Definition
The region of slow flight where induced drag dominates and more power is required to fly at a slower airspeed than at a faster one. In this regime, reducing airspeed increases the power needed to maintain level flight, and the airplane becomes less stable in airspeed — slowing further requires still more power, not less.
Plain English
A speed range so slow that flying slower actually takes more power, not less. If you let the airspeed drop in this range, you need to add power just to keep from sinking — pulling back on the yoke alone will make things worse.
Context Anchor
Pilots encounter this term in slow flight, approach, go-around, and performance discussions, especially when learning how airspeed, pitch, power, and sink rate work together.
Derivation
The 'power curve' is a graph of power required versus airspeed. The curve dips to a minimum at one specific speed (called L/D max area), then rises again as the airplane goes slower. The rising portion to the left of that minimum is the 'back side' — flying slower than the most efficient speed.
Why Pilots Care
Operating here reduces stability and can produce unexpectedly high descent rates if power is reduced without a corresponding pitch change.
Grounding Statement
Picture a slow airplane on final approach: if it slows too much, it may start sinking faster even though the nose is up.
Intuition Check
Do not read “back side” as a physical part of the airplane or an engine problem. It means the slow-speed side of a performance graph where slower flight takes more power, not less.
Example Sentence 1
On short final, the instructor demonstrated how the airplane was on the back side of the power curve and required throttle, not back pressure, to arrest the descent.
Example Sentence 2
On final approach the pilot recognized the back side of the power curve and added power early to avoid a high sink rate.