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.