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Slow going

Taming the stall’s hairy edge

Your first few hours as a student pilot give you a taste of some of the basic maneuvers that you’ll use every time you fly—takeoffs, climbs, turns, descents, and landings.

Illustration by Jan Feindt
Illustration by Jan Feindt

Then comes the lesson where you’ll be introduced to slow flight—sometimes called “minimum controllable airspeed”—a maneuver designed to familiarize you with an airplane’s behavior when you’re flying at airspeeds very near stall speeds. Competence in flying so slowly is important because it builds an awareness of the airplane’s control feel when airspeed is critically low and a stall may well be imminent.

How do you begin the slow flight demonstration? First, climb to an altitude no lower than 1,500 feet agl. Then clear the area by turning 90 degrees left and right to spot any nearby airplanes that could pose a conflict. Next, reduce power until the airplane begins slowing, and hold back pressure on the elevator to maintain altitude. Now configure the airplane according to the instructor’s (or examiner’s—you’ll have to demonstrate slow flight on your private pilot checkride) guidance. That means putting down flaps or landing gear in retractable-gear airplanes. Reduce power some more until the stall horn or light begins to chirp or flicker. Add just enough power to stop the warning and arrest any descent.

You’re bound to notice that the airplane wants to sink, what with the low power setting and all that drag from the flaps and landing gear hanging in the breeze. Here’s where technique becomes important. You’ll have to add power—a lot of it—to hold altitude and keep your airspeed five to 10 knots or so above the stall speed, enough that the stall warning doesn’t come on. And even more power as you make any requested turns, climbs, or descents.

In the region of reversed command, commonly called the "back side of the power curve," lower airspeeds require higher power settings to hold altitude. At these airspeeds, even adding full power may not be enough to climb or maintain altitude; it may be necessary to lower the airplane's pitch attitude to regain airspeed before climbing.
In the region of reversed command, commonly called the "back side of the power curve," lower airspeeds require higher power settings to hold altitude. At these airspeeds, even adding full power may not be enough to climb or maintain altitude; it may be necessary to lower the airplane's pitch attitude to regain airspeed before climbing.

To make things even more complicated, test standards require that you maintain your altitude within plus or minus 100 feet, your airspeed within plus-10 and minus-0 knots, your heading within 10 degrees of your target heading, and hold any bank angles within plus or minus 10 degrees.

Recovery is a bit simpler. Add power and lower the nose, then gradually retract flaps and landing gear until airspeed returns to normal values.

What’s it feel like in slow flight? The airplane’s nose is pitched up, so much that you may not be able to see the horizon ahead. Your airspeed is, well, slow. The power is blasting away, so the propeller’s P-factor wants to make the airplane turn left. This means that lots of right rudder may be needed to stay on heading and keep the inclinometer (“rudder ball”) centered. Plus, when maneuvering you’ll have to add enough power, or jockey it, to prevent any stall warning cues and arrest any descents or climbs from the target altitude. It’s a busy time!

So why is coming to terms with slow flight so important? Because you need to be able to instinctively recognize when you’re flying on the “back side” of the power curve, and when airspeeds and power settings are too low to prevent a loss of control or an uncommanded descent. In normal flight, pitch controls altitude and power controls airspeed. But when flying on the back side of the power curve, also called the region of reversed command, it’s the other way around. Power helps maintain altitude, and pitch controls airspeed.

Get too slow in the pattern or on final approach, and sense the airplane losing altitude in a mushing descent? That’s a sign you’re on the back side of the power curve, and need to speed up and climb away at VX or VY to prevent a hard landing, or worse. On a takeoff leg, is your climb rate faltering as your airspeed bleeds off? Time to both add power and lower the nose for a more energetic, safer climbout. Last but certainly not least, are your stall warnings going off? Again, it’s time to power up and lower the nose to reduce your angle of attack. You’ve gone from slow flight into a full-blown stall, and fast action is now the rule.

Before 2018, the FAA’s practical test standards for the private pilot checkride used to require candidates to demonstrate flight at the slowest possible airspeed, even if it meant flirting with a stall. Today, that goal has been changed to fly slowly but to avoid a stall. It’s a change in semantics, but let’s be frank. Slow flight by any name is a maneuver designed to sharpen our senses and techniques, so we avoid the hairy edge of a stall and react fast enough to prevent departing from controlled flight.

Illustration by Charles Floyd
Illustration by Charles Floyd
Thomas A. Horne

Thomas A. Horne

AOPA Pilot Editor at Large
AOPA Pilot Editor at Large Tom Horne has worked at AOPA since the early 1980s. He began flying in 1975 and has an airline transport pilot and flight instructor certificates. He’s flown everything from ultralights to Gulfstreams and ferried numerous piston airplanes across the Atlantic.

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