CONFIDENTIAL #2
ANNEX C
Flight path protection
Aircraft should be able to approach or depart from an airport in an unobstructed flight path, free from both natural and man-made obstacles. The latter are normally controlled by legislation limiting construction in certain areas, and the former are usually overcome by careful alignment of the runway. International standard criteria (called Obstacle Limitation Surfaces) have been developed and agreed to define what should constitute obstacle-free approach and departure paths for airports and to provide protection for low flying aircraft in the areas around airports.
2.
These criteria, which cover a large area around an airport, are called "surfaces" because they project hypothetical planes and ramps at specific heights and slopes around the airport. Anything protruding through the "surface" is considered to be a hazard to aircraft.
3.
If it was possible to see the "surface" when taking off it would appear as an inclined ramp 180m wide which starts 60m from the end of the runway. The ramp would be sloping upwards at a gradient of 1 in 50 (2%) and it would be getting wider (at a divergence of 12%) until it reached a total width of 1,200m, when it would stay at that width until the ramp came to an end 15,060m from the end of the runway. Similarly, when approaching the airport the ramp would first appear beneath the aircraft 15,060m from the end of the runway, where it would be 4,800m wide. The surface would be sloping downwards at 1 in 40 (2%), and getting narrower; at 3,060m from the end of the runway the gradient would change to 1 in 50 (2%). It would reach runway level at 60m from the end of the runway, and would by then have narrowed to 300m.
4.
The attached sketch shows approximately where the "surface" for an airport at Chek Lap Kok would be.
CONFIDENTIAL
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