When can an aircraft cross an airway?

An aircraft can cross an airway if it has been given permission by an approach controller. This is because airways are defined routes that aircraft must follow, particularly in controlled airspace, to ensure safety and efficiency in air traffic management. When an aircraft is operating within controlled airspace, the approach controller is responsible for managing the flow of air traffic and ensuring that all aircraft are separated and following the correct protocols for navigation.

In general, clearance from an air traffic controller ensures that the crossing of an airway is conducted safely and in compliance with aviation regulations. It not only maintains separation between aircraft but also adheres to the operational procedures set forth for airspace management. Therefore, this option accurately reflects the regulatory framework guiding aircraft operations in relation to airways.

The other options do not provide the necessary regulatory context. Permission from a flight instructor is not applicable once an aircraft is in flight, as flight instructors are primarily responsible for training rather than active air traffic control. Permitting an aircraft to cross at any time does not adhere to safety protocols needed when it comes to airspace, as it could potentially lead to conflicts with other air traffic. While operating in controlled airspace indicates some level of regulatory oversight, crossing an airway still requires explicit permission from air traffic control to