Slip (aerodynamics)

Inexperienced or inattentive pilots will often enter slips unintentionally during turns by failing to coordinate the aircraft with the rudder.

This is especially dangerous if there are nearby obstructions under the climb path and the aircraft is underpowered or heavily loaded.

These methods are also commonly employed when flying into farmstead or rough country airstrips where the landing strip is short.

[1] Without flaps or spoilers it is difficult to increase the steepness of the glide without adding significant speed.

This excess speed can cause the aircraft to fly in ground effect for an extended period, perhaps running out of runway.

[2] Aerodynamically these are identical once established, but they are entered for different reasons and will create different ground tracks and headings relative to those prior to entry.

Forward-slip is used to steepen an approach (reduce height) without gaining much airspeed,[3] benefiting from the increased drag.

The sideslip moves the aircraft sideways (often, only in relation to the wind) where executing a turn would be inadvisable, drag is considered a byproduct.

[6] A forward-slip is useful when a pilot has set up for a landing approach with excessive height or must descend steeply beyond a tree line to touchdown near the runway threshold.

Assuming that the plane is properly lined up for the runway, the forward slip will allow the aircraft track to be maintained while steepening the descent without adding excessive airspeed.

The horizontal component of lift is directed toward the low wing, drawing the airplane sideways.

In case of crosswind, the wing is lowered into the wind, so that the airplane flies the original track.

This allows the wheels to be constantly aligned with the track, thus avoiding any side load at touchdown.

The sideslip method for crosswind landings is not suitable for long-winged and low-sitting aircraft such as gliders, where instead a crab angle (heading into the wind) is maintained until a moment before touchdown.

Aircraft manufacturer Airbus recommends sideslip approach only in low crosswind conditions.