In a nonradar environment, how far in miles must a departure take off before an arrival leaves a fix inbound if the takeoff direction differs by at least 45° from the final approach course?

In a nonradar environment, when a departure is taking off in a direction that differs by at least 45° from the final approach course of an arrival, the required separation distance is critical in ensuring safety and minimizing the risk of collisions. The standard distance that a departure must take off before an arrival leaves a fix inbound is 4 miles.

This separation requirement is based on the need to ensure that the two aircraft have sufficient lateral distance from each other given their differing flight paths. Allowing for 4 miles helps account for the potential for lateral drift and ensures that the arrival can safely proceed to the landing without interference from the departing aircraft.

Here, the choice of 4 miles as the answer is rooted in established Air Traffic Control procedures that aim to maintain safety and efficiency in airspace, particularly in nonradar environments where positional awareness may not be as precise as in radar situations. Understanding these requirements is crucial for ensuring safe operations in cases where the flight paths of departing and arriving aircraft may intersect at different angles.