Definition
A mechanical device consisting of a threaded shaft (the screw) turning inside a matching threaded sleeve (the nut), used to convert rotary motion into precise linear motion for moving, positioning, or lifting heavy aircraft components. Jackscrews are commonly used to drive trim surfaces such as the horizontal stabilizer, to extend and retract certain landing gear, and to operate flight control surfaces or doors.
Plain English
A long screw that, when turned, slowly pushes or pulls something heavy in a straight line. Spinning the screw moves the attached part forward or back in a controlled way.
Context Anchor
Seen in aircraft maintenance when inspecting trim systems, flap mechanisms, actuators, and screw-type lifting or positioning devices.
Derivation
From 'jack' (a lifting device, as in a car jack) and 'screw' (a threaded shaft). The name reflects what it does: it lifts or moves a load using a screw thread instead of hydraulic pressure.
Why Pilots Care
Proper function ensures stable pitch control; failure can lead to loss of trim authority.
Analogy
Think of a vise on a workbench. Turning the handle slowly drives the jaws closed with enormous force. A jackscrew works the same way, but the moving part is attached to an aircraft component instead of clamping wood.
Intuition Check
A jackscrew is not just any screw on the aircraft. It is a screw mechanism designed to move or hold a part by turning.
Example Sentence 1
During the inspection, the technician checked the horizontal stabilizer jackscrew for wear and applied fresh grease to the threads.
Example Sentence 2
Excessive play in the jackscrew can cause unstable pitch trim during flight.