This document specifies requirements for an Airborne Landing Guidance System (ALGS) electronic device. This equipment shall derive relative aircraft position and situation information for flight along precision three-dimensional paths within the appropriate coverage area. The precision threedimensional path may be an ILS straight-in look-alike path or a complex, curved path. The requirements are applicable to electronic devices capable of receiving signals or other information from one or more sources, including but not limited to ILS, MLS, GNSS, or IRU inputs.