Definition
A sideways force applied to the landing gear when the airplane's tires touch down or roll while the longitudinal axis is not aligned with the direction of travel. Side load stresses the gear structure, tires, and wheel assemblies laterally rather than along their designed vertical and forward axes.
Plain English
The sideways pushing force on the wheels and gear when the airplane is moving in one direction but pointing in another. The tires get scrubbed sideways instead of rolling cleanly straight ahead.
Context Anchor
Seen in crosswind landing discussions, especially during touchdown and the after-landing roll.
Derivation
“Load” can mean a weight or burden, but in aviation it often means a force that a part of the airplane must carry. “Side” tells you the force is coming from the side rather than from straight ahead or straight down.
Why Pilots Care
High side loads can damage landing-gear components or cause loss of directional control.
Intuition Check
Side load does not mean cargo placed on one side of the airplane. Here, “load” means force, and “side” means the force is pushing across the airplane instead of along its forward movement.
Example Sentence 1
Touching down in a crab without straightening the nose puts a heavy side load on the main gear.
Example Sentence 2
Strong crosswinds increase side load if the airplane is allowed to weathervane during the rollout.