What defines the departure leg of a traffic pattern?

The departure leg of a traffic pattern is defined as a rectangular path that extends straight out from the departure runway after takeoff. This leg represents the initial segment of the traffic pattern where an aircraft gains altitude and safely clears the obstacles and airspace around the airport.

In a typical traffic pattern, pilots will take off from the runway and maintain a specific flight path, which includes the departure leg leading away from the airport. This not only helps in maintaining separation from incoming and outgoing flights but also assists in transitioning to the next segment of the pattern, such as the crosswind leg.

The other options describe flight paths that do not accurately represent the characteristics of the departure leg. For instance, a straight course aligned with the landing runway does not account for the specific maneuvering required after takeoff. Meanwhile, a horizontal course that is perpendicular to the extended centerline or a course parallel to the landing runway in the opposite direction also do not fit within the defined parameters of a departure leg within an established traffic pattern.