When issuing clearance, what must always be stated?

The requirement to always state the assigned altitude when issuing clearance is grounded in the necessity for clarity and safety in air traffic control operations. This specific information is critical as it directly relates to aircraft separation and the management of airspace. By specifying the assigned altitude, air traffic controllers ensure that pilots have a clear understanding of their vertical positioning in reference to other aircraft and navigational protocols.

Having an established assigned altitude helps prevent conflicts between aircraft while they are on their departure or approach phases, contributing to overall safety in the skies. This altitude clearance aids pilots in maintaining safe flight paths and complying with air traffic control instructions, thereby enhancing both situational awareness and operational efficiency.

Flight plan details, departure time, and weather conditions, while important pieces of information, do not need to be stated in every clearance communication. Consequently, the focus on the assigned altitude serves as a fundamental aspect of clearance delivery, emphasizing its role in air traffic control protocols.