Slow Flight After the ACS Rewrite, the Stall Warning You Cannot Trigger, and the Checkride Standard Most Students Are Getting Wrong

The current Airman Certification Standards (ACS) require slow flight to be performed without activating the stall warning system - a significant departure from the older Practical Test Standards. Many students are training to the wrong standard and discovering the gap only when a designated pilot examiner closes the book.

What Changed Between the PTS and the ACS?

Under the old Practical Test Standards (PTS), slow flight was demonstrated at minimum controllable airspeed (MCA) - right at the edge of a stall, with the stall warning active and controls mushy. The goal was to show mastery in a degraded state, and that reasoning was not wrong.

The ACS changed the method, not the goal. The examiner now expects the applicant to establish and maintain slow flight without activating the stall warning. Not right at the edge. Above it. That single phrase changes everything about how the maneuver is set up and flown.

Why Does Slow Flight Exist as a Checkride Task?

The FAA wants to confirm that a pilot can fly with precision at low airspeed and high angle of attack - the conditions present on final approach, during a go-around, or any moment when the airplane is slow and margin is thin.

The competency being tested is not dancing at the edge of a stall. It is flying precisely in a slow regime, recognizing any degradation in performance, and keeping the airplane exactly where the pilot put it. Under the ACS, the stall warning signals that a boundary has been crossed that should not have been crossed.

Some designated pilot examiners will mark a single chirp of the stall horn as an unsatisfactory performance. Not because the airplane was out of control, but because the ACS says no stall warning - and the warning went off. Train to the standard.

What Are the ACS Tolerances for Slow Flight?

The ACS specifies four tolerances that must all be held simultaneously:

• ±100 feet of the specified altitude
• ±10 degrees of the specified heading
• Bank angle not to exceed 5 degrees during straight and level slow flight
• Specified airspeed maintained without triggering the stall warning

Holding all of these at a high angle of attack, in thermals or light turbulence, takes deliberate practice. The no-stall-warning requirement is non-negotiable underneath all of them.

How to Set Up the Transition into Slow Flight

Clear the area first. Two 90-degree clearing turns - not a formality, but an active scan before any slow flight task.

Reduce power smoothly. In most Cessna 172s, the initial power reduction begins around 1,500–1,600 RPM. As speed decreases, raise the nose to maintain altitude. The transition is active, not passive - the pilot is continuously adjusting pitch and power as the speed decays.

Do not reduce power and wait. That is the first place the maneuver is lost. The airplane will find the stall warning on its own if left unmanaged.

How to Use Flaps and Trim During Slow Flight

Extend flaps in increments. Each increment changes both the pitch and power requirement. When flaps extend, the nose pitches down - add back pressure. When drag increases, a small power addition holds altitude. Each flap change requires a trim adjustment.

Trim is the most underused tool in slow flight. Flying at high angle of attack means carrying sustained back pressure on the yoke. Holding that by hand for several minutes while turning and reconfiguring introduces fatigue, and fatigue introduces errors. Trim the aircraft, remove the hand pressure, and let the trim tab do the work so inputs remain precise.

How to Find Your Airplane’s Stall Warning Threshold

Before a checkride, know the specific indicated airspeed at which the stall warning activates in each configuration in that specific airplane - not a rough estimate, but the actual number.

The exercise: establish level flight in clean configuration, slow gradually, and note the airspeed when the stall warning first sounds. Repeat with 10 degrees of flaps, then with full landing flaps. Write down each number.

If the stall warning activates at 56 knots in landing configuration, the target slow flight airspeed is 60–61 knots - a 4–5 knot buffer. That is the working airspeed. Flying with a specific number rather than a feeling is the difference between managing the maneuver and reacting to it.

How to Execute Coordinated Turns in Slow Flight

At high angle of attack, adverse yaw is amplified. Rudder inputs must match aileron inputs precisely. A sloppy turn produces a ball slide, a nose drop, altitude loss, and possibly a stall warning - one uncoordinated input cascades into three corrections.

The technique is the same as any coordinated turn, but the demands are higher. Lead with rudder on entry, step on the ball throughout, and maintain coordination through the rollout. Bank angle stays around 15 degrees - shallow, smooth, and controlled.

One additional input: rolling into a bank decreases effective lift. At slow flight airspeeds, already close to the stall warning threshold, any lift decrease deserves attention. Add a small amount of back pressure entering the bank and release it rolling out. Practice until that input is automatic.

How to Recover from Slow Flight

The ACS recovery sequence is specific:

1. Simultaneously add full power and reduce angle of attack
2. Keep wings level
3. Let airspeed build
4. Retract flaps in increments as airspeed increases to a safe value for each increment
5. Return to the specified heading, altitude, and airspeed

The most common recovery failure is pulling flaps up all at once. A large flap retraction at low airspeed drops lift suddenly, the nose pitches, the airplane sinks, back pressure goes in, and the pilot is right back near the stall warning on the way out of the maneuver.

Retract incrementally. Verify airspeed before each move. Those extra seconds are exactly what a disciplined recovery looks like to an examiner.

Why This Standard Matters Beyond the Checkride

The ACS change has direct safety implications. The departure stall - particularly from an overshoot on the final approach turn - often follows a sequence where the stall warning has been active for some time and the pilot has been conditioned to treat it as background noise.

The old standard normalized operating with the horn on. The ACS treats the stall warning as a hard limit, not a regime to operate within. If that boundary is trained deeply enough, any activation of the stall warning on any flight triggers an immediate unload of the wing. That is the instinct the new standard is designed to build - and it is a better mental model than the one it replaced.

Slow Flight Checkride Preparation Checklist

• Confirm where the stall warning activates in each flap configuration in your specific airplane
• Practice the transition as a deliberate sequence: power, pitch, trim, flaps - actively managed from first power reduction through established slow flight
• Identify your margin: find the horn threshold, fly 5 knots above it, hold it with precision
• Practice turns specifically - coordination failures appear in the turns, not straight-and-level
• Practice incremental flap retraction on the recovery until the sequence is automatic

Key Takeaways

• The ACS requires slow flight with no stall warning activation - a direct change from the older PTS standard that required flight at minimum controllable airspeed
• A single chirp of the stall horn is sufficient for an unsatisfactory mark from many examiners
• ACS tolerances are ±100 feet altitude, ±10 degrees heading, bank not to exceed 5 degrees
• Know the specific airspeed at which the stall warning activates in your airplane in each flap configuration - fly 4–5 knots above that threshold
• Trim, coordination, and incremental flap management are the three most common points of failure