Which condition typically requires left rudder trim?

The condition that typically requires left rudder trim is during power addition. When power is added to the aircraft, particularly in a configuration like climb or go-around, the increased thrust from the engine can cause the aircraft to yaw to the right due to P-factor, torque effects, and slipstream effects. To counteract this right yaw, the pilot must apply left rudder input. Therefore, left rudder trim is often necessary to relieve the pilot of holding constant left rudder during these phases of flight.

In contrast, while deceleration may cause the aircraft to yaw in different ways depending on the specific aerodynamic changes, it does not directly require left rudder trim. Acceleration could also have less consistent yaw effects and is generally less related to the need for trim adjustment. Power reduction typically leads to a decrease in yawing moments, and while it may require right rudder input, it would not necessitate left rudder trim.