A Boeing 767-336 (B767) was en route from Sydney to Melbourne
and was maintaining flight level (FL) 350. A Boeing 737-800 (B737)
was en route from Melbourne to Nadi, Fiji, and was also maintaining
FL350. The aircraft were on segregated routes that provided lateral
separation until the crew of the B737 was provided with track
shortening. That decision placed the two aircraft on conflicting
flight paths at the same level. The Eildon Weir/Benalla (ELW/BLA)
sector controllers saw the impending conflict and alerted the
Wollongong/Jervis (WOL/JVS) controller. Both controllers then
issued traffic information and instructions to the crews for
avoiding action. Both crews received Traffic Alert and Collision
Avoidance System (TCAS) Resolution Advisories (RA) and the
controllers received a Short Term Conflict Alert (STCA) from The
Australian Advanced Air Traffic System (TAAATS). The aircraft
passed within 4.8 NM laterally and 800 ft vertically. The required
separation standard was either 5 NM laterally or 2,000 ft
vertically. There was an infringement of separation standards.
The B737 crew had flight planned, and had been initially cleared
to, FL330. That was a standard level for the direction of flight.
Levels were assigned depending on a number of factors including the
track of the aircraft in accordance with the Table of Cruising
levels in the Manual of Air Traffic Services (MATS). Aircraft
operating at altitudes and flight levels in accordance with the
table were considered to be at standard levels, and those operating
at altitudes and levels not in accordance with the tables were
considered to be at non-standard levels. The crew of the B737
subsequently requested, and was assigned, non-standard FL350. At
the time of the level change, both the crew of the B767 and the
crew of the B737 had been issued airways clearances on one-way,
designated air routes that formed a segregated race-track pattern
between Sydney and Melbourne.
The controller responsible for the ELW/BLA sectors was
instructing a student training on the ELW sector. Both were
concentrating on the sequencing and separation of two jet aircraft
in a step descent into Melbourne. A step descent allowed aircraft
to simultaneously descend to vertically separated levels provided
that the higher aircraft was progressively assigned levels that
provided vertical separation with the lower aircraft. The step
descent was occurring in the bottom left quadrant of the
controller's Air Situation Display (ASD). The instructor was
positioned behind and to the left of the student so that he could
readily view the ELW sector and the traffic on the left side of the
ASD. The B767 and the B737 were displayed in the top right quadrant
of the ASD. Once the step descent had been established, the
instructor noticed that the B737 was about to conflict with the
B767. By that time the B737 was within the WOL/JVS combined sector
and the instructor advised the WOL/JVS sector controller that he
would be turning the B737. The student instructed the crew of the
B737 to turn right to avoid the opposite direction B767.
The B737 was within the WOL/JVS control area, but under the
jurisdiction (and control) of the ELW/BLA controller. The
Australian Advanced Air Traffic System Human Machine Interface
(HMI) used different coloured tracks and labels to aid situational
awareness. The track and label colour of the B737 was green to the
ELW/BLA controller, and blue to the WOL/JVS controller. The B737
crew should have been transferred to the WOL/JVS sector prior to
crossing the boundary between those sectors and the ELW/BLA
sectors. Had the transfer been made the track label and symbol
would have been green on the WOL/JVS ASD.
The WOL/JVS controller initiated the amended route clearance for
the B737 at FL350, and verbally coordinated the change with the
ELW/BLA controller. At that time, the southbound B767 was on climb
to FL280. The crew of the B767 contacted the WOL/JVS controller and
was assigned FL350. The amended route for the B737 was direct to
ALLOC, a waypoint located 77NM east-north-east of Sydney.
The workload on the WOL/JVS sectors at the time of the
occurrence was reported by the controller to be low. The controller
was providing a directed traffic information (DTI) service to
military helicopters operating under visual flight rules (VFR) in
class "G" airspace. The provision of DTI to VFR aircraft was
available on request and subject to controller workload.
The WOL/JVS controller reported that the ASD at that console had
recently "been faulted" and found to be outside the acceptable
parameters for contrast. Subsequent to the occurrence, the screen
was again checked and was found to be below acceptable contrast
parameters. The controller reported difficulty distinguishing the
blue track colours from the grey background of the screen; they
appeared faded. A track was blue to indicate that the track was
about to become the responsibility of that controller. Tracks will
appear (in this case) blue to only one console at a time. The same
track symbol and label was a different colour to all other
controllers to indicate the relevance of that track to each control
position.
The WOL/JVS controller stated that a smaller information screen
that was open on the WOL/JVS ASD initially obscured the track
symbol and label of the B737. He had used the route function
available in TAAATS to determine the cleared route of the B737. The
controller also stated that he normally used the text message box
in TAAATS as a visual reminder of potential conflicts. He did not
use the text box on this occasion. He also indicated that he would
have preferred using strips because they better facilitated the
acquisition and maintenance of the traffic picture.
The ELW/BLA instructor commented that the angle of view from
behind and to one side of a student made it difficult to see some
areas of the ASD and to monitor keyboard entries.
