Definition
A fixed pointer at the top of the attitude indicator that, together with the banking scale, shows the aircraft's angle of bank. The index points to graduations on the scale (typically 10°, 20°, 30°, 45°, 60°, and 90°) to indicate how far the aircraft is banked left or right.
Plain English
A small marker at the top of the attitude indicator that lines up with a curved scale to show how steeply the aircraft is banked.
Context Anchor
Seen on the attitude indicator when checking or controlling the airplane’s bank during turns, especially when flying by instruments.
Derivation
Index' comes from Latin 'index,' meaning 'pointer' or 'one that points out.' The bank index is literally the pointer that shows the bank angle.
Why Pilots Care
Precise bank control is required for coordinated turns, accurate heading changes, and preventing unusual attitudes during instrument flight.
Intuition Check
Bank here does not mean a financial bank; it means the airplane is tilted left or right. Index here does not mean a list in a book; it means a reference mark on the instrument.
Example Sentence 1
Rolling into the turn, she watched the bank index settle on the 30° mark.
Example Sentence 2
During the standard-rate turn the bank index stayed aligned with the 30-degree line on the scale.