The Forward Slip, the Flap Placard Nobody Reads Twice, and the Checkride Trap That Finds Every Student Who Configured the Airplane Before Deciding to Slip

The forward slip is one of the most useful tools in a VFR pilot’s toolkit - and one of the most misunderstood. Executed correctly, it steepens your descent without increasing airspeed, giving you precise energy control on final. Used without understanding your aircraft’s specific limitations, it can put you in a configuration your own POH warns against.

What Is the Difference Between a Forward Slip and a Sideslip?

These terms are not interchangeable, and examiners know when students treat them as if they are.

In a forward slip, the goal is to increase descent rate without gaining airspeed. You put a wing down and apply opposite rudder to yaw the nose sideways. The fuselage presents more surface area to the relative wind, adding drag and steepening the descent. The aircraft continues tracking along the original ground track toward the runway - the nose simply points off to the side.

In a sideslip, the goal is crosswind correction. Wing goes down into the wind, opposite rudder keeps the nose aligned with the runway centerline. Ground track and longitudinal axis are both aimed down the runway. You are managing lateral drift, not vertical path.

Both techniques use crossed controls. The intent, the picture through the windshield, and the application are different. The forward slip is primarily an approach altitude management tool. The sideslip is primarily a crosswind correction tool, most often in the final phase of the landing itself.

On a crosswind approach into a short field, you will often blend them - using the forward slip to get down, then transitioning directly into the sideslip for touchdown. Understand them separately before you combine them.

Why Does Your POH Have a Flap and Slip Restriction?

Open the Pilot’s Operating Handbook for a Cessna 172 Sierra. In the Limitations section, you will find language warning against slips with flaps extended beyond the first detent. Some aircraft have a placard near the flap handle repeating this. It is not fine print. It is a limitation.

There are two documented reasons for this restriction, and your examiner may ask about both.

First: pitch anomaly. With full flaps deployed in certain aircraft, the flaps can disrupt airflow to the horizontal tail. In a steep slip with full flaps, you can get a sudden uncommanded pitch change - sometimes described as a nose tuck. This is documented in flight test programs. The placard exists because it has happened.

Second: airspeed indicator unreliability. The pitot tube measures ram air pressure from the direction of flight. When the aircraft is yawed sideways through the air, the pitot tube is no longer pointed directly into the relative wind. Depending on the angle of the slip and pitot tube placement, the indicated airspeed can read meaningfully higher or lower than actual speed. The instrument is simply inaccurate in that configuration.

This second point has a direct implication for technique: in a forward slip, you must fly by outside reference and by feel, not by the airspeed indicator. You need to know what your aircraft sounds like and feels like at approach speed before you add the complexity of a cross-controlled configuration with an unreliable instrument.

How Do I Execute a Forward Slip Correctly?

You are on final, high, and you have determined a slip is the appropriate tool. Here is the technique, step by step.

Pick a wing. On a calm day, either works. If any crosswind is present, put the upwind wing down as you establish the slip.

Lower the aileron and establish the bank. As the bank develops, apply opposite rudder - enough to prevent a turn and yaw the nose away from the direction of bank. The aircraft is now banked but continuing on the same ground track.

Increase the slip as needed. More bank, more opposite rudder. Hold your aim point on the runway and adjust the intensity of the slip to manage the glide path. The slip provides the drag. Pitch controls the aim point.

Exit cleanly before the flare. Relax the crossed control inputs together and let the aircraft return to coordinated flight, then establish the normal flare attitude. If there is a crosswind, transition directly from the forward slip into the sideslip for touchdown and rollout.

If your airspeed is increasing during a forward slip, you do not have a proper forward slip. What you have is a nose-low approach with crossed controls. Add back pressure, re-establish the yaw, and then manage pitch to hold the approach angle.

What Is the Order-of-Operations Trap on Checkrides?

This is the mistake that catches prepared students who learned the maneuver without learning the why.

A student configures the aircraft for landing first - full flaps, airspeed stabilized, everything looking good. Then they realize they are high. They reach for the forward slip.

If the aircraft has a flap restriction in the POH, they have just placed themselves in a configuration the manufacturer warns against. The order of operations matters: plan the slip before going to full flaps, not after.

The correct answer when you are high on final in a Cessna 172 with that restriction and already at full flaps is to go around. Know that before you need to know it.

Aircraft vary. The Piper Cherokee has no flap and slip restriction. The Cessna 172 with certain flap configurations does. Some older taildraggers have no restriction and use the slip as a primary approach tool. Know the specific limitations for the airplane on your checkride.

What Does the ACS Require for Forward Slips?

The Airman Certification Standards (ACS) for the private pilot certificate list forward slips as a task under Area of Operation Eight: Approaches and Landings. The standard requires that you plan and follow a flight path to the selected landing area, consider obstacles, maintain appropriate approach speed with drift and ground track controlled, and touch down within 400 feet beyond your selected aim point.

Examiners are looking for four specific things:

1. Recognition - that you correctly identified the situation, understood you were high, and assessed that conditions permitted a slip given your aircraft’s limitations.
2. Execution - deliberate entry, aileron down, opposite rudder, managing both inputs together.
3. Knowledge of limitations - the placard, the airspeed indicator unreliability, the pitch anomaly with full flaps if applicable.
4. Accuracy - landing in the target zone. If you used the slip and still landed long, you used the tool but did not accomplish the goal.

What Are the Most Common Forward Slip Mistakes?

The most frequent error is letting the nose drop too aggressively while applying rudder, which causes airspeed to increase. The result looks similar from outside - steep, fast approach - but the control inputs are wrong and the transition to the flare is messier than it should be. A proper forward slip holds pitch to maintain the approach angle while the slip geometry provides the drag.

The second common error is attempting the slip too late. At 200 feet above the threshold while still significantly high, a slip will likely not solve the energy problem in the remaining time and altitude. Go around.

When Should You Use a Forward Slip in an Engine-Out Emergency?

The forward slip is a core technique for engine-out emergency approaches. With a field selected and the aircraft configured, you have two modes for managing the glide: reduce drag to extend the glide (clean configuration, best glide speed) or increase drag to steepen it (forward slip). Transitioning fluidly between those two modes is part of emergency procedure training and is covered in the ACS.

If you have only ever practiced slips on normal approaches with power available, that gap is worth dedicated work. The power-off slip on short final - managing energy without a go-around option - carries higher mental overhead and a lower margin for technique errors.

When Should You NOT Use a Forward Slip?

Several conditions argue against using a forward slip:

Moderate or severe turbulence. An intentionally cross-controlled configuration increases upset potential when gusty conditions are already demanding attention.

Insufficient altitude on short final. You need enough altitude to establish the slip, manage the descent, and exit cleanly before the flare.

Gusty, variable crosswinds. Adding intentional cross-controls to an already high-workload environment compounds the difficulty.

Aircraft at full flaps with a POH restriction. As covered above - go around.

The go-around is always the correct answer to an approach that is not working. Examiners are not testing whether you can save every bad approach. They are testing whether you recognize when saving it is not the right call.

Key Takeaways

• A forward slip and a sideslip both use crossed controls but serve different purposes: the forward slip manages altitude on final, the sideslip corrects for crosswind. Know the distinction before your oral.
• The Cessna 172 Sierra POH contains a limitation against slipping with flaps extended beyond the first detent, due to documented pitch anomalies and airspeed indicator unreliability in a slip.
• Plan the slip before going to full flaps - not after. Reconfiguring to full flaps and then attempting a slip in a restricted aircraft is the most common checkride trap in this area.
• In a forward slip, fly by feel and outside reference. The airspeed indicator is unreliable when the pitot tube is yawed out of the relative wind.
• The ACS requires touchdown within 400 feet of the aim point for forward slip tasks. Using the technique and still landing long means the goal was not accomplished.