Definition
The change in an aircraft's speed over time during the takeoff or landing roll. Acceleration is the rate at which speed increases as the aircraft gains velocity for liftoff; deceleration is the rate at which speed decreases as the aircraft slows after touchdown or during a rejected takeoff. Both rates are influenced by thrust, drag, braking, runway surface, slope, wind, weight, and density altitude.
Plain English
How quickly the aircraft is speeding up on the takeoff roll or slowing down on the landing roll. A high rate means it gains or loses speed quickly. A low rate means it takes longer to reach takeoff speed or come to a stop.
Context Anchor
Seen in takeoff and landing performance discussions, especially when comparing runway length, aircraft weight, wind, runway slope, and surface condition.
Derivation
Accelerate comes from Latin accelerare, meaning 'to hasten' or 'speed up.' Decelerate is the opposite, formed by adding the prefix de- ('reverse of'). Rate simply means how fast something changes over time. Together: how quickly speed is increasing or decreasing.
Why Pilots Care
Affects the actual distance needed to reach rotation speed or come to a full stop, directly impacting safe runway selection.
Grounding Statement
On the runway, this is the difference between an airplane that quickly builds speed or slows down, and one that takes a long distance to do the same thing.
Intuition Check
Do not read “rate of acceleration/deceleration” as the airplane’s actual speed. It means how quickly that speed is changing.
Example Sentence 1
If the rate of acceleration during the takeoff roll feels noticeably slower than usual, the pilot should consider aborting before reaching the decision point.
Example Sentence 2
Standing water on the runway lowers the rate of deceleration and increases the distance needed to stop after landing.