Butt lines extend parallel to the longitudinal axis and are located on the fuselage.

• A. They extend parallel to the longitudinal axis and are on the wings.
• B. They extend perpendicular to the longitudinal axis and are on the fuselage.
• C. They are used to determine the center of gravity directly.
• D. Butt lines extend parallel to the longitudinal axis and are on the fuselage.

Answer: (D)