Final answer:
Blue hash marks on a VFR sectional chart signify controlled airspace (option 3) , which is an area where air traffic control manages aircraft operations. Pilots need to communicate with ATC to enter such areas, which are marked for safety and efficient traffic flow.
Step-by-step explanation:
On a VFR sectional chart, blue hash marks indicate controlled airspace. These marks outline specific areas of the sky where air traffic control (ATC) has the authority to control aircraft operations. This means that pilots must establish communication with ATC to gain clearance to enter, transit, or fly within these zones. The airspace is designed to ensure safe traffic flow among the diverse aircraft that may be flying in the vicinity, such as commercial, military, or private planes.
Controlled airspace is typically categorized into various classes, designated from Class A through Class G, with different rules and requirements. It's important for pilots to understand their responsibilities and the communication requirements when operating in controlled airspace. Blue hash marks on the sectional chart help pilots easily identify where these areas are and plan their flights accordingly.