The approach for Billy Bishop is over the water. It would interfere with some new development in the port lands but nothing else. I'm assuming the OLS is also different there because it's used for smaller aircraft at sea level, so they can take a much steeper glide slope. Large aircraft at YYC...

It's about obstacle limitation surfaces - They are these big fanning areas that extend from runways into the surrounding airspace. If a building is inside the surface, it interferes with landing system signals. I believe that the rehab on 17R/35L extended the surface a bit more / creates a more...