Definition
A flight situation in which the airplane's total energy — the combination of airspeed (kinetic energy) and altitude (potential energy) — is being lost faster than the pilot can replace it, leading toward a stall, an excessive sink rate, or both if not corrected in time.
Plain English
A situation where the airplane is running out of speed and height at the same time, with very little margin left to recover before something bad happens.
Context Anchor
Seen in energy management discussions, especially during approach, slow flight, go-arounds, and situations where the airplane is close to the ground.
Derivation
‘Energy’ here refers to the airplane's working store of speed and height — the two things a pilot can trade back and forth to keep flying. ‘Depletion’ comes from Latin deplere, meaning to empty out. So the phrase literally describes a situation in which the airplane's reserves of speed and altitude are emptying out.
Why Pilots Care
Recognizing the condition early lets the pilot add power and adjust pitch before the aircraft reaches a stall or ground impact that cannot be corrected.
Grounding Statement
Picture a slow, nose-high approach where the airplane is sinking, the airspeed is bleeding off, and adding power alone is not arresting either trend — that is energy depletion in progress.
Intuition Check
Do not read “energy depletion” as fuel running out or battery power being low. Here it means the airplane is running out of the speed and height it needs to keep flying safely.
Example Sentence 1
The instructor demonstrated how a high sink rate combined with decaying airspeed on final could quickly turn into an energy depletion scenario if power and pitch were not coordinated.
Example Sentence 2
A high-drag configuration at low airspeed can create an energy depletion scenario if thrust is not increased right away.