How is Reference Zero computed?

Reference Zero is a critical calculation in flight operations that helps in understanding the aircraft's performance during takeoff. The correct method for computing Reference Zero involves adding the Takeoff Ground Run to the Takeoff Flare distance.

The Takeoff Ground Run is the distance required for the aircraft to accelerate to the point where it begins to take off, while the Takeoff Flare distance is the amount of distance the airplane needs to safely transition from its ground run into flight. By adding these two distances together, pilots can determine a comprehensive threshold that ensures they have adequate runway length to achieve a safe takeoff.

This computation is essential for ensuring that the aircraft can take off safely given the atmospheric conditions, aircraft weight, and runway length. It provides a more complete picture of the aircraft's required runway distance than other methods, making it crucial for flight planning and safety.

In contrast, the other options either focus on different phases of flight or combine metrics that do not pertain directly to the fundamental aspects of determining a safe takeoff distance.