Clearance must be obtained before an aircraft enters controlled airspace according to the rule of Air. All aircraft wishing to do so must file a flight plan, either on the ground before flight, or in the air. The air traffic services involved must receive the request at least 10 minutes before the expected time of entry.
A pilot wishing to enter controlled airspace should call the ATC responsible for the controlled airspace concerned using the frequency specified in the AIP or Flight Guide. The initial call should be made at least 10 minutes before entering, and should consist of the aircraft call sign followed by a brief statement of the request. The control tower is responsible for transmitting departure clearance to IFR flights. Penetration of restricted areas without authorization from the using or controlling agency may be extremely hazardous to the aircraft and its occupants. ATC facilities apply the following procedures when aircraft are operating under an IFR clearance via a route which lies within joint route-use restricted airspace. This is only if the restricted area is not active and has been released by the FAA. If the restricted area is active and has not been released to the FAA, the ATC facility issues a clearance which ensures the aircraft to avoid the restricted airspace.