Definition
An aerodynamic condition in which an airplane, after stalling, becomes trapped at a very high angle of attack from which normal recovery is difficult or impossible. It typically occurs in aircraft with T-tails or rear-mounted engines, where the stalled wing's turbulent wake blankets the horizontal stabilizer and elevator, robbing them of the airflow needed to lower the nose.
Plain English
A stall the airplane gets stuck in. The wing is so far past its stalling angle that the disturbed air coming off it covers the tail, leaving the elevator with little clean air to work with. The pilot pulls back or pushes forward on the controls and the airplane barely responds.
Context Anchor
Encountered in stall awareness and recovery discussions, especially for airplanes with a high-mounted tail.
Derivation
Called "deep" because the airplane is deep into the stall — well past the angle where a normal stall begins, and beyond the range where standard recovery inputs work.
Why Pilots Care
Recovery may be impossible without special techniques or configuration changes, leading to rapid altitude loss and potential loss of the aircraft.
Grounding Statement
Picture the wing sending rough, broken air back over the tail, leaving the tail with too little clean air to push the nose down.
Intuition Check
Deep stall does not mean a normal stall at a low altitude. It means the airplane may be stuck in a stalled, nose-high condition because the tail is not getting clean airflow.
Example Sentence 1
The flight manual warns that the airplane's T-tail design makes it susceptible to a deep stall, so the stick pusher must be operational before flight.
Example Sentence 2
After the nose pitched up uncontrollably, the crew recognized they had entered a deep stall and applied the manufacturer’s recovery procedure.