Definition
An unintended pitch attitude in which the aircraft's nose has risen above the desired level-flight position, typically detected on instruments by an altimeter showing a climb, a vertical speed indicator showing a positive rate, and an airspeed indicator showing a decrease.
Plain English
The nose has drifted up when it shouldn't have. The plane is climbing when you wanted to stay level, and the airspeed is bleeding off as a result.
Context Anchor
Seen during instrument flying when using the altimeter to hold altitude in straight-and-level flight.
Derivation
Deviation comes from a Latin idea meaning “to turn aside from the way.” In flying, a deviation is the airplane moving away from the attitude, altitude, heading, or path the pilot intended.
Why Pilots Care
Uncorrected nose-high deviations produce altitude excursions that can violate assigned altitudes or create unsafe closure with traffic or terrain.
Grounding Statement
If the altimeter is showing a steady increase while you meant to stay level, the airplane is likely being flown with the nose too high.
Intuition Check
Nose-high does not mean the nose looks dramatically high outside. In instrument flying, even a small nose-up error can be enough to show up as an altitude gain.
Example Sentence 1
The student noticed a nose-high deviation when the altimeter began to wind up and airspeed slowly decreased, so she relaxed back-pressure to return to level flight.
Example Sentence 2
A small nose-high deviation during altitude hold practice caused the altimeter to climb steadily at 80 feet per minute.