What is the purpose of the center line on an aircraft drawing?

• A. It marks the center of gravity.
• B. It divides a part into symmetrical halves.
• C. It indicates flight direction.
• D. It shows the cut line locations.

Answer: (B)

The center line marks the longitudinal axis of symmetry of the part or entire aircraft, serving as the main reference for locating features so that the left and right sides are mirror images. On drawings, dimensions and features are often positioned relative to this axis, making it easy to verify alignment and ensure that holes, ribs, or other details are properly centered about the aircraft’s centerline. This is not a designation of the center of gravity, nor does it indicate flight direction or cut line locations. The centerline simply provides a consistent, symmetry-based reference that keeps features balanced around the axis.