What is the purpose of the downwind leg in flight?

The downwind leg is an essential part of the traffic pattern during landing and is defined as the flight path that is parallel to the runway but in the opposite direction of landing. This configuration allows the pilot to establish a safe and predictable approach for landing. While flying downwind, the pilot prepares for the next stages of the landing process, including the base leg and final approach.

By flying parallel to the runway, the pilot can maintain a safe distance from the runway environment while still aligning with the intended landing path. It also provides an opportunity to assess the aircraft's speed and configuration, ensuring that it enters the final approach correctly and safely.

Other options describe flight paths that do not accurately represent the downwind leg. The perpendicular path mentioned in one option does not relate to how traffic patterns are organized, and the straight flight towards the runway and initiating takeoff from the runway pertain to different phases of flight entirely. Thus, the definition of the downwind leg aligns properly with the correct choice.