We don't have synonyms for deep stall yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are deep state.
(n) :
(aviation) An extremely dangerous type of aerodynamic stall (sudden loss of lift caused by airflow separation) where the angle of attack of a T-tailled aircraft becomes so high that the horizontal stabilizer and elevators are blanketed by the turbulent wake of the main wings, rendering the stabilizer and elevators ineffective and often preventing recovery from the stall.
(n) :
(aviation) An extremely dangerous type of aerodynamic stall (sudden loss of lift caused by airflow separation) where the angle of attack of a T-tailled aircraft becomes so high that the horizontal stabilizer and elevators are blanketed by the turbulent wake of the main wings, rendering the stabilizer and elevators ineffective and often preventing recovery from the stall.