Question: How and when should I populate the heightAboveTouchdownZone attribute of the Obstacle feature class?

Answer: Populate this attribute when an obstacle is within the Vertically Guided Approach Surface (VGAS) and Vertically Guided Protection Surface (VGPS) associated with a specific Runway End. In these cases, set the value to the difference between the height of the obstacle and the Touchdown Zone Elevation, which is the highest elevation along the runway centerline within the first 3,000 feet from the threshold as determined from the centerline profile data. Enter the distance in U.S. Survey Feet.

Where an obstacle is not associated with either of these surfaces, set this value to 0.

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