Definition
Any force acting opposite to the direction of motion that slows an aircraft down. During landing, retarding forces include aerodynamic drag, rolling friction between the tires and runway, and braking friction from the wheel brakes.
Plain English
A force that pushes against the airplane's motion and slows it down. On landing, this is the combined slowing effect of air drag, tire friction, and the brakes.
Context Anchor
Seen in landing performance discussions, especially when estimating landing roll and stopping distance after touchdown.
Derivation
From the Latin retardare, meaning 'to slow down' or 'to hinder.' A retarding force is literally a force that holds the aircraft back from continuing forward.
Why Pilots Care
Retarding forces directly determine how much runway is required to stop safely and affect decisions about landing distance available.
Analogy
It is like squeezing the brakes on a bicycle: the bicycle is still moving forward, but the braking force acts against that motion and slows it down.
Grounding Statement
After touchdown, the airplane keeps rolling until the forces slowing it are large enough and act long enough to bring it to a stop.
Intuition Check
Do not read “retarding” as simply “delaying.” Here it means “slowing the airplane by acting against its motion.”
Example Sentence 1
On a wet runway, the retarding force from the brakes is reduced because the tires can't grip as well.
Example Sentence 2
Reverse thrust adds to the retarding force and shortens the distance needed to stop on a wet runway.