Trim Runaway

Trim runaway is a serious—occasionally fatal—system malfunction. We look at what causes it and what you can do to handle it.

BTeter

Saturday, February 17, 2024 at 08:00 AM ET

Verified

Most modern yoke-mounted electric trim switches are actually two switches that must be activated together via a split, two-piece knob. (Photo: Cygnet Aerospace)

Key Takeaways:

The increasing prevalence of electric pitch trim (manual and autopilot-controlled) in general aviation cockpits is leading to a rise in incidents and accidents, particularly severe trim runaways.
A trim runaway occurs when the trim servo motor runs continuously due to various failures, such as stuck switches, autopilot malfunctions, or issues with artificial-feel systems.
If not immediately stopped, a trim runaway can generate extremely high control forces, making the aircraft difficult or impossible to control, and often leading to catastrophic outcomes.
Many pilots lack adequate training and awareness to quickly recognize and respond to a trim runaway, highlighting the critical need for understanding immediate action procedures and emergency simulation.

See a mistake? Contact us.

General aviation cockpits increasingly have electric pitch trim, both manual and autopilot-controlled, bringing a corresponding increase in incidents and accidents related to these systems. For manual electric trim, the trim servo-motor is activated by a switch on the control yoke. Manual electric trim aids flying as you needn’t break your visual concentration to reach for the trim wheel.

Newer, more sophisticated digital autopilots also have auto trim to complete the autopilot installation. Without the autopilot being able to trim the aircraft, the autopilot is only halfway flying the plane as you must manually adjust the trim. Configuration changes like dropping the gear and changing the flap settings are where auto trim shines.