Slow Flight, the ACS Change That Dropped the Stall Warning, and the Checkride Trap Hiding in a Maneuver Most Students Think They Have Already Mastered

The 2017 update to the FAA’s Airman Certification Standards (ACS) quietly changed what examiners expect from slow flight on the private pilot checkride. The new standard requires slow flight to be performed at an airspeed just above the stall warning activation point - not with the warning blaring. Many training programs never fully absorbed this change, and students continue showing up to checkrides demonstrating the wrong standard.

What Changed About Slow Flight in the 2017 ACS Update?

Under the old Practical Test Standards, minimum controllable airspeed meant exactly that: slow the aircraft until the stall warning horn activates, and fly it there. The goal was an airplane on the edge of the envelope with the warning continuously active.

The ACS revised this. Slow flight is now performed at an airspeed just above stall warning activation - above the warning band, not inside it. This is a meaningful aerodynamic distinction. Flying with the stall warning active means operating within roughly 5 to 10 knots of an actual stall, with almost no energy margin to absorb a gust, a small pitch excursion, or a bank angle addition.

The revised standard tests something more practically useful: can you manage the airplane at the low-speed edge of its envelope, in a controlled and coordinated way, without deliberately sitting in the warning zone?

On checkride day, examiner responses to the old technique vary. Some will accept it, some will note it, and some will mark it against you. The ACS is the scoring guide. Train to it.

How Do You Set Up Slow Flight Correctly?

Start by clearing the area - not as a formality, but because at slow speeds with flaps deployed, turns are wider and energy management is different. Clear left, right, above, and below.

The entry sequence in a typical training aircraft like the Cessna 172:

1. Reduce power gradually
2. Apply carburetor heat if required
3. Extend flaps incrementally as airspeed drops into the white arc (roughly 40 to 85 knots in the C172)
4. Apply back pressure to hold altitude as pitch attitude rises
5. Adjust trim to reduce control pressure

As you slow down, the pitch attitude will be noticeably higher than cruise. In a C172, the nose-high attitude can feel uncomfortable the first several times. The controls will feel mushy - this is expected. At slow flight speeds, control surfaces are less effective because there is less airflow over them. More input is required to get a response, and more anticipation is required to stay coordinated.

Your target speed should be just above where the stall warning activates. The stall warning typically triggers 5 to 10 knots above the actual stall speed depending on the aircraft. In the Cessna 172S, the power-off stall speed in the landing configuration is approximately 44 knots calibrated airspeed. With power on, that number drops slightly because thrust contributes to lift. Know your aircraft’s numbers from the POH before the checkride.

Why Is Coordination So Critical at Slow Flight Speeds?

Uncoordinated flight at low airspeed is dangerous in a way it simply is not at cruise. A skidding turn in slow flight with full flaps is a direct setup for an accelerated stall.

The examiner is watching your ball throughout the entire maneuver. If you apply rudder without aileron, or aileron without rudder, you can rapidly develop a slip or skid that makes a stall significantly more likely and more dangerous.

The objective is coordinated flight from entry through recovery: shallow bank angles, smooth inputs, rudder working with the ailerons. Slow flight isn’t a test of how slow you can fly - it’s a test of how well you manage the airplane when normal aerodynamic feel is gone and energy margins are thin.

What Are the ACS Tolerances for Slow Flight?

The ACS performance standards for slow flight are:

• Altitude: ±100 feet
• Heading: ±10 degrees
• Airspeed: ±10 knots of the target speed
• Bank angle in turns: not to exceed 30 degrees

These tolerances are achievable in calm conditions. They become genuinely challenging in light chop, because the airplane has no energy margin to absorb perturbations. Students who have only practiced slow flight in smooth air frequently discover this on checkride day. The fix is deliberate practice in a range of conditions.

How Do You Fly Turns in Slow Flight?

This is where most students underperform. Many practice the entry and straight-and-level portion but neglect the turns - and that is where the maneuver reveals what you actually know.

When you roll into a bank in slow flight, the inside wing is moving slower than the outside wing. The inside wing is therefore operating closer to its stall speed. Without coordinated rudder input, that inside wing will want to drop further, and an accelerated stall can develop quickly.

Technique for turns in slow flight:

1. Lead with rudder - more input than you would use at cruise
2. Establish a shallow bank, typically not more than 20 to 25 degrees
3. Hold pitch attitude steady to maintain altitude
4. Anticipate the rollout by beginning to level the wings a few degrees before the target heading - the airplane is responding slowly and will continue turning slightly after you neutralize the controls

If the examiner asks for a turn to a specific heading, apply coordinated aileron and rudder, hold pitch, and roll out precisely on the heading. The whole maneuver should look like deliberate aircraft control.

How Do You Recover From Slow Flight Without Stalling?

The recovery is part of the maneuver, and rushing it is one of the most common checkride mistakes.

Correct recovery sequence:

1. Smoothly apply full power
2. As power comes in, relax back pressure - the nose will want to pitch up with full power; resist this
3. Retract flaps in stages as airspeed builds into the appropriate range for each configuration
4. Maintain altitude throughout the acceleration back to cruise speed

Do not retract flaps to zero while still at slow flight speed. The flaps are contributing to lift. Remove them too early and the airplane will sink. The correct stage speeds for flap retraction are in the POH - know them before the checkride.

The ACS requires recovery without exceeding pitch and bank tolerances and without entering a stall. Pitching the nose up steeply while retracting flaps can stall the airplane during the recovery from slow flight. This is a checkride-ending event.

What Should Your Instrument Scan Look Like in Slow Flight?

Even in visual meteorological conditions, instrument scan discipline is required. The pitch attitude in slow flight is high enough that students sometimes let the nose creep progressively higher because each increment begins to feel normal.

Watch specifically:

• Airspeed indicator: If the needle is creeping downward, the nose is too high. Add power - do not pull back further.
• Altimeter: If altitude is unwinding while airspeed drops, power is the correction, not pitch.
• VSI and ball: Cross-check continuously for uncoordinated flight or developing sink rates

The correct response to sinking in slow flight is to add power and hold the pitch attitude. The instinct to pull back is wrong - it reduces airspeed without arresting the sink and moves you toward a stall.

What Configuration Does the ACS Require for Slow Flight?

The ACS specifies the landing configuration, which for most training aircraft means full flaps. However, an examiner may ask for slow flight in a different configuration - approach flaps, or clean. Each configuration produces a different stall speed and a different slow flight target airspeed, and the airplane handles noticeably differently in each.

Before the flight, brief the stall speeds for each configuration in your aircraft. They are in the POH. Know the numbers cold.

How Should You Practice to Be Checkride Ready?

The students who perform slow flight well on checkride day are the ones who practiced it until it felt routine - until the instrument scan was automatic, the coordination was natural, and the tolerances felt wide.

Before your checkride:

• Pull up the FAA’s private pilot ACS (a free document on the FAA website)
• Navigate to Area of Operation VI, Task B: Slow Flight
• Read the task description and performance standards exactly as written
• Practice specifically to that standard - the examiner is using it as a scoring guide

If asked to explain why the standard changed, the answer is straightforward: flying with the stall warning continuously active is not a technique used in real operations, and the revised standard tests a more practically transferable skill.

Key Takeaways

• The 2017 ACS update changed slow flight from “fly with the stall warning active” to “fly just above stall warning activation” - many students are still training to the old standard
• Coordination is the examiner’s primary focus in slow flight; a skidding turn with full flaps at low airspeed can produce an accelerated stall
• Power corrects altitude loss in slow flight, not pitch - adding back pressure when sinking is the wrong response
• Turns are where the maneuver is won or lost; practice them far more than straight-and-level slow flight
• Recovery is part of the maneuver - retract flaps in stages, never all at once, and use the POH speeds for each configuration stage
• The ACS is free and public; read the actual task description before your checkride, not a summary of it