ILS (instrument landing system) reference datum The point at a specified height that is located vertically above the intersection of the runway centerline and the threshold and through which the downward extended straight portion of the glide path passes.

[¦ī¦el¦es ′ref·rəns ‚pȯint] (navigation) A point that is on the centerline of a runway served by an ILS and that is designated as the optimum point of contact for the landing aircraft. Derived from instrument landing system reference point.

The reference datum is an imaginary vertical plane from which horizontal distances are measured for aircraft weight and balance purposes. The datum is determined by the manufacturer, and in small aircraft, the reference datum is often located along the firewall or at the leading edge of the wing.

The reference datum for an given aircraft type is defined by the manufacturer. It may be at a specific aircraft station or, in many cases, it may be at a specified distance forward of the aircraft nose to simplify centre of gravity calculations. Arms and moments are calculated based on the reference datum.

Threshold Crossing Height Defined [FAA Pilot/Controller Glossary, PCG, 8/22/13] THRESHOLD CROSSING HEIGHT− The theoretical height above the runway threshold at which the aircraft’s glideslope antenna would be if the aircraft maintains the trajectory established by the mean ILS glideslope or MLS glide path.

Instrument Landing System
Definition. Instrument Landing System (ILS) is defined as a precision runway approach aid based on two radio beams which together provide pilots with both vertical and horizontal guidance during an approach to land.

The horizontal reference datum is an imaginary vertical plane or point, placed along the longitudinal axis of the aircraft, from which all horizontal distances are measured for weight and balance purposes. There is no fixed rule for its location, and it may be located forward of the nose of the aircraft.

From Wikipedia, the free encyclopedia. In aviation, reference datum height (RDH) is the height of a point, located above the intersection of the runway centre line and the threshold, through which the downward extended straight portion of the glide path passes.

The value of the ILS Reference Datum Height (ILS RDH) is coded using the Glidepath.rdh and the Glidepath.rdhAccuracy attributes. Accoding to ICAO Annex 10, the height of the ILS reference datum for ILS will be 15 m (50 ft). A tolerance of plus 3 m (10 ft) is permitted. The corresponding data type for the RDH value contains an uom attribute.

What Are Datums? A datum is a plane, a straight line, or a point that is used as a reference when processing a material or measuring the dimensions of a target. A datum is defined as follows in the ISO standard:

In aviation, reference datum height ( RDH) is the height of a point, located above the intersection of the runway centre line and the threshold, through which the downward extended straight portion of the glide path passes. It is usually found on the aerodrome instrument approach charts.

A real (non-ideal) integral feature of a target used for establishing a datum (e.g. surface of a part or hole). An actual surface with sufficiently precise shape that comes into contact with a datum feature and is used for establishing a datum (e.g. surface plate, bearing, and mandrel ).