Approach Surface Height
Calculate the height of an approach surface (or other obstacle limitation surface) at a given distance, h = (gradient ÷ 100) · distance, from the ramp gradient (%) and the horizontal distance from the surface origin (m). Obstacle Limitation Surfaces (OLS) are imaginary inclined planes projected from runway thresholds and around runways, defined by ICAO, delimiting the airspace that must stay clear of obstacles for safe landing and takeoff. The approach surface, for example, rises at a typical 2% (1:50) gradient from the runway strip end; any object (building, antenna, tree, terrain) penetrating it is an obstacle to be removed, lowered, marked/lit or, ultimately, leading to operational restrictions. This calculation gives the maximum allowed surface height at each point, to compare with the actual height of existing or proposed obstacles around the airport — the basis of land-use control in airport protection zones and the assessment of new developments. Enter the gradient and the distance.
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Approach surface height
The height of an approach surface (or of any other obstacle limitation surface) at a given distance is h = (gradient ÷ 100) · distance, obtained from the gradient of the slope (in %) and the horizontal distance measured from the start of the surface. Obstacle Limitation Surfaces (OLS) are imaginary inclined planes projected from the runway ends and around the runway, defined by ICAO, that delimit the airspace which has to remain free of obstacles for landing and take-off operations to stay safe. The approach surface, for instance, rises with a typical gradient of 2% (1:50) from the end of the runway strip, in the direction from which aircraft approach to land; any object — building, antenna, tower, tree or the terrain itself — that penetrates that surface is an obstacle that has to be removed, lowered, marked and lighted (with obstruction lights) or, as a last resort, leads to operational restrictions (such as raising the minimum descent altitude, which reduces the availability of the airport in poor weather). This calculation gives the maximum permitted height of the surface at each point, so that it can be compared with the actual height of obstacles that already exist or are proposed around the airport. It is the basis of land-use control in airport protection zones (which limit the height of buildings in the surroundings) and of the mandatory review of new developments — the familiar 'object projected into airspace' assessment that every tall building near an airport has to go through. Enter the gradient and the distance.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.