In the airspace blocking procedure, what does AOBXXX represent?

AOBXXX stands for "Above Onboard" followed by a specific altitude, typically represented in hundreds of feet. This notation is used in air traffic control to indicate the upper altitude limit of a blocked airspace. For example, if the blocking procedure specifies AOB270, it means the airspace is blocked up to an altitude of 27,000 feet. This is crucial for ensuring that air traffic controllers and pilots are aware of the vertical limits of restricted airspace, allowing for safe and effective management of aircraft operations within and around the blocked airspace.

Understanding this concept is essential for maintaining the safety and efficiency of air traffic management, as it directly influences the routing and altitude assignments of aircraft in the vicinity of the blocked airspace. The other options pertain to different aspects of air traffic control procedures, but AOBXXX specifically designates altitude, making it the correct choice in this context.