Notable ones include the Flight Restriction Zone (FRZ) encompassing all airspace up to 18,000 feet (5,500 m) within approximately 15 nautical miles (28 km) of Ronald Reagan National Airport around Washington, D.C. Flights within this airspace, while not entirely prohibited, are highly restricted. All pilots flying within the FRZ are required to undergo a background check and fingerprinting. An additional "Special Flight Rules Area" encompassing most of the Baltimore-Washington D.C. metropolitan area requires the filing of a flight plan and communication with air traffic control.