Slow Flight, the ACS Standard Every Student Gets Wrong, and the Stall Warning That Should Stay Off

The 2017 Airman Certification Standards (ACS) changed how slow flight is evaluated on the private pilot checkride, and the change never got the attention it deserved. The current standard requires flight “at an airspeed above the onset of the stall warning” - not at it, not through it. If you demonstrate slow flight with the horn blaring continuously, you can be marked unsatisfactory by an examiner following the current document.

This is one of the most commonly misapplied tasks on the checkride, and it costs students who have otherwise prepared thoroughly.

What Does the ACS Actually Require for Slow Flight?

The governing document is the FAA Private Pilot Airman Certification Standards, Area of Operation VII, Task A. The specific language calls for maintaining flight at an airspeed “above the onset of the stall warning.” That phrase replaced the older Practical Test Standards interpretation that many instructors, textbooks, and prep guides carried forward - the one that treated a sounding horn as the target, not a boundary to stay above.

The old standard encouraged students to find the horn and hold it. The current standard requires something more demanding: the ability to fly deliberately in the regime just above that edge, using feel and instrument scan rather than an auditory alarm as the primary reference.

Why the FAA Changed the Standard in 2017

The change reflects how general aviation accidents actually happen. More GA accidents occur in the traffic pattern than in any other phase of flight. A significant portion involve loss of control at low altitude and low airspeed - pilots slow on final, pilots stretching a glide, pilots allowing the nose to drop through the base-to-final turn while already behind the power curve.

The physics explanation is what makes the standard change logical. At low airspeed, aircraft enter what is sometimes called the region of reverse command. In this regime, drag increases faster than lift is generated. More power is required just to hold altitude. Control response slows noticeably. Aileron authority drops. This region begins well before the stall warning horn ever sounds.

Flying slow flight to the horn means flying right at the edge of that region, close to the break. The ACS is asking pilots to demonstrate comfortable, deliberate management of the aircraft within that region - not brinksmanship at its boundary.

What Airspeed Should You Target?

On most light training aircraft, target an airspeed five to ten knots above the published stall speed for your configuration. In a Cessna 172 with full flaps, the stall speed is approximately 40 knots. A reasonable target is 45 to 50 knots indicated, adjusted for weight and density altitude. The nose will be noticeably high. The controls will feel different. The horn should be quiet.

That quiet horn is not an absence of slow flight. It is correct slow flight under the current ACS standard.

How to Set Up the Maneuver Correctly

Clear the area first. Two 90-degree clearing turns, or one 180-degree turn. This is not optional. At high nose attitudes, forward visibility is reduced. The examiner will be watching for it as a demonstration that collision avoidance is part of your standard decision-making.

Coordinate the entry. Reduce power and raise the nose simultaneously to hold altitude while airspeed bleeds off. The common mistake is to reduce power, wait, watch the speed fall, then pull - that sequence costs altitude. Power back and nose up together, so the energy converts without altitude loss.

Add flaps per the examiner’s instructions. Listen carefully to the brief. If the configuration is not specified, ask before beginning.

Why Trim Is the Most Overlooked Step

At a high nose attitude in slow flight, significant back pressure is required to hold altitude. Most students grip the yoke and hold that pressure manually for the entire demonstration. Experienced examiners recognize this immediately, and it works against you for two reasons.

First, altitude control suffers. Fighting constant back pressure causes the altitude to wander. Trim removes that fight so small corrections are possible instead of constant compensation.

Second, your scan collapses. In slow flight, you need to be moving your eyes: altitude, heading, airspeed, traffic, outside reference. If full attention is going to the yoke, the scan falls apart and heading slowly drifts. Run the trim wheel until the aircraft holds its own at the target airspeed with minimal hand pressure.

How to Manage Power in Slow Flight

Slow flight is not idle power. The aircraft needs energy to maintain altitude at a high angle of attack in an elevated-drag regime. Know roughly what power setting holds altitude in your slow flight configuration for your aircraft - it varies by weight and density altitude. Set it, trim, and then manage small corrections. Students who don’t explore this in training spend the checkride chasing altitude with large, continuous power changes.

The ACS tolerances are: ±10 knots airspeed, ±100 feet altitude, ±10 degrees heading. These are achievable - but they require a trimmed, properly configured aircraft and an active scan.

How to Handle Turns in Slow Flight

Turns are where the checkride separates students who understand the maneuver from those who have only ever flown it in a straight line.

At slow airspeed, aileron deflection creates significant adverse yaw. The down-going aileron generates drag. Without active rudder input, the nose yaws opposite to the direction of turn. In a left turn, the nose swings right. The result is a skidding turn with the ball displaced to the outside.

A skidding turn at slow speed and high angle of attack is the setup for a cross-controlled stall. At low altitude, that is a serious accident scenario. The examiner is watching the inclinometer.

Use more rudder than feels normal. Step on the ball and keep it centered throughout the turn. As you enter the bank, add power to compensate for increased induced drag. Typical bank angle is 20 to 30 degrees - even at 20 degrees, the aircraft will want to descend without power compensation. Roll out coordinated, with opposite aileron and opposite rudder applied together to prevent the nose from swinging on rollout.

How to Execute a Clean Recovery

The transition back to cruise is part of the evaluated demonstration even when it isn’t listed as a separate task. Add power smoothly, lower the nose to a cruise attitude, retract flaps in sequence per the AFM or POH, and manage the airspeed as the aircraft accelerates. Don’t pitch down abruptly. Don’t let altitude balloon from being slow to lower the nose. The recovery is watched.

Why This Matters Beyond the Checkride

Consider a real scenario: an unfamiliar airport, a shorter runway than planned, a forward slip on final that works but bleeds the airspeed more than expected. The threshold is approaching and the speed is low. Do you know where you are in the envelope?

A pilot trained to the horn as the reference may not - because the horn is the signal to act, meaning the margin was already gone before awareness arrived. A pilot trained to fly above the onset knows what heavy controls feel like, knows what the rudder working harder means, knows whether there is still margin before any warning activates. That awareness is what the ACS is designed to build: a pilot who understands the energy state of the aircraft through feel and instrument scan, not one who has learned to make a horn sound.

Key Takeaways

• The 2017 ACS changed the slow flight standard: the stall warning horn must remain off, not on, during correct execution.
• The ACS language - “above the onset of the stall warning” - is specific and enforceable. Flying with the horn sounding can result in an unsatisfactory grade.
• In a Cessna 172 with full flaps, target approximately 45–50 knots - above the ~40-knot stall speed for that configuration.
• Trim is essential. An untrimmed aircraft makes it nearly impossible to hold altitude tolerance (±100 feet) for more than a few seconds.
• Turns require active rudder use. Adverse yaw at slow speed, combined with a skid, creates a cross-controlled stall scenario the examiner is specifically watching for.
• The goal of slow flight training is pilot awareness in the region of reverse command - not the ability to hold a horn at threshold.