Definition
A small pitch adjustment on the attitude indicator equal to half the thickness of the miniature aircraft's wing bar, used to make precise corrections during straight-and-level flight when an altitude deviation is small. The wing bar of the miniature aircraft on the attitude indicator serves as a measuring reference, and a half-bar movement up or down represents a slight, controlled change in pitch attitude.
Plain English
When you're a little off your altitude, you nudge the nose up or down by an amount equal to half the width of the little airplane symbol on your attitude indicator. It's a small, measured pitch change rather than a big one.
Context Anchor
Seen when using the altimeter and attitude indicator together to maintain straight-and-level flight by reference to instruments.
Derivation
The 'bar' refers to the horizontal wing bar of the miniature aircraft symbol on the attitude indicator. Pilots learned to use the thickness of that bar as a built-in ruler for measuring small pitch changes, so 'half a bar width' became shorthand for a small, standardised correction.
Why Pilots Care
Allows the pilot to hold altitude more accurately and avoid unnoticed deviations that could lead to terrain clearance issues or airspace violations.
Analogy
It is like making a tiny steering correction to stay centered in a lane instead of jerking the wheel every time the car drifts slightly.
Intuition Check
Do not read this as correcting only half of the altitude error. It means the size of the pitch change is about half the thickness of the attitude indicator’s horizon bar.
Example Sentence 1
When she noticed the altimeter had drifted up 50 feet, she made a half bar width correction nose-down to ease back to assigned altitude.
Example Sentence 2
To stay at 4,000 feet without creeping high, the pilot used a half bar width correction on the three-pointer altimeter.