A VCA occurs when a pilot enters controlled airspace without a clearance. Controlled airspace is a section of airspace surrounding an airport with a tower, and/or airspace up to a certain altitude overlying Australia. This airspace may or may not be radar monitored. The controller needs to be aware of all aircraft within hisher section of controlled airspace so as to provide a complete traffic service. Pilots are required to request a clearance before entering the airspace.