- Decision altitude (DA) is referenced to mean sea level and decision height (DH) is referenced to the threshold elevation.
- Category II and III minima are expressed as a DH and not a DA. Minima is assessed by reference to a radio altimeter and not a barometric altimeter, which makes the minima a DH.
- The required visual reference means that section of the visual aids or of the approach area which should have been in view for sufficient time for the pilot to have made an assessment of the aircraft position and rate of change of position, in relation to the desired flight path.
Decision Altitude (DA)/Decision Height (DH) [ICAO]
Source: Pilot Contoller Glossary (PCG)