How is TODA determined?

The Takeoff Distance Available (TODA) is determined by taking the Takeoff Run Available (TORA) and adding any available clearway beyond the runway's physical limits that can be used to enhance takeoff performance. The clearway is a defined area beyond the end of a runway that provides extra room for an aircraft during takeoff and is free from obstacles, allowing for a safer ascent.

This method of calculating TODA is crucial because it provides pilots with important information about how much distance is realistically available for takeoff, considering the potential extension provided by the clearway. It helps ensure sufficient distance is available for the aircraft to reach a safe altitude in case of an engine failure or other issues during the takeoff phase.

The other options do not accurately describe the mechanics of determining TODA. Subtracting landing distance or calculating average runway gradient does not relate to how TODA is calculated, and simply assessing environmental conditions does not provide a clear formula for determining available takeoff distance. Understanding the elements contributing to TODA is key in flight operations, especially in ensuring safety and compliance with performance requirements.