Definition
A reference mark on the bank index of an attitude indicator positioned at 45 degrees of bank, used by the pilot to set or verify a precise 45° angle of bank during instrument maneuvers such as steep turns.
Plain English
A small tick mark on the attitude indicator that shows where the pointer lines up when the airplane is banked exactly 45 degrees left or right.
Context Anchor
Seen on the attitude indicator or primary flight display when practicing or checking bank angle during instrument flight.
Derivation
Hash mark' comes from the everyday term for a short tick or slash used as a marker on a scale. On the attitude indicator's bank scale, the mark sits at the 45° position — hence '45° hash mark.'
Why Pilots Care
Allows fast confirmation of 45-degree heading increments during turns without counting individual degrees.
Analogy
Like the quarter marks on a clock face, but aligned to compass directions.
Intuition Check
Do not read 45° as a compass direction here. It means the airplane is banked 45 degrees away from wings-level flight.
Example Sentence 1
Rolling smoothly into the turn, she stopped the bank pointer right on the 45° hash mark and began trimming for the steep turn.
Example Sentence 2
Timing the turn between two 45° hash marks gave a precise 90-degree heading change at standard rate.