Under what conditions should an approach clearance be issued?

An approach clearance should be issued after the aircraft is established on a published route or approach because it ensures that the aircraft is properly aligned and following the designated procedures for landing. This is critical for maintaining safety and efficiency in the airspace, as it allows air traffic controllers to manage multiple aircraft while ensuring they adhere to the required flight paths and altitudes.

Issuing an approach clearance at this point confirms that the aircraft is in a position to proceed safely towards the airport and prepares it for further instructions as it continues its descent. The established route or approach includes specific altitudes and navigational aids that guide the aircraft, making it essential for controllers to only issue clearances when the aircraft is correctly on this path.

Communication establishment, the timing of the aircraft's position relative to the runway, and requests for permission are important elements of air traffic management; however, they do not replace the necessity for the aircraft to be established on an appropriate routing before an approach clearance is issued. This procedure is critical for maintaining order in busy airspace and enhancing the safety of flight operations.