The Realm of Reverse Command

Parvez Dara, MD, ATP, Master CFII

There is a transactional paradigm that we as pilots adhere to: trading pitch and power. In our world of drag inducers: elevators, flaps, gear and speed brakes, the trade between pitch and power remains paramount. Let me explain.

On a summer day when the winds were light and the haze was certain. I was seated in the right seat with an exceptionally gifted pilot in the left seat of his M20R As we climbed up to our designated altitude in perfect harmony, he leveled out and looked at me and asked, with all the comforts of his expertise, “What next?”

What followed was an interesting example of the “U” shaped power curve demonstration. Flying at minimal controllable airspeed, I asked him to make 90 degrees turn to the left. He banked and the stall warning came on and then the quick buffet before the lift was about to dry out. He immediately undid his actions using rudder judiciously with the ailerons, and we were back to our steady slow speed, but this time we were descending, and the altimeter was giving up altitude at 300fpm. He slowly added power to maintain the altitude, but the altimeter was not having any of it as it continued to unwind, now a bit slowly. He added more power and pitch up a couple of degrees, and the stall warning came on again. Now his face started to redden a bit. He was flustered. “Damn” escaped his lips. And that is where we lay our tale… 

The Back Side of the Power Curve: Understanding the Region of Reverse Command

Every pilot no matter his or her expertise, eventually meets the moment when the airplane stops behaving the way the textbook diagrams promised. Airspeed is bleeding, the nose is high, power is already near the stops, and yet the vertical speed needle stubbornly remains below the zero. Instinct says pull. Ah! here is where the elements of mastered habits get dethroned. Only experience, if it has been hard-won, says the opposite. That moment is the pilot’s introduction to the back side of the power curve—the region of reverse command—where the familiar relationships between pitch, power, airspeed, and altitude quietly invert. This regime of flight, occurring below the airspeed for maximum lift-to-drag ratio (L/D max), inverts the familiar relationships between pitch, power, airspeed, and altitude. Mastery of it is not an academic exercise; it is a practical necessity for safe slow-speed flight, particularly on final approach, where energy mismanagement has claimed far too many aircraft. The aircraft in this attitude, feels heavy while the controls feel light. Everything seems counterintuitive. My friendly and capable pilot sits and wonders what to make of it?

Core aerodynamics

So, considering the “damn,” he uttered, I asked him to climb back to the altitude we had previously achieved and start the process again. Experience was going to be a great teacher rather than drawing diagrams on a piece of paper. But a simple explanation in the debrief was going to be necessary. The power-required curve is U-shaped. Its bottom sits at the airspeed for maximum endurance, roughly the speed for best lift-to-drag ratio. To the right, the front side, more speed demands more power to overcome rising parasite drag. To the left, the back side, induced drag takes over and does it. As the airplane slows, the wing must be flown at a higher angle of attack to keep producing the same lift. The total aerodynamic force remains perpendicular to the chord; at high angles of attack a large component of that force points rearward. That rearward component is induced drag, and it rises steeply and exponentially. The result feels like a contradiction: the slower you fly, the more power you need simply to hold altitude.

He had encountered this dynamic and had felt the controls as “mushy” or “sloppy.” But what he needed was to feel that even a small gust or a slight further pull on the stick produces a disproportionately larger increase in drag, the airspeed decay unless appropriate action by him was undertaken, to reduce the angle of attack and/or add power. At the left side of the curve, the airplane has become speed unstable. What felt solid and predictable on the front side of the “U” now required constant, deliberate attention. This time, he was on full alert, with I am sure, his heart hammering in his chest, this young lad was going to master the move. And he did. A quick learner. A smile burst out on his face, the particulates of knowledge and experience, coalesced and the “Aha” moment arrived. Trading full power for pitch, just to maintain altitude till he had traversed to the right side of the “U,” and was back in command.

Pitch-and-power relationship

That transactional relationship between pitch and power relationship reverses as we go from steady flight on the front side of the “U” to its back side. On the front side, pitch primarily controls altitude and power controls airspeed. On the back side, angle of attack becomes the primary control of airspeed, while power becomes the primary control of the vertical path. A higher airspeed now requires a lower power setting to stay level; a lower airspeed requires more power. This is not a claim that reducing power will automatically reduce airspeed. It is a statement about the power required to maintain altitude at different speeds. The distinction matters.

Having completed our maneuvers and with just a single bead of sweat on his eyebrow, we headed back to the airport for some take off and landings. Armed with this burst of knowledge and actual experience, he was a master at the controls. Knowing the distinction of pitch and power that matter more on final approach when the airplane is already low and slow is a key to good landings. A pilot on the backside of the curve, sees the runway rising in the windscreen, feels the sink, and pulls. The very thing we are not supposed to do. As the adage goes, “never try to stretch a glide.” But pulling on the yoke is ingrained in our desire to survive. The ground rush, the descent and tachycardia inducing landing phase all conspire to create some interesting physiological and psychological imperatives. As the nose comes up, induced drag spikes and the sink rate increases. Full power is applied, yet the airplane continues to mush toward the ground. And right at that moment is the transactional prayer with the Almighty. Nothing robs the capacity of presence than fear. The only reliable escape, however, is to lower the nose, trade what little altitude remains for airspeed, and go around if possible. There are scores of accident reports that describe variations of the same sequence: low, slow, powered up, and still descending. The airplane was not refusing to fly; it was obeying the drag polar.

Energy perspective

Energy is such an amorphous term. It is metaphorical so to speak, yet its management clarifies its importance in all phases of life. In aviation, total energy is the sum of potential energy (altitude) and kinetic energy (airspeed). It is important to remember, even when the total energy is adequate, but the distribution is wrong, the elevator remains the primary tool for redistribution. Coordinated pitch and power then manage the overall energy state. At an airport after I had just landed, I witnessed an aircraft on final. He had his engine howling as he descended to a thud on the runway announcing his arrival. To his credit, he taxied off the runway on the first taxiway. On disembarking, I saw him looking at his main gear. Fortunately, he was unscathed to fly another day.

Angle of attack remains the most immediate cue for how close the airplane is to running out of usable kinetic energy. Although the correct response is often counter-intuitive: lower the nose, accept a temporary loss of altitude, reduce angle of attack, and allow the airplane to accelerate into a more efficient portion of the curve, pilots seem reluctant or fearful. When altitude permits, this “push to float” trades a short-term first-order penalty for a favorable second-order gain in energy. A simple priority rule captures the practical hierarchy: if low and slow, fix the low first, then the slow; if high and fast, fix the fast first, then the high.

Density altitude sharpens the lesson. On a hot afternoon at a high-elevation airport the power available shrinks while the power required does not. The margin between the front side and the back side narrows. A pilot who has always flown at sea-level airports can slide onto the back side without recognizing the change until the airplane begins to feel heavy and unresponsive. The numbers on the airspeed indicator look familiar; the airplane’s behavior does not. It happened to me at St. John Airport (KSJN) in Arizona. I had three passengers and bags with full fuel as I taxied for departure on a 5300-foot runway in my G36 Bonanza. On a sunny late summer’s day, the density altitude at 11:30am was 9100 feet. I rolled onto the runway put in full power and felt the aircraft slowly trudge its way over the airport markings, the airspeed finally reached my desired 74 knots and I trimmed for take-off. The aircraft kept rolling on its mains with no desire to lift off. Half the runway was in the rear and then the lift arrived. I gently pushed the nose down to get a higher airspeed; the controls still were mushy and the aircraft felt heavy. Three quarters of the runway was behind me, and I was at 100 feet in the air. Garmin G1000 was yelling “taxiway, taxiway,” as I drifted to the left a bit, trying to hold the heading. Fortunately, at the departure end of the runway there were no trees, only a drop off into a valley. I kept the forward pressure on the yoke as the airspeed built to 85knots and then the feel and performance of the aircraft became solid quickly increasing to 120kts with a 750 fpm VSI, and the climb out became an uneventful departure. This sea-level pilot almost slid onto the back side realm of reverse command, without recognizing the change until the airplane began to feel heavy and unresponsive. The numbers on the airspeed indicator looked familiar; the airplane’s behavior did not. My friend on the right seat also a pilot, let out a slow rush of air into the microphone. Me? I will leave that to your imagination.

The back side of the power curve is not an exotic corner of the envelope reserved for test pilots. It is the regime of every short-field approach, every minimum-controllable-airspeed exercise, and every go-around begun a few knots too slow. The airplane does not negotiate. It responds only to angle of attack, power, and the resulting energy state. In the end, every pilot is an energy manager. Those who grasp why the power curve bends upward on its left side, and who practice the disciplined use of pitch and power that the regime demands, fly with a margin of safety that no checklist alone can provide. The region of reverse command is not merely a curiosity of aerodynamics; it is a fundamental boundary of controlled flight that every pilot must learn to respect—and, when necessary, to cross deliberately to the other side, and with full understanding. Those who rely solely on inherited technique may eventually discover, too late, that the ladder was never the real danger!

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