When is air traffic control service provided on a first-come, first-served basis?

Air traffic control service provided on a first-come, first-served basis typically occurs when specifically requested by a pilot, and this is subject to certain exceptions that may override the standard procedure. The concept of first-come, first-served refers to the prioritization of flights based on their order of arrival or request for service.

In practical situations, when an aircraft requests air traffic control services, such as clearance, approach, or departure, air traffic controllers generally process these requests in the order they are received. However, the nature of air traffic operations allows for exceptions; for instance, priority may be given to emergency situations or certain operational needs that demand immediate attention. This flexibility in service provision ensures that safety and efficiency are maintained, allowing controllers to manage air traffic effectively while still adhering to requests as much as possible.

The other options do not accurately reflect the complexity of air traffic control service provision. While it may seem straightforward to suggest that air traffic control is always first-come, that does not account for the nuances involved in handling diverse flight scenarios and emergencies.