The International Civil Aviation Organization (ICAO) defines decision height or decision altitude as a specific altitude. It’s the lowest height/altitude in the approaching descent or a private place. If the pilot cannot determine the visual reference of the approach, the pilot must then initiate a missed approach.
A missed approach is the procedure undertaken by a pilot when an instrument approach cannot be completed. Air traffic control may assign instructions to the pilot prior to clearance being given for approach and landing. Typically a pilot will determine if the approach can be made safely by the time the aircraft reaches the decision height.
Decision Height vs. Decision Altitude
A decision height (DH) is measured above ground level. A decision altitude (DA) is measured above mean sea level. Both are used for precision approaches. DH and DA are given at the destination airport and are established to allow enough time to safely reconfigure a private plane to climb and initiate a missed approach.
A Pilot’s Decision
In the grand scheme of things, decision height is only one of many factors a pilot must be familiar with when approaching its destination. Some of the factors to be considered include:
- True airspeed
- Rate of descent
- Weather conditions
- ATC communication