One Engine Inoperative Procedures
The Federal Aviation Regulation (FAR) Part 25 requires a two engine Transport Category Aircraft to be able to climb at a slope of 62.5:1 with one engine inoperative in order to receive its operating certificate from the Federal Aviation Administration. This slope is a minimum aircraft certification, one engine operative performance standard and has nothing to do with obstacle clearance. Airlines do not use this slope to calculate takeoff performance during daily operations.
The Federal Aviation Administration also uses a 62.5:1 slope as an “Obstacle Identification Surface”. Objects which penetrate this surface are identified to the airlines for the purpose of planning takeoff weights for obstacle avoidance.
Airlines must load their aircraft in such a manner as to be able to clear obstacles identified by means of the Obstacle Identification Surface by 35 feet vertically or 300 feet horizontally in the event of a one engine inoperative situation on takeoff.
Airlines pilots do not perform preflight takeoff weight planning based on airline one engine inoperative procedures since FAR Part 25 requirements establish engineering standards. Pilots make dynamic flight planning decisions based on operational requirements such as type of aircraft in use, airport elevation, wind direction and speed, temperature, pressure, location and height of identified obstructions, and the requirements prescribed by the appropriate FARs.