Final answer:
Obstacle climb gradients refer to the required performance for an aircraft to clear obstacles during takeoff, and one engine inoperative (OEI) conditions require meeting climb gradients with one engine not functioning, ensuring safety in the event of engine failure.
Step-by-step explanation:
The rule regarding obstacle climb gradients generally refers to the required performance for aircrafts to clear obstacles during the takeoff climb phase under specified conditions. The climb gradient can be defined as the altitude gain per 100 units of forward travel. In aviation, regulations typically require specific climb gradients to be met to ensure that an aircraft can safely clear obstacles after takeoff.
For one engine inoperative (OEI), this represents a more stringent condition, as the aircraft must be able to meet climb gradient requirements with the critical engine inoperative, representing the worst-case scenario. This ensures aircraft safety in the event of an engine failure during or immediately after takeoff.
OEI climb gradients are determined during the certification process for aircraft and are used for performance planning, especially during takeoff. Pilots will use performance charts or aircraft computers to calculate if they can meet the required OEI climb gradients before departure, which may be influenced by variable factors such as aircraft weight, ambient temperature, and airport elevation.