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 his/her section of controlled airspace so as to provide a complete traffic service. Pilots are required to request a clearance before entering the airspace.