Learn › Maneuvers › Forward Slip to a Landing

Forward Slip to a Landing

You are already at idle with the flaps out and you are still too high. The forward slip is the last tool between that approach and a go-around — a way to trade drag for descent without trading it for speed.

Takeoffs, Landings and Go-Arounds — FI.VII.M

Why the slip exists

High approaches arrive for ordinary reasons. An early base turn to stay clear of traffic, less headwind than the forecast promised, a pattern flown tighter than the one before it — none of that is sloppy flying, and all of it puts the runway further down the windshield than you want it. Pitching the nose over does bring you down, but it hands you airspeed you have to give back in the flare, and the float that follows eats the runway you were trying to save.

That is the corner the forward slip was built for. It is not a substitute for going around, which is always available and never wrong, but it is often what stands between salvaging the approach you have and starting the whole thing over. It is also how you get into a short field with trees or wires on the approach end: cross them high, then come down on the far side.

What the airplane is actually doing

A slip is cross-controlled flight, held on purpose. You bank one way with aileron and stop the turn with opposite rudder. The wings want to turn and the rudder refuses, so the airplane keeps going the direction it was already going while pointing somewhere else. The deflected controls add drag, but the bigger effect is the fuselage: it is now flying partly sideways, presenting its whole flank to the air instead of its nose. That is form drag, and a lot of it.

Cross-controlled is a loaded phrase, so separate the two places it turns up in your training before you go any further. The forward slip is cross-controlled flight you fly yourself, on final, as a matter of routine. The cross-controlled stall is a different thing: a demonstration your instructor sets up and flies at a safe altitude so you can see what an airplane does when it is stalled out of coordination. Spin entries and recoveries belong to that same category — instructor-demonstrated, high, and briefed. Nothing in this lesson asks you to go find either one on your own, and least of all on final.

Drag is what buys the descent. You are not diving, you are dragging — the flightpath steepens while the airspeed stays where you put it.

Forward slip and sideslip

The two use the same controls for different jobs, and the difference is what the airplane's path does. In a forward slip the airplane's direction of motion through the air continues the same as it was before the slip began: the nose swings off to one side, the flightpath does not, and you descend faster. In a sideslip the longitudinal axis stays parallel to the original flightpath and the path itself is moved — that is the wing-low crosswind correction that stops drift and keeps the nose straight in the last seconds of a landing.

Hold on to the words there. A forward slip preserves the direction of motion through the air, which on a windy day is not the same thing as preserving the track over the ground. If there is a crosswind, the air you are slipping through is itself moving, and you still have to fly the airplane back onto the centerline extended. That is why the slip and the crosswind correction get combined: forward slip to kill the extra height, then roll out of it into whatever wing-low correction the day requires.

Flying it

1. Configure for landing, get established on the centerline, and reduce the power. The forward slip is normally flown power off.
2. Lower a wing with aileron. If there is a crosswind, lower the wing into the wind so the slip does not carry you downwind of the centerline.
3. Feed in opposite rudder — up to full deflection for the full effect — until the nose is held off and the airplane is still tracking where you want it to go.
4. Lower the nose to hold your approach speed; the drag is being traded for descent rate, not for speed.
5. Vary bank and rudder together to control how steeply you come down, and stop the slip once you are back on glidepath.
6. Recover by rolling the wings level and releasing the rudder pressure together, smoothly, while resetting pitch for the normal glide.

Release that rudder gradually. Let it snap back and the nose swings into line at once, the drag disappears, and the airplane accelerates just as you are running out of altitude to fix it. Finish early enough that you are wings level, aligned and stable before the roundout — you do not land out of a forward slip.

Check the POH before you plan on slipping with the flaps down, and know what you are reading for. Two things sit behind those notes and placards. One is the tail: with the flaps extended, the disturbed air coming off them can wash over the tail in a slip and show up as a pitch buffet or as an elevator with less to say than you expected. The other is fuel: a prolonged slip with a low quantity on board can uncover a tank outlet and interrupt the flow to the engine. Whether either applies to your airplane, and what limitation goes with it, is a question for your POH and not for a rule of thumb.

The airspeed you cannot trust

The static source is the reason. Flying partly sideways puts the air at the static port at an angle the system was never calibrated for, and in many airplanes the indicated airspeed goes noticeably wrong in a slip as a result. This is the one maneuver where the number in front of you is the least reliable thing in the cockpit. Fly the attitude you know is right, listen to the airflow, feel the controls, and do not chase a reading that disagrees with everything else you are sensing.

That matters because the margin above the stall is the thing you cannot afford to guess at down here. A stall in any uncoordinated condition can roll the airplane rapidly, and a rapid roll on final is what you have no altitude to absorb. The handbooks are most pointed about the skid rather than the slip — bottom rudder with the nose yawed into the turn, which is the classic base-to-final setup and the one that rolls the airplane hard toward the inside wing and on toward autorotation. A slip holds top rudder with the wing down and does not carry that same documented tendency. None of which is a reason to be casual: rudder authority fades as you slow, so keep a real margin above the stall and unload immediately at any indication of one.

Wind, energy and knowing when to quit

The slip is an energy tool, so anything that changes your energy changes the slip. A tailwind on final stretches the glide and often sets up the overshoot in the first place. Wind shear can take the bottom out of an approach you thought was stable. Wake turbulence from a preceding heavy is a poor thing to meet while cross-controlled.

So set a point at which you stop. If the slip is not putting you where you need to be, if the airplane is not stable, or if you are still fast and high at the height where the slip has to end, go around. Deciding that early costs you five minutes.

Common errors

The one that hurts is letting the airspeed decay — pitch that does not hold the speed, or reacting to a bad airspeed indication instead of the attitude. Carrying power while trying to lose altitude cancels the maneuver, and slipping in the direction the crosswind is already pushing you drifts you off the centerline you were trying to hold.

The rest are matters of finish: timid rudder that never produces a useful slip, wandering glidepath control, leaving the transition to the crosswind correction until the roundout, and touching down off the centerline or with the longitudinal axis not aligned with the runway. Most of those are cured by looking outside.

Sources

The slip definitions, the static-source airspeed caution, the normally power-off entry and the recovery technique are from the FAA Airplane Flying Handbook (FAA-H-8083-3), which is also where the cross-control stall demonstration and the base-to-final skid warning live. The touchdown tolerance is from the Private Pilot ACS. Flap and fuel limitations on slipping are airplane-specific and come from your POH.

Where you meet it next

On the private checkride this is its own task: touch down at a proper pitch attitude within 400 feet beyond your specified point, with no side drift and the longitudinal axis aligned with the centerline. The slip has to buy you a normal landing, not just a fast descent.

The habits transfer straight into the wing-low crosswind landing, where the same cross-controlled inputs are held for a different reason; work out what the day is asking of you with the crosswind calculator before you walk out. The slow-flight and stall lessons are where the margin above the stall stops being a number and starts being something you can feel, and the go-around is the decision this maneuver is always measured against — all of them sit in the ground school index alongside this one.