Which entity is primarily responsible for issuing traffic alerts to pilots?

Air Traffic Control (ATC) is the primary entity responsible for issuing traffic alerts to pilots. This role involves monitoring the movement of aircraft within controlled airspace and providing information to pilots to ensure safe separation and efficient traffic flow. ATC's responsibilities include advising pilots of nearby traffic, changes in weather conditions, and other relevant information that may affect flight safety. By maintaining communication with pilots and managing the flow of air traffic, ATC plays a crucial role in enhancing safety in aviation.

The other options, while related to aviation safety and operations, do not have the primary responsibility for issuing traffic alerts. The National Transportation Safety Board (NTSB) focuses on investigating accidents and promoting safety recommendations after incidents occur. Commercial airlines primarily manage their own flight operations and ensure the safety of their passengers but do not issue traffic alerts to other aircraft. The airport authority oversees the operations of the airport facilities and does not have the authority or function to issue traffic alerts to pilots in flight. Thus, Air Traffic Control is the correct answer for the entity that actively issues traffic alerts to pilots.