A slip in aviation is a maneuver where a pilot intentionally flies the aircraft slightly sideways through the air. This creates extra aerodynamic drag, which is useful for losing altitude quickly or for aligning the plane with the runway during a crosswind landing. Pilots create a slip by crossing the flight controls: banking the wings one direction with the ailerons while pressing the opposite rudder pedal to point the nose the other way.
How a Slip Works Aerodynamically
In normal, coordinated flight, the nose of the airplane points in the same direction the airplane is traveling. Air flows smoothly along the fuselage from front to back. In a slip, the fuselage is angled to the oncoming air, exposing the broad side of the airplane to the wind. This dramatically increases drag, the same way holding your hand flat out a car window catches more air when you tilt it sideways.
The pilot sets up a slip by deflecting the ailerons in one direction (banking the wings) and applying opposite rudder. For example, banking left while pressing the right rudder pedal. The ailerons tilt the airplane, and the rudder keeps the nose pointed away from the direction of the bank. The bigger the control deflections, the more drag the airplane produces and the faster it descends.
Forward Slips: Losing Altitude Fast
A forward slip is the most common use of this maneuver. The goal is to descend steeply without the airplane picking up speed. This matters when a pilot finds themselves too high on approach to the runway and needs to get down quickly. Rather than circling around for another attempt, a forward slip lets the pilot shed that extra altitude on the spot.
The technique involves reducing engine power to idle while banking and applying full opposite rudder. The airplane’s fuselage turns at an angle to its flight path, acting like a big air brake. The steeper the bank and the more rudder applied, the higher the rate of descent. Throughout the maneuver, the airplane continues tracking toward the runway, just doing so in a high-drag, nose-offset attitude. Once at the desired altitude, the pilot releases the rudder pressure and levels the wings to resume normal flight.
Forward slips are especially valuable in aircraft without flaps, or in situations where flaps alone aren’t enough to steepen the descent. Every pilot trains for this maneuver because it can turn an unstable approach into a good landing without going around.
Side Slips: Handling Crosswinds
A side slip (sometimes called the “wing-low” method) solves a different problem: landing when the wind is blowing across the runway. Without correction, a crosswind pushes the airplane sideways, making it drift off the runway centerline. A side slip counteracts that drift.
The pilot banks into the wind using the ailerons, which stops the airplane from drifting sideways. At the same time, opposite rudder keeps the nose pointed straight down the runway. The result is an airplane that tracks along the centerline with its fuselage aligned with the runway, even though its wings are slightly tilted. The upwind main landing gear touches down first, followed by the downwind gear. Many pilots use a combined technique on final approach: they initially point the nose into the wind (called crabbing) to stay on the centerline, then transition to a side slip just before touchdown so the wheels are aligned with the runway.
Because the side slip increases drag, pilots typically add a bit of extra power to maintain their desired descent rate. This is one key difference from a forward slip, where the whole point is maximum descent.
The Difference Between Forward and Side Slips
The control inputs are nearly identical. What changes is the airplane’s orientation relative to the runway. In a forward slip, the airplane’s nose is angled away from the runway heading, and the flight path stays aimed at the runway. The pilot is using the maneuver purely to descend. In a side slip, the nose stays pointed straight down the runway, and the bank angle compensates for crosswind drift. Same crossed controls, different purpose.
Slips vs. Skids
A slip and a skid are often confused because both involve uncoordinated flight, meaning the airplane isn’t flying straight through the air. The difference is which way the airplane is displaced. In a slip, the airplane slides toward the inside of a turn (the low wing side). In a skid, the airplane slides toward the outside of the turn.
You can tell which one is happening by looking at the inclinometer, a small ball in a curved tube on the instrument panel. If the ball slides to the left, you’re slipping left. The standard correction is to “step on the ball,” pressing the rudder pedal on the same side the ball has moved to.
The safety distinction matters. If an airplane stalls during a slip, it tends to roll toward wings-level, away from a spin. The outside (higher) wing stalls first, and the resulting roll actually helps recover the airplane. If an airplane stalls during a skid, the inside (lower) wing stalls first, and the airplane rolls sharply into the turn. This is the classic entry into an incipient spin, one of the most dangerous situations in low-altitude flying. This is why instructors emphasize that skidding turns near the ground are far more hazardous than slipping turns.
Aircraft Limitations on Slipping
Not all aircraft handle slips the same way, and some have specific restrictions when flaps are extended. The Cessna 172 is a good example of how these limitations have evolved. The 1956 model’s manual flatly prohibited slips during full-flap approaches because pilots could encounter a sudden nose-down pitch at certain airspeeds and slip angles. By 1977, Cessna had softened the language for the 172N model, warning that steep slips with flap settings greater than 20 degrees could cause the elevator to oscillate. Late-model 172S aircraft carry a similar advisory.
The underlying issue is that the disrupted airflow from the fuselage being sideways to the wind can interact with extended flaps in unexpected ways, sometimes blanking the airflow over the tail and causing pitch or control instability. The severity depends on the specific airplane, its flap design, airspeed, and how the weight is distributed. Your airplane’s operating handbook is the definitive guide on what’s allowed. Some aircraft slip beautifully with full flaps, while others require caution or prohibit it entirely.
When Pilots Use Slips in Practice
Slips come up regularly in everyday flying. A pilot flying a visual approach who ends up slightly high might use a brief forward slip to get back on the correct glide path. A pilot landing at a small grass strip with gusty crosswinds will almost certainly use a side slip on short final. Student pilots practice both types extensively, because they build rudder coordination skills and prepare for the inevitable day when the approach doesn’t go as planned.
Slips are also a backup for mechanical situations. If flaps fail in the extended or retracted position, a forward slip can substitute for the drag the flaps would have provided. In gliders, which have no engine to manage energy, slips are a routine part of the landing toolkit.