[...]
The outer surface, shown on Transport Canada Fort Smith Zoning Plan dated August 30, 1978, is an imaginary surface located at a common plane established at a constant elevation of 45.7 m above the assigned elevation of the airport reference point except where that common plane is less than 9.1 m above the surface of the ground, the imaginary surface is located 9.1 m above the surface of the ground.
[...]
