Definition
A vertically oriented compass card display, shaped like a small rotating drum, that shows only a narrow segment of headings through a window on the face of the heading indicator. As the aircraft turns, the drum rotates behind the window so the current heading appears centered, with adjacent headings visible to either side.
Plain English
Instead of a flat round dial, the heading numbers are printed on a small turning cylinder. You see only a small slice of it through a window, like looking at part of a rolling barrel.
Context Anchor
Seen on some heading indicators when the pilot reads the aircraft’s direction from the instrument panel.
Derivation
Called drum-like because the rotating part is shaped like a drum, a short cylinder, rather than a flat disc. The card refers to the printed scale of headings wrapped around it.
Why Pilots Care
Pilots need to recognize this presentation because reading a drum-style heading indicator is slightly different from reading the more common round card. Only a small range of headings is visible at once, so quick scanning during turns takes a little practice.
Intuition Check
Do not read “card” here as a paper card or checklist item. In this instrument context, it means the marked moving display inside the heading indicator.
Example Sentence 1
The heading indicator in this aircraft uses a drum-like card, so the pilot reads the current heading through a small window at the top of the instrument.
Example Sentence 2
As the airplane turned, the drum-like card rotated smoothly past the lubber line to show the new heading.