Definition
The second phase of a spin, occurring after the incipient phase, in which the airplane's angular rotation rate, airspeed, and vertical descent rate have stabilized and the flightpath has become close to vertical. In this phase the aerodynamic forces and inertia forces are in balance, and the airplane is rotating about a vertical axis at a relatively steady rate.
Plain English
The middle part of a spin where things have settled into a steady pattern — the airplane is turning, falling, and pitching down at a roughly constant rate rather than still building up.
Context Anchor
Used in spin training and spin procedure discussions to describe the stage between the initial spin entry and the recovery.
Derivation
Developed' comes from the Old French desveloper, meaning to unwrap or unfold. In aviation it carries the sense of something that has fully unfolded into its complete form — the spin has finished building up and is now showing its steady, mature behavior.
Why Pilots Care
Identifying this phase confirms the spin is stable, so the correct recovery sequence can be applied without delay and with awareness of the altitude required.
Grounding Statement
In the developed phase, the airplane has settled into the spin instead of merely entering it.
Intuition Check
Developed does not mean improved or made better here. It means the spin has fully formed and become established.
Example Sentence 1
Once the spin entered the developed phase, the instructor demonstrated the standard recovery procedure for the aircraft.
Example Sentence 2
The handbook notes that more altitude is typically needed to recover from the developed phase than from an incipient spin.