Slow Flight, the 2016 ACS Rewrite, and the Maneuver You Now Fly With the Stall Horn Silent

Slow flight changed in June 2016, and many pilots are still flying it the old way. Under the FAA’s Airman Certification Standards (ACS), you now fly at an airspeed just above the stall warning - not with the horn blaring the whole time. The target is the slowest speed at which any further increase in angle of attack, increase in load factor, or reduction in power would trigger the stall warning. Fly to the edge of the warning, not into it.

What Changed About Slow Flight in 2016?

For decades, slow flight was taught as flight at minimum controllable airspeed. You slowed the airplane to the ragged edge and flew around - holding altitude, making turns - with the stall warning horn sounding the entire time. We believed that taught students to control the airplane on the verge of a stall.

The problem, which took the FAA and a lot of accident data to name, was this: we were training pilots to ignore the stall warning. After minutes of flying with the horn as background noise, the horn stopped meaning danger. It became the soundtrack to a maneuver.

Then those same pilots would turn base to final a little slow and a little uncoordinated, the horn would sound, and some part of their brain filed it as “just the slow flight noise” - and they’d keep pulling. Loss of control in flight has sat at or near the top of the general aviation fatal accident list for years, and much of it happens in the pattern, low and slow, exactly where a stall horn should be the loudest, most unignorable alarm in your life.

So in June 2016, when the FAA replaced the old Practical Test Standards (PTS) with the Airman Certification Standards (ACS), it changed slow flight on purpose. The FAA reinforced the change that September 2016 with a Safety Alert for Operators (SAFO) on maneuvering during slow flight, spelling out the reasoning: break the habit, and make the stall warning mean something again. The correct response to that horn is to reduce the angle of attack - every single time.

One clarification worth noting: the FAA later confirmed that an instructor may still demonstrate deeper slow flight in training, down into the buffet, as long as it’s intentional and briefed. Training and testing are not the same thing. But on the checkride, the target is clear - slow, stable, coordinated, and no horn.

How Do I Fly Slow Flight to ACS Standard?

Start with clearing turns. The examiner is looking for them, and you’re about to spend a couple of minutes nose-high and slow - a poor time to discover traffic beneath you. Clear the area and pick a reference.

Enter with a power reduction. Add carb heat if your airplane needs it, pull the power back, and raise the nose to hold altitude as the airplane slows. The controls go mushy, the nose sits high, and you’ll see a lot of cowling and little horizon.

Add power back in as you approach target speed. On the back side of the drag curve, it takes power to fly slow and hold altitude. This is the counterintuitive heart of the maneuver: power controls altitude, pitch controls airspeed. If you’re low, add power - don’t pull. If you’re fast, raise the nose - don’t chop the throttle.

Trim it. This is the single biggest favor you can do yourself. A trimmed airplane in slow flight nearly flies itself while you manage small corrections; an untrimmed one wears you out and magnifies every wobble.

Feed in right rudder - a lot of it. High power and low airspeed means engine, propeller, and slipstream effects are all trying to yaw you left. An uncoordinated airplane at high angle of attack is the exact setup for a wing dropping. Keep the ball centered with your feet.

What Are the ACS Tolerances for Slow Flight?

For the private pilot ACS, hold:

• Altitude: within ±100 feet
• Heading: within ±10 degrees in straight flight
• Bank: within ±10 degrees in turns
• Airspeed: +10 knots / −0 knots

That minus-zero matters. The examiner will allow ten knots fast but will not allow any slow, because slow is toward the stall. Underneath the numbers, the examiner wants to see that you’re comfortable - that you can fly at a speed most pilots never touch, hold it steady, make a turn, and roll out cleanly while respecting the edge without fearing it.

What Are the Most Common Slow Flight Mistakes?

1. Chasing. You get low, pull the nose up, slow further, sink more, pull more - and now the horn’s going off and the airplane is getting away from you. Flip it: low means add power, fast means raise the nose. Use small inputs and wait for the airplane to answer.

2. Forgetting the power. Pilots pull the throttle to enter and leave it there, then wonder why they can’t hold altitude. Slow flight is a high-power maneuver. Keep a hand on the throttle the whole time.

3. Letting the horn blare. If your instructor learned this maneuver before 2016 and taught it the way they learned it, you may be flying it too deep. On today’s checkride, a horn that sounds and stays on is a fault. Learn where that speed is in your airplane and park it just above the warning.

4. Feet asleep. The ball sits out to one side and the applicant never touches the rudder. Coordination here is a safety item, not an option. Right rudder - keep it centered.

5. Fixating. Locking onto the airspeed needle while heading drifts, altitude slips, and traffic goes unnoticed. Slow flight is a scan: airspeed, altitude, heading, attitude out the window, and the ball. Keep the eyes moving.

6. Rushing the recovery. The recovery is a maneuver too, and the examiner is watching. Add full power smoothly, reduce the angle of attack to build speed, manage right rudder as power comes in, retract flaps on your airplane’s schedule, and climb or hold altitude cleanly. Don’t shove everything forward and balloon, and don’t let the nose drop.

Why Does Slow Flight Actually Matter?

Slow flight isn’t a party trick or a box to check - it’s the pattern. Every base-to-final turn is slow flight. Every short-field landing and every soft-field takeoff held just off the runway in ground effect is this maneuver. Learning to feel an airplane at low speed, high angle of attack, high power, coordinated and calm, builds the exact instincts that keep pilots alive in the pattern - for the gusty base-to-final turn two years from now when you’re tired and want to be home.

Your homework: next time up with an instructor or safety pilot, climb to at least 1,500 feet above the ground (more is better), clear the area, and live in slow flight for a while. Get it trimmed. Feel where the stall-warning edge is. Make turns both directions and notice how much the airplane wants to overbank and how much rudder it takes to stay coordinated. Get comfortable being uncomfortable, then fly a clean recovery - and do it again. A few rounds of that, and the checkride version stops being scary.

Key Takeaways

• The 2016 ACS changed the target: fly at the slowest speed just before the stall warning activates, not with the horn sounding.
• The change exists to fight loss-of-control accidents by making the stall warning meaningful again - the correct response to the horn is always to reduce angle of attack.
• Power controls altitude, pitch controls airspeed on the back side of the drag curve; trim the airplane and feed in right rudder.
• Private pilot ACS tolerances: altitude ±100 ft, heading ±10°, bank ±10°, airspeed +10/−0 knots.
• Slow flight is the pattern - mastering it builds the instincts that protect you in the base-to-final turn.