To hold altitude, an airplane needs enough engine power to overcome drag. Plot that power required against airspeed and you get a U-shaped curve. Its left half is the famous back side of the power curve — the region of reversed command, where flying slower takes more power, and where a lot of low-and-slow accidents live. This page builds the curve from its two halves, shows why the controls feel backwards down there, lets you set up slow flight in that region, and then fly an approach into the trap.
Power required is just drag × speed, and drag has two parts that pull in opposite directions with airspeed. Parasite drag (skin, form, the airplane pushing air aside) grows with speed, so its power grows as V³. Induced drag — the price of making lift — is worst when you're slow and flying at a high angle of attack, so its power falls off as 1∕V. Add them and the total sags to a minimum at the minimum-power speed, then climbs away on both sides.
The bottom of the bowl — minimum-power speed — gives you the most time aloft per gallon (best endurance) and the slowest sink in a glide-power situation. It is not the same as best glide, which is minimum-drag speed and sits a bit faster (a line from the origin tangent to the curve). Add flaps and the whole curve lifts and shifts left: more drag everywhere, but you can fly slower before stalling.
Lay a power-available line (your throttle) across the curve. Where it crosses the curve, power required equals power available and you can hold altitude — and it crosses in two places. The fast one, on the front side, behaves normally: pull the throttle back and you slow down. The slow one, on the back side, is reversed: to fly and hold altitude at a slower speed you need to add power, because induced drag is winning. Drag the airspeed marker across the shaded region and watch the required power climb as you slow.
Excess power (available − required) is what climbs the airplane: rate = excess power ∕ weight. Between the two trim speeds you have spare power to climb; outside them you sink. On the front side speed is stable — a gust that slows you cuts drag and the airplane tends to recover. On the back side it's unstable — slow down a touch, drag jumps, you sink and slow further. That's why the back side demands active power control.
Slow flight is the maneuver where you go and live on the back side deliberately — flying just above the stall, at the ragged edge of the reversed-command region, to feel how the airplane handles down there before you ever meet it on final. The lesson it teaches is a control swap: pitch (trim) sets your airspeed, throttle sets your altitude. Trim for a slow target speed, then fly the altitude with power alone. Notice how much throttle it takes just to stay level — and that asking for a slower speed asks for more power.
Sweep the speed slider and watch the throttle-for-level mark trace the whole bowl: it falls as you slow toward the minimum-power speed, bottoms out, then climbs again as you slow past it — the moment it starts climbing you've crossed onto the back side, where slower costs more power. Slow flight lives right down at that bottom: high pitch, high angle of attack, sloppy controls, the stall horn moaning, and a lot of throttle just to stay level. Try to fix a sink by pulling to a slower speed and you dig the hole deeper; add power instead and you climb. It's where you drill power for altitude, pitch for airspeed until it's reflex by the time you meet it on short final.
You're on final, dragged in low with reduced power, sitting on the back side. You notice you're sinking below the aim point. The instinct is to pull back to stop the sink — and on the back side that's exactly wrong: the nose-up raises induced drag, bleeds airspeed, drives power-required up, and you sink faster. The fix is power for altitude, pitch for airspeed. Fly it both ways and watch what happens.
Same throttle, same weight, two techniques. Pulling to hold altitude walks you left along the power curve into an accelerating sink and, eventually, a stall right above the runway. Trading a little altitude to keep the airspeed — and adding power if you need to arrest the descent — keeps you flying. If the throttle simply isn't enough to hold altitude at any speed, the honest answer is lower the nose and go around: no pitch input can conjure power you don't have.