Definition
Powered actuators within a helicopter's Automatic Flight Control System that move the collective pitch control to adjust the pitch angle of all main rotor blades together, changing total rotor thrust to control climb, descent, and power demand.
Plain English
Small powered devices that push or pull the up-and-down lever in a helicopter for the autopilot, raising or lowering the helicopter without the pilot moving it by hand.
Context Anchor
Seen in helicopter instrument procedures when describing stabilization systems and automatic flight control systems that can make control inputs for the pilot.
Derivation
Collective comes from Latin colligere, meaning to gather together — the control gathers the pitch change of all rotor blades at once. Servo comes from Latin servus (servant); a servo is a powered helper that moves a control on command. Together: the powered helpers that move the control which changes all blade pitches together.
Why Pilots Care
These servos enable hands-free altitude management in IMC, reducing pilot workload and improving precision during instrument approaches and holds.
Grounding Statement
When the system needs a small climb or descent correction, the collective control servos can physically help move the collective control system to make that correction.
Intuition Check
Do not read collective here as a group of servos. In this term, collective refers to the helicopter control that changes all main rotor blade angles together.
Example Sentence 1
With the AFCS engaged in altitude hold, the collective control servos made small adjustments to maintain 3,000 feet through light turbulence.
Example Sentence 2
During the ILS approach the collective control servos made small corrections to keep the helicopter on the glidepath.