What are the three imaginary lines that pass through an aircraft’s center of gravity at 90-degree angles to each other called?

• A. Axes of an Aircraft
• B. Central Lines
• C. Reference Frames
• D. Control Axes

Answer: (A)

The concept being tested is the fixed coordinate system that describes an aircraft’s orientation in space. These are the three imaginary lines that pass through the aircraft’s center of gravity and are mutually perpendicular, forming the axes of an aircraft. They provide a reference frame for motion: the longitudinal axis runs nose to tail, the lateral axis runs wingtip to wingtip, and the vertical axis runs top to bottom. Rotations about these axes correspond to the basic flight motions—roll about the longitudinal axis, pitch about the lateral axis, and yaw about the vertical axis. This is why the standard term is “axes of an aircraft.” Other terms like central lines or reference frames aren’t the conventional name for this fixed body-coordinate system, and while control axes can appear in some contexts, the typical, widely accepted term for these three perpendicular lines is axes of an aircraft.