How does runway analysis ensure obstacle and terrain clearance?

The FAA has published AC 120-91A, “Airport Obstacle Analysis,” which provides acceptable methods and guidelines for takeoff and climb obstacle analysis. ICAO has a similar publication that closely mirrors the AC 120-91A guidelines but includes slight variations, such as the width of the obstacle corridor considered. These publications and their methods are used in the obstacle analysis evaluation for each takeoff. 

Note that the ability exists to set which obstacle corridor is considered in the obstacle analysis. Navigate to MORE > AIRCRAFT > YOUR AIRCRAFT > FIELD PERFORMANCE and in the Takeoff group, select your Obstacle Corridor for your aircraft and operation.