FAR 23.2140 — Airplane Trim

FAR 23.2140 is a Part 23 airworthiness standard that defines how a certificated airplane must behave when trimmed. The rule ensures the pilot can fly hands-off in normal flight regimes without fighting the controls.

The regulation breaks trim requirements into three categories:

• Lateral and directional trim: The airplane must hold trim with no further pilot input on primary or trim controls. This applies to Level 1, 2, and 3 airplanes in cruise, and to Level 4 airplanes in normal operations.
• Longitudinal trim: The airplane must hold pitch trim hands-off during climb, level flight, descent, and approach.
• Residual control forces: Any leftover stick or rudder force must not fatigue or distract the pilot during normal operations, or during likely abnormal or emergency operations, including a critical engine failure on multiengine airplanes.

Why it matters operationally: a properly trimmed airplane reduces pilot workload, improves precision in approach and cruise, and ensures the airplane remains controllable when something goes wrong — like an engine failure on a twin.