Definition
The center reference point on the bank angle scale of an electronic attitude indicator, marking zero degrees of bank. The roll pointer aligns with this mark when the airplane's wings are level relative to the horizon.
Plain English
The mark at the top of the curved bank scale on a glass-cockpit attitude display that shows the airplane is wings-level. When the pointer sits on this mark, you are not banked left or right.
Context Anchor
Seen on a primary flight display or electronic attitude indicator when checking whether the airplane is banked left, banked right, or wings-level.
Derivation
Roll' refers to the airplane's rotation around its longitudinal axis (banking left or right). 'Scale' is the marked reference arc on the display. 'Zero' is the no-bank position. Together: the zero-bank reference on the roll scale.
Why Pilots Care
It gives the pilot an immediate visual cue that the aircraft is wings-level without needing outside references.
Intuition Check
Zero does not mean the airplane is not moving. Here, zero means no left or right bank is being shown on the attitude display.
Example Sentence 1
After the unusual attitude recovery, she rolled the airplane until the pointer was back on roll scale zero, then adjusted pitch.
Example Sentence 2
When the bank pointer moved away from roll scale zero, the display confirmed the airplane had entered a turn.