Definition
The angle, measured in degrees, between the aircraft's lateral axis and the horizon when the aircraft is rolled to one side. Bank angle is displayed on the attitude indicator against a banking scale, typically marked at 10°, 20°, 30°, 45°, 60°, and 90°.
Plain English
How steeply the aircraft is tilted left or right, measured as an angle. A wings-level aircraft has zero degrees of bank; the more the wings are tipped, the higher the number.
Context Anchor
Seen during instrument flying when controlling turns and checking how quickly the aircraft is changing heading.
Derivation
Bank' comes from old nautical and aeronautical use meaning to tilt or lean to one side. Measuring that tilt 'in degrees' gives pilots a precise, repeatable number to fly to, rather than a vague sense of 'a little' or 'a lot.'
Why Pilots Care
The bank angle directly affects how quickly the heading changes during a turn.
Intuition Check
Bank does not mean money or the side of a river here; it means the airplane is tilted left or right. Degrees does not mean temperature here; it means an angle.
Example Sentence 1
Rolling into 20 degrees of bank, the pilot established a standard rate turn to the new heading.
Example Sentence 2
Increasing the degrees of bank beyond 30 can lead to a steeper turn and higher load factor.