Slow Flight and the ACS Rewrite: Why the Maneuver Changed and What Examiners Are Actually Looking For Now

The 2017 update to the FAA’s Airman Certification Standards (ACS) quietly redefined slow flight. What was once a maneuver that required a continuously blaring stall horn is now about operating right at the edge of a stall warning - close enough that any small input would trigger it, but not past the threshold. If your instruction predates that change, you may be practicing a maneuver that no longer matches what examiners expect.

What Changed About Slow Flight in 2017?

Before the ACS replaced the Practical Test Standards, slow flight was taught as flight at minimum controllable airspeed. The goal was to slow the airplane until the stall horn activated and stayed on - continuously. Full flaps, low power, nose high, horn blaring. Instructors called it “dirty and slow.”

That approach had a problem. Flying with the stall horn continuously active means you are past the first indication of an impending stall and holding that position on purpose. That is not a controlled, teachable skill - it is a hazard being practiced repeatedly.

The 2017 ACS changed the definition to address exactly that.

How Is Slow Flight Defined Under the ACS?

The current ACS defines slow flight as operating at an airspeed at which any further increase in angle of attack, any increase in load factor, or any reduction in power would result in a stall warning.

Each part of that definition matters:

• Any further increase in angle of attack - a slight pitch-up would trigger the warning
• Any increase in load factor - rolling into a bank would trigger it
• Any reduction in power - pulling the throttle back would trigger it

The critical phrase is “would result in a stall warning” - not “has already resulted.” The ACS wants you flying right at the edge of the warning system without crossing over it. That is a fundamentally different task than what many pilots trained on.

How Do I Set Up Slow Flight Correctly?

Begin the maneuver at least 1,500 feet AGL, and preferably more. Clearing turns come first - two 90-degree turns in opposite directions, or one 180-degree turn. Confirm traffic and terrain before slowing down.

The setup sequence:

1. Reduce power smoothly
2. Apply carb heat if required, or fuel pump if the airplane calls for it
3. As airspeed decreases into the flap operating range, extend flaps in increments - typically 10°, then 20°, then full
4. Pitch up to maintain altitude as the airplane slows
5. Add power back to compensate for the drag the flaps create
6. Trim continuously as pitch and power change throughout the setup

Extending full flaps all at once while still at speed causes a pitch change you do not want in a slow-flight setup. Staged extension keeps the airplane manageable.

What Am I Looking for at the Edge of the Envelope?

You are pitching for airspeed and using power to hold altitude. The nose is high. The controls feel heavy and sluggish. The stall horn may flicker or give a brief chirp.

That chirp is correct. Continuous horn is not.

Most training airplane stall warning systems activate somewhere between 5 and 10 percent above the actual stall speed. The ACS asks you to operate in that band - above the stall, within range of the warning, but not triggering it on your own. A gust, a bank, or a power reduction should push you over that line. Your control inputs should not.

If the horn is blaring continuously, you have gone past the threshold. A small addition of power, or a slight relaxation of back pressure, will bring you back into the correct window.

How Do I Handle Turns in Slow Flight?

Turns are where checkrides go sideways. When you roll into a bank at slow flight speeds, two things happen simultaneously:

• Load factor increases, which raises the stall speed
• The nose can drop slightly as you establish the bank, reducing airspeed further

Both push you closer to a stall. Counter this with immediate, coordinated back pressure as you roll in, and a smooth return to the trimmed pitch attitude as you roll out.

Bank angle matters. The ACS typically expects no more than 30 degrees of bank, and most designated pilot examiners are comfortable with 20 degrees or less during this task. The margin between controlled flight and an accelerated stall narrows sharply past 20 to 25 degrees at these speeds.

Adverse yaw is amplified in slow, high-angle-of-attack flight. The drag differential across the ailerons is significant. Without active rudder input, a left bank can become a crossed-control setup - nose yawing right, left wing dropping further than intended. Keep the ball centered throughout every turn.

What Are the ACS Tolerances for Slow Flight?

The private pilot ACS specifies these tolerances for slow flight:

• Airspeed: ±10 knots of the target
• Altitude: ±100 feet of the assigned altitude
• Heading: ±10 degrees
• Bank angle in turns: within 5 degrees of the assigned bank

The numbers are more generous than some tasks. But tolerances matter less than concept. An examiner watching a pilot hold steady airspeed with the horn blaring the entire time knows immediately that the maneuver was trained incorrectly. The numbers only mean something if the pilot demonstrates an understanding of where the edge actually is.

Know your airplane’s Vso - the stall speed in the landing configuration with power idle. The ACS does not specify a target airspeed because every airplane is different. Work out a target with your instructor that puts you right in the warning band above Vso.

How Do I Recover from Slow Flight Correctly?

Recovery is part of the evaluation. A rushed or sloppy return to cruise tells the examiner you were waiting for the maneuver to end.

The correct sequence:

1. Add power smoothly
2. Pitch for the cruise attitude
3. Retract flaps in stages as airspeed builds
4. Manage back pressure throughout - each flap increment changes the pitch trim requirement
5. Trim again as speed and configuration change

A smooth, coordinated recovery that mirrors the deliberate setup demonstrates that you understood what you were doing from start to finish.

Why Does Slow Flight Mastery Actually Matter?

The maneuver exists because the edge of the envelope appears in real operations, not just practice areas.

Consider a stabilized approach to a short field - one-mile final, full flaps, airspeed at 1.3 times Vso. A gust pitches the nose up slightly. You lose half a knot. The stall horn gives one brief chirp.

That chirp is slow flight, in real life, close to the ground. A pilot who has spent real time at the edge recognizes it immediately - adds a touch of power, slightly lowers the nose, reestablishes approach speed. A pilot who learned only the rote maneuver may not recognize what just happened, or may instinctively pull back because the ground is close.

The ACS changed the definition because flying with the horn blaring was a training behavior, not a survival skill. Time spent living in the warning band - making small adjustments, feeling the controls, listening to what the airplane communicates - builds the instinct that matters when conditions deteriorate on final.

Slow flight is found in Area of Operation Four of the private pilot ACS. The reference material is the Airplane Flying Handbook and the Airman Certification Standards, both available free at faa.gov.

Key Takeaways

• The 2017 ACS redefined slow flight from sustained stall horn activation to flying at the edge of the warning system without triggering it continuously
• The correct standard: any increase in AOA, load factor, or reduction in power would result in a stall warning - the warning is not already active
• Setup requires pitched-for-airspeed, power-for-altitude technique with flaps extended in stages and continuous trim input
• Turns require immediate back pressure, shallow banks (20–30 degrees maximum), and active rudder throughout to counter adverse yaw
• The real value of this maneuver is the feel it builds - recognizing the edge on short final is when it actually saves you