What is a restricted area in aviation?

A restricted area in aviation is defined as an airspace where operations are hazardous to non-participating aircraft, which is why option B is the correct choice. These areas are established to protect both the aircraft conducting activities—such as military operations or testing—and other aircraft that might inadvertently enter the area.

Pilots must have specific clearance to enter a restricted area, typically for safety reasons, as activities in these areas could include live ordnance testing, military exercises, or other operations that pose risks to general aviation traffic. This also distinguishes restricted areas from prohibited areas, which are entirely off-limits to all aircraft without exception, and from areas designated solely for emergency landings, which serve a different purpose altogether. Additionally, while areas with heavy commercial air traffic may require specific attention and management, they do not specifically fit the definition of a restricted area concerned with the safety of non-participating aircraft.