Definition
A change in velocity in which speed is increasing or the direction of motion is changing such that the resulting force on the aircraft and its occupants acts in the same general direction as the motion. In flight, positive acceleration is most commonly experienced as an increase in airspeed during takeoff or as the upward (positive G) loading felt when pulling back on the controls in a climb or turn.
Plain English
A speed-up. The aircraft is gaining speed, or it is being pushed in a way that adds force in the direction it is already moving.
Context Anchor
Seen in basic aerodynamics and Newton’s laws when explaining how force changes an aircraft’s motion.
Derivation
From the Latin 'accelerare,' meaning 'to hasten' or 'to speed up.' 'Positive' simply marks the direction of the change as an increase rather than a decrease. Together they describe motion that is gaining speed.
Why Pilots Care
Recognizing positive acceleration helps pilots anticipate changes in airspeed and control loading during thrust application.
Grounding Statement
If the aircraft’s speed is increasing in the direction being measured, it is experiencing positive acceleration in that direction.
Intuition Check
Positive does not mean “good” here; it means increasing or acting in the chosen direction of measurement. Acceleration does not only mean engine power; it means a change in velocity.
Example Sentence 1
During the takeoff roll, the aircraft undergoes positive acceleration as thrust overcomes drag and airspeed builds toward rotation.
Example Sentence 2
Positive acceleration during the takeoff roll increases groundspeed until rotation speed is reached.