The pilots of two MIG-15 aircraft were undertaking a series of flights during which passengers could experience simulated aerial combat manoeuvres. The flying was conducted in military restricted airspace to the north of Edinburgh, designated R265A and R265B. Transit flights between Adelaide airport and the airwork area were undertaken as a formation because only one of the aircraft was transponder equipped. The formation used the radio callsign ATLAS for their communications with ATC and the individual aircraft identifications ATLAS ONE and ATLAS TWO.
Flying as a formation, the pilots were cleared to depart the military training area R265A on a heading of 200 degrees and instructed to maintain 8,000 ft. The controller reported that the pilot of ATLAS ONE was heard to instruct the other pilot to descend below 8,000 ft. The pilot of ATLAS ONE then followed the other aircraft below the assigned level. The aircraft descended through controlled airspace and into the Parafield training areas. There was no infringement of separation standards.
The pilot of ATLAS ONE, who was handling the radio communication for the formation subsequently reported that he had lost sight of ATLAS TWO while manoeuvring to formate on it. He instructed the pilot to descend to 6,000 ft and then to 5,000 ft. He then descended to accompany the other aircraft in a stream formation. He stated that this manoeuvre was based on a military formation break procedure, a practice that they had adopted for the operation of their aircraft when either pilot was unable to sight the other aircraft.
Controllers had not been made aware of the possibility of the need for a formation break manoeuvre and were not familiar with any formation break procedures for the MIG-15 aircraft. The Manual of Air Traffic Services made reference only to military formation flights. It stated that when a formation break was likely to be required, the military authority was responsible for making suitable arrangements with air traffic services to ensure that any formation break procedure could be employed without compromising the safety of other traffic within controlled airspace.
The MIG-15 aircraft were civil registered and operated as Limited Category aircraft under the provisions of Civil Aviation Regulation 262AM that imposed restrictions on the use and operation of these aircraft. However, the regulations did not require the pilots of these aircraft to advise air traffic services, before flight, of any special requirements or conditional aspects of their proposed operations within controlled airspace.
The controller had appropriately issued a clearance that provided the formation with separation from other aircraft. However, without the knowledge that the aircraft may require additional airspace for an abnormal manoeuvre, the controller was unable to apply procedures to provide separation assurance. The reason why the pilots did not recognise that by descending without a clearance they created a potential traffic conflict, could not be established.