pilots Care
Provides precise, weight-saving movement for control surfaces while preventing over-travel that could damage the system.
Analogy
Picture a round clock face with gear teeth only along one curved slice of the edge. That slice can push or pull another toothed part without needing to turn in a full circle.
Intuition Check
Do not read “sector” here as an airspace sector or a geographic area. In this maintenance term, it means a partial section of a gear wheel.
Example Sentence 1
The technician inspected the sector gear in the flap drive assembly for worn or chipped teeth.
Example Sentence 2
Sector gears in the aileron actuator allow the surface to travel its full deflection range without adding unnecessary rotating mass.