When must you coordinate with the receiving facility before an aircraft departs?

The correct choice emphasizes the requirement to coordinate with the receiving facility specifically when the departure point of an aircraft is less than 15 minutes flying time from the boundary. This is crucial for ensuring proper handoff and continuity of flight operations, as it helps the receiving facility prepare for the incoming traffic. Pre-departure coordination allows the receiving facility to make necessary adjustments to its traffic management and ensures that the aircraft will have the appropriate services available upon its approach.

This practice fosters effective communication between facilities, thereby enhancing safety and efficiency. When the aircraft is within this time frame, it necessitates coordination so that the facility is ready to accept the aircraft and integrate it into their air traffic system without delays.

The other options do not address the specific context required for pre-departure coordination. For instance, waiting for 10 minutes from the boundary may not sufficiently account for traffic management needs. Coordinating only when the aircraft is delayed overlooks the preventive measures that should be in place for timely operations. Coordination upon a pilot's request does not ensure that the necessary preparations are made in advance, which can lead to mismanagement during critical phases of flight.