A Beech 200 was conducting an instrument flight rules (IFR)
flight from Lismore to Glen Innes. The pilot gave a departure
report to the Brisbane Sector 2 radar controller, and reported
climbing through 3,500 ft. The controller advised that there were
no other aircraft observed on the radar display. That departure
report was also heard by the crew of an IFR Saab SF-340 that had
just departed Casino on a flight to Williamtown, via Point Lookout.
The Saab was climbing through 2,700 ft when the crew became aware
that both aircraft were approximately 5 NM south-west of Lismore.
The Saab crew descended to 2,500 ft, in order to establish 1,000 ft
vertical separation from the Beech. The Saab crew subsequently saw
the Beech pass from left to right, about 1 NM in front of their
aircraft, as the Beech climbed through patches of cloud just under
the main cloud base of 4,000 ft. The Beech pilot also saw the Saab
pass below his aircraft.
Due to their proximity to each other, Lismore, Ballina and
Casino aerodromes were encompassed by a non-standard Mandatory
Broadcast Zone (MBZ), and used a common radio frequency of 124.2
MHz. The MBZ was approximately 60 NM long and 30 NM wide, and
extended from the ground to 5,000 ft above ground level. The intent
of the common frequency was to enable pilots operating at any of
those aerodromes to hear transmissions from other pilots, so that
they could coordinate operations in order to minimise the risk of
conflict. Pilots were required to monitor the MBZ frequency when
operating within the MBZ. They were also required to broadcast
flight details when inbound to, taxiing at, and departing from an
aerodrome within the MBZ.
The pilots of both aircraft had made the required broadcasts;
however, neither received a response from any other aircraft. While
taxiing at Lismore, the Beech pilot had monitored a transmission on
the MBZ frequency from another pilot, but disregarded it as that
aircraft was operating in the Ballina area. A recording device was
installed at Lismore aerodrome to monitor aircraft using that
facility. The majority of recorded transmissions from aircraft
operating at Lismore were clear. Transmissions recorded from
aircraft operating at Ballina and Casino were generally clipped or
garbled, and more difficult to understand. The Saab crew later
reported that pilots of aircraft on the ground at Lismore were
unlikely to hear radio transmissions from aircraft on the ground at
Casino, and vice versa.
At the time of the occurrence, both aircraft were operating in
non-controlled Class G demonstration airspace. As part of that
demonstration, modified procedures had been introduced, including
the removal of the directed traffic information service previously
provided by flight service, and the introduction of a radar
information service provided by air traffic control. The provision
of that service to pilots was dependent upon their aircraft being
radar-identified. The secondary surveillance radar code from the
Beech was not detected by the air traffic control radar system
until it had climbed through an altitude of 3,300 ft. The Saab was
not detected until it had climbed through approximately 3,000
ft.
Prior to the commencement of the demonstration, pilots of IFR
aircraft were provided with traffic information on other IFR
aircraft, in accordance with guidelines detailed in the Manual of
Air Traffic Services and the Aeronautical Information Publication.
Pilots operating an IFR flight from a non-controlled aerodrome were
required to contact flight service by radio when taxiing. A flight
service officer would then provide traffic information to pilots of
conflicting aircraft that were not on the MBZ frequency. Based on
that procedure, the Saab crew and Beech pilot would not have been
provided with mutual traffic information, as they were both
operating on the MBZ frequency at about the same time. However,
traffic information was required to be passed to pilots of IFR
aircraft climbing or descending through the level of another
conflicting IFR aircraft. The overriding intent of the traffic
information service was to issue such information if there was any
doubt regarding the possibility of a confliction.
The Beech pilot had requested radar service information from air
traffic control while taxiing at Lismore. The controller issued the
pilot with a secondary surveillance code for the flight and advised
that a radar information service would be provided when the
aircraft was identified on radar, and that there were no other
aircraft observed in the area.
Both aircraft were fitted with dual very high frequency (VHF)
radio transmitters and receivers. The pilots were monitoring the
MBZ frequency on one receiver while also monitoring the air traffic
control frequency on the second receiver, in preparation for
requesting a clearance to enter Class E controlled airspace at
8,500 ft. The Beech pilot stated that he normally would not have
monitored the air traffic control frequency until passing 4,000 ft,
but decided to contact the controller early to request the radar
information service. Prior to the commencement of the demonstration
period, pilots would normally have simultaneously monitored the MBZ
and flight service area frequencies to assist in maintaining their
situational awareness during the departure phase.
