Flight Operations Group

Airport Obstacle Analysis &
Aircraft Performance Planning

Airport Obstacle Analysis

Aircraft Performance Planning

Performance Planning Training Videos

Frequently Asked Questions & Hot Topics

Q. What airport characteristics factor into your runway analysis data?
A. Obstacles, slope, elevation, and runway lengths (i.e. TORA, TODA, ASDA, LDA).

Q. Am I really only clearing obstacles in my flight path by 35 feet?
A. No, there is a safety margin built into AFM performance data. This safety margin is outlined in Part 25 (Aircraft Certification), but involves a conservatism applied to the actual data gathered by the test pilots upon certification. This conservatism is accomplished in various forms, with the most commonly referred to being a Gross climb gradient reduced to Net climb gradient factor. This is a reduction in the actual aircraft’s climb performance as a function of the number of engines. The decrement ranges from 0.8% (2 engine aircraft) to 1% (4 engine aircraft) for first, second, and third segment climbs/acceleration. An example would be if you are clearing an obstacle by a NET 35 ft, and the obstacle is 2 NM off of the departure end of the runway, you will actually be clearing that obstacle by at least 135 feet. At 10 NM this becomes over 500 ft. To determine the actual aircraft height above the 35 foot NET height, simply multiply the gradient reduction, .008 for example, by the distance in feet, to the obstacle. Also, this is assuming the worst case scenario of losing the critical engine AT V1, continuing the takeoff, operating at the maximum weight allowed for that scenario, and the obstacle in question is the most limiting obstacle. If the engine failure occurs after V1, or you depart with a lower weight than the maximum for that scenario, you will further increase this safety margin.

Last updated: Monday, June 12, 2023