Definition
The horizontal reference line on the attitude indicator that represents the natural horizon. The miniature airplane symbol on the instrument is positioned relative to this bar to show the airplane's pitch and bank attitude in flight.
Plain English
The line across the middle of the attitude indicator that stands in for the real horizon outside. The little airplane symbol sits above it, below it, or tilted against it to show whether the nose is up, down, or banked.
Context Anchor
Seen on the attitude indicator during attitude control, especially when flying by reference to instruments instead of the outside view.
Derivation
“Horizon” comes from an old Greek word meaning “boundary,” referring to the line where the earth and sky seem to meet. “Bar” means a straight strip or line. Together, “horizon bar” means the straight line on the instrument that stands in for the real horizon.
Why Pilots Care
It supplies the visual reference needed to maintain level flight and coordinated turns when the natural horizon is obscured by clouds, darkness, or haze.
Intuition Check
The horizon bar is not the actual outside horizon. It is the instrument’s horizon reference used to judge the airplane’s attitude.
Example Sentence 1
As the airplane climbed, the miniature airplane symbol rose above the horizon bar on the attitude indicator.
Example Sentence 2
A slight left bank was corrected when the horizon bar returned to level with the wings of the miniature airplane.