Definition
The region of slow flight in which more power is required to maintain level flight as airspeed decreases, because induced drag rises sharply at low airspeeds and high angles of attack. In this region, the normal relationship between throttle and speed is reversed: reducing airspeed requires adding power, not reducing it.
Plain English
It is the slow-flight zone where flying slower actually takes more power, not less, because the wing has to work much harder to keep the airplane in the air.
Context Anchor
Encountered during slow flight, approach-to-landing practice, and discussions of how an airplane behaves near stall speed.
Derivation
The name comes from the power-required curve, a graph plotting power needed against airspeed. The curve dips to a low point at the airspeed of minimum power, then rises again as the airplane slows further. Flight on the rising left-hand side of that dip is the 'backside' — slower than the bottom of the curve.
Why Pilots Care
Operating here can produce rapid altitude loss if power is not increased promptly; recognizing the condition explains the need for coordinated power and pitch changes to avoid a stall.
Grounding Statement
Picture the airplane flying very slowly with the nose high: it is still flying, but it is using extra power just to keep from settling downward.
Intuition Check
Do not read “backside” as meaning the engine is behind the airplane or that the airplane has low power. Here it means the slow-speed side of a power-needed graph, where slower flight requires more power.
Example Sentence 1
During slow flight practice, the instructor demonstrated how the airplane was operating on the backside of the power curve, requiring extra throttle just to hold altitude.
Example Sentence 2
On final approach at low speed the pilot recognized the backside of the power curve and added throttle to keep the airplane from sinking.