AFT – A position relative to a reference point closer to the tail of the aircraft.
BL (Bu*t line) – Distance measured to the left or right of (and parallel to) the vertical centerline of the fuselage.
CHORDLINE – A line joining the leading and trailing edge of an airfoil.
DIHEDRAL - Looking at an aircraft from the front, most wings form a positive angle relative to horizontal. This is called dihedral.
FWD (FORWARD) – A position relative to a reference point closer to the nose of the aircraft.
FS (FUSELAGE SECTION) – Distance measured fore or aft of a specific point on the fuselage.
INBOARD – Toward the longitudinal centerline (BLO) of the aircraft.
LEFT – A position relative to a reference point corresponding to the pilot’s left side when seated, facing forward in the aircraft.
LONGERON – A structural member of the aircraft running fore and aft.
OUTBOARD – Away from the longitudinal centerline (BLO) of the aircraft.
RIGHT – A position relative to a reference point corresponding to the pilot’s right side when seated, facing forward, in the aircraft.
SHEARWEB – The vertical member of a spar.
SPAR – The primary spanwise airfoil structural component.
SPAR CAP – The top and bottom members of a spar, usually horizontally oriented.

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