Definition
A flight maneuver in which the aircraft is flown with its longitudinal axis at an angle to the flight path, used to lose altitude rapidly without gaining airspeed. The pilot lowers one wing with aileron while applying opposite rudder, so the aircraft descends along its original ground track but with the fuselage angled across the flight path. The increased fuselage exposure to the relative wind creates drag, steepening the descent.
Plain English
A way of dropping height quickly without speeding up. The pilot tips one wing down and pushes the opposite rudder pedal, which makes the airplane fly slightly sideways through the air. This crossed-up shape creates extra drag, so the aircraft sinks faster while still tracking toward the same point on the ground.
Context Anchor
Most often encountered during approach and landing when the airplane is too high and the pilot needs to lose altitude without speeding up.
Derivation
The word slip describes air slipping past the side of the fuselage rather than flowing cleanly nose-to-tail. Forward refers to the fact that the aircraft's ground track stays aligned with the runway or intended path, even though the nose is pointed off to one side.
Why Pilots Care
Allows rapid altitude loss on short or obstructed approaches while keeping the runway in view and avoiding excessive speed buildup.
Grounding Statement
Picture the airplane aimed a little sideways into the airflow while still tracking toward the runway, so the extra drag helps it sink faster.
Intuition Check
Forward slip does not mean the airplane is slipping forward out of control. Here, it means a deliberate cross-control maneuver used to descend more steeply while keeping the desired path over the ground.
Example Sentence 1
Realizing he was too high on final, the pilot lowered the left wing and applied right rudder, entering a forward slip to lose altitude before crossing the threshold.
Example Sentence 2
In the forward slip the left aileron was lowered and right rudder applied to keep the nose pointed at the runway numbers.