decision altitude

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decision altitude (DA)

i. A specified altitude or height in the precision approach at which a missed approach must be initiated if the required visual reference to continue the approach has not been established. The decision altitude is with reference to mean sea level, whereas the decision height is with reference to the threshold elevation. The required visual reference means that section of the visual aids or of the approach area that should have been in view for a sufficient time for the pilot to be able to assess the aircraft's position and change of position in relation to the desired flight path. In Category III operations, with a decision height the required visual reference is that specified for the particular procedure and operation. For convenience, where both expressions are used they may be written in the form of “decision altitude/height” and abbreviated “DA/H.” These terms replace minimum height (MH), minimum descent (MD), minimum descent altitude/height [MDA (H)], and minimum descent height (MDH).
ii. The height at which a decision must be made, during an ILS (instrument landing system) or PAR (precision approach radar) instrument approach, either to continue the approach or to execute a missed approach.