Decision height
In aviation, the decision height is understood to be the height above the threshold of the respective runway at which the cockpit crew of an approaching aircraft decides at the latest whether the approach is continued and ended with a landing or whether the approach is aborted and restarted . The decision height for an approach is based on the published minimum height for the approach and the approaching aircraft category, at which there is still freedom from obstacles ( obstacle clearance height , also OCH , or obstacle clearance altitude , also OCA ), as well as a height to be determined by the aircraft operator Security surcharge determined.
See also: maximum elevation figure (minimum sector altitude) for the cruise.
Instrument landing system
For precision approaches, e.g. B. with the instrument landing system (ILS) a distinction is made between two types of decision heights:
- The decision height (DH) describes the height above the ground and is always measured using a radar altimeter . It is used in ILS categories (CAT) II and III.
- The decision altitude (DA) refers to the height above sea level and is measured using a barometric altimeter . It is only used on CAT-I approaches.
Non-precision approaches NPA
With non-precision approaches, however, there are no decision altitudes as with a precision approach, but only minimum descent altitudes . The aircraft can sink up to this level and at this level until the missed approach point is to be seen also MAPt (missed approach point) continue to fly in accordance with, the approach lights or the runway. These sink heights are designated as follows:
- minimum descent height (MDH)
- minimum descent altitude (MDA)