What must pilots do before leaving an assigned frequency?

Before leaving an assigned frequency, pilots must receive clearance from air traffic control. This is crucial for maintaining safety and ensuring that aircraft are sequenced properly in the airspace. Clearance confirms that the pilot has permission to switch frequencies, which is especially important in busy air traffic environments. Receiving this clearance helps to prevent misunderstandings and ensures that the pilot remains in compliance with air traffic instructions.

It's worth noting that notifying the nearest airport, checking in with other pilots, and reporting altitude changes are important communication practices, but they do not specifically address the requirement for pilots to receive clearance before changing frequencies. Therefore, receiving clearance directly relates to ensuring safety and adherence to air traffic control protocols.