Definition
An uncommanded, continuous movement of an aircraft trim system, typically electric pitch trim, that drives the trim toward a full nose-up or nose-down position without pilot input. The condition produces a steadily increasing control force that the pilot must oppose on the yoke or stick, and if not promptly identified and stopped, can lead to loss of control.
Plain English
The trim won't stop moving on its own. It keeps winding toward one extreme, and the controls get heavier and heavier until the pilot disconnects it.
Context Anchor
Encountered in emergency procedures for airplanes with electric trim or autopilot-connected trim systems.
Derivation
"Runaway" comes from the idea of something escaping control and continuing on its own — like a runaway horse or a runaway train. Applied to trim, it describes a system that has gotten away from the pilot and keeps moving without command.
Why Pilots Care
It produces rapid, unexpected pitch changes that can lead to loss of control if the pilot does not quickly isolate the trim circuit.
Intuition Check
Do not read runaway as the airplane physically leaving the pilot’s control all at once. Here it means the trim system itself is continuing or moving without the pilot’s intended command.
Example Sentence 1
During cruise, the pilot felt the nose pitching down and noticed the trim wheel spinning on its own — a classic trim runaway, which she stopped by disengaging the autopilot and pulling the trim circuit breaker.
Example Sentence 2
During the emergency procedure practice, the instructor simulated a trim runaway to show how to use the manual trim wheel for recovery.