What type of clearance is required for a flight to depart?

A flight departing requires an Air Traffic Control Clearance, which is crucial for ensuring safety and regulatory compliance in the National Airspace System (NAS). This clearance is issued by air traffic controllers and grants the pilots permission to taxi, take off, or ascend to a designated altitude.

Receiving this clearance ensures that the airline has coordinated its intentions with ATC and that the airspace is safe and available for use. By obtaining ATC clearance, pilots confirm that their flight plan is approved and all necessary procedures are followed, such as complying with any airspace restrictions or other traffic factors in the vicinity.

While other options mentioned may relate to aspects of flight preparation—like weather verification prior to departure or a flight plan in some contexts—they do not fulfill the formal requirement necessary for a flight to legally take off from the airport. Only the ATC clearance provides the authorization that directly connects the flight operation with air traffic management protocols.