The lowest altitude or height above the elevation of the relevant runway threshold or the airport elevation as applicable, used in compliance with appropriate obstacle clearance criteria. Obstacle clearance altitude is referenced to mean sea level and OCH to the threshold elevation or in the case of non-precision approaches to the airport elevation or the threshold elevation if that is less than 2 m (7 ft) below the airport elevation. An obstacle clearance height for a circling approach is referenced to the airport elevation. For convenience, when both expressions are used they may be written in the form “obstacle clearance altitude/height” and abbreviated “OCA/H” (ICAO). The calculated OCA/H is the height of the highest obstacle, or
equivalent missed approach obstacles, plus an aircraft-related allowance. In assessing these obstacles, the operational variables of the aircraft category, approach coupling, category of operation, and missed approach climb performance are considered.