Definition
The reduction in induced drag and the apparent increase in lift that occurs when an airplane is operating within approximately one wingspan above the ground during the takeoff roll and initial liftoff, allowing the airplane to become airborne at an airspeed below that required for sustained flight outside ground effect.
Plain English
When an airplane is very close to the ground during takeoff, the wing produces lift more efficiently than usual. This lets the airplane lift off at a slower speed than it can actually fly at once it climbs away from the ground.
Context Anchor
Encountered during the takeoff roll, initial liftoff, and the first few seconds after the wheels leave the runway.
Why Pilots Care
Pilots must recognize that an early liftoff in ground effect may leave the aircraft without enough climb performance to clear obstacles or accelerate safely, especially in high density altitude conditions.
Grounding Statement
Picture the airplane floating just above the runway after liftoff; while it stays low, it flies a little more efficiently, but that extra help fades as it climbs.
Intuition Check
Ground effect is not extra engine power, and it does not mean the airplane is ready to climb. It is a temporary airflow benefit from being close to the ground.
Example Sentence 1
On a hot day at a high-elevation airport, the instructor warned the student not to force the airplane off the runway, because lifting off in ground effect before reaching climb speed could leave them unable to climb away.
Example Sentence 2
After liftoff the pilot applied full power to climb out of ground effect and clear the departure obstacles.