Definition
The intentional use of a forward or sideslip while wing flaps are deployed, typically during the approach and landing phase to increase descent rate or correct for crosswind. Some airplanes prohibit or place limitations on this maneuver because the deflected flaps can disturb airflow over the horizontal tail, causing pitch changes, buffeting, or reduced elevator effectiveness. Pilots must consult the Airplane Flight Manual or Pilot's Operating Handbook for the specific aircraft's limitations before slipping with flaps extended.
Plain English
Flying the airplane in a slip (one wing low, opposite rudder) while the flaps are down. Some airplanes handle this fine; others have warnings against it because the flaps can mess up airflow over the tail. Always check the manual before doing it.
Context Anchor
Encountered during approach and landing training, especially when discussing intentional slips used to lose altitude without increasing airspeed.
Derivation
Slip comes from the idea of sliding sideways. In aviation, a slip means the airplane is deliberately flown slightly sideways through the air. Extended means put out or moved from the normal position; here, the flaps have been lowered from the wing.
Why Pilots Care
Provides a reliable way to lose altitude rapidly on short or obstructed approaches while staying within airspeed limits; the pilot must remain aware of the higher sink rate and possible changes in control feel.
Grounding Statement
Picture being high on final approach with the flaps already down: a slip might help lose altitude, but only if that airplane is approved to do it.
Intuition Check
Do not read “slip” here as an accident or mistake; it is a deliberate flight maneuver. Do not read “extended” as meaning the flaps are longer; it means the flaps are lowered or deployed.
Example Sentence 1
Before practicing short-field landings, the instructor reviewed the POH note on slips with flaps extended to confirm the maneuver was approved in that airplane.
Example Sentence 2
The instructor demonstrated a slip with flaps extended so the student could feel how quickly the airplane descends while staying coordinated on rollout.