Lofting coordinates

Lofting coordinates are used for aircraft body measurements. The system derives from the one that was used in the shipbuilding lofting process, with longitudinal axis labeled as "stations" (usually fuselage stations, frame stations, FS), transverse axis as "buttocks lines" (or butt lines, BL), and vertical axis as "waterlines" (WL). The lofting coordinate frame is similar, but not the same as aircraft principal axes used to describe the aircraft flight. For the US-manufactured aircraft the ticks on the axes are labeled in inches,^[1] (for example, WL 100 is 100 inches above the base waterline).