Definition
A characteristic of an airplane's design that determines how it responds when displaced from a trimmed flight condition. An airplane with positive stability tends to return to its original flight condition on its own after being disturbed. An airplane with neutral stability remains in the new condition after being disturbed, neither returning to the original condition nor moving further away from it.
Plain English
Positive stability means the airplane wants to return to where it was after a bump or input. Neutral stability means the airplane stays wherever you leave it, without drifting back or getting worse. Most training airplanes are designed to be positively stable so they help the pilot rather than fight them.
Context Anchor
Seen in steep-turn discussions when explaining how an airplane behaves as bank angle changes and why the pilot may need to hold or correct bank pressure.
Derivation
Stability' comes from the Latin 'stabilis,' meaning steady or firm. 'Positive' here means 'acting in favor of returning to the original condition,' and 'neutral' means 'not acting either way.' The terms describe which direction the airplane's tendency points after a disturbance.
Why Pilots Care
In steep turns this behavior determines how much continuous control input the pilot must apply to keep the desired bank and pitch; unwanted pitching or rolling tendencies increase workload and can lead to altitude or airspeed deviations.
Analogy
Positive stability is like a marble in a bowl: if you move it, it tends to roll back toward the center. Neutral stability is like a marble on a flat table: if you move it, it tends to stay where you left it.
Intuition Check
Positive does not mean “good,” and neutral does not mean “safe to ignore.” Here, they describe what the airplane naturally tends to do after it is disturbed.
Example Sentence 1
Because the trainer has positive stability in roll, the pilot must hold a small amount of aileron into the steep turn to keep the bank from shallowing out on its own.
Example Sentence 2
During the steep-turn practice the instructor noted the airplane exhibited neutral stability, remaining at the new bank angle after a small gust instead of rolling back toward wings level.