Boeing Co 737-377 , VH-CZC

As a result of the investigation, Airservices Australia have:
Designed a new runway 15 SWIFT standard instrument departure to
minimise the possibility of conflict in similar circumstances. This
procedure is scheduled for publication on 24 February 2000; and
Initiated regular discussion sessions amongst Cairns air traffic
controllers to, among other things, review techniques used with
successive departures. The first of these meetings took place on 24
June 1999.

The runway 15 SWIFT standard instrument departure allowed the
possibility of a following aircraft turning inside a preceding
aircraft.
The performance of the B737-400 series aircraft was superior to
that of the B737-300 series aircraft.
The use of minimum departure separation standards was
inappropriate.
The decision of the approach/departures controller to
concentrate on data entry tasks during the departure sequence was
not sound practice.

Controllers at Cairns considered that the aircraft were "like
types" for the purposes of departure standards and neither the
aerodrome controller nor the approach/departures controller
considered increasing the separation requirements specified in
Local Instructions. However, Boeing 737-400 series aircraft are
known to normally out-perform the Boeing 737-300 series.

Separation standards used for consecutive departures allowed
controllers to increase the minimum distance at their discretion.
On this occasion it was not increased and, although the runway
departure standard was not breached, the decision did not allow for
any unexpected manoeuvre by either aircraft. Both crews acted in
accordance with the standard instrument departure and the closure
was the effect of aircraft performance.

The approach/departures controller elected to input data to the
air traffic computer during the departure sequence. Although these
actions were necessary, they were labour intensive and diverted his
attention from the air situation display. They were not urgent and
the decision resulted in the controller not having his full
attention on the relative positions of the aircraft when they first
appeared on the display.

The design of the SWIFT 2 standard instrument departure did not
guarantee separation assurance. Whenever the second aircraft
reached 4,000 ft prior to the first aircraft (whatever the reason)
a reduction in horizontal separation was likely.

VH-CZC, a Boeing 737-300, had taxied at Cairns for departure
from runway 15 bound for Sydney.

VH-TJW, a Boeing 737-400, had taxied after CZC, also for a
departure from runway 15 bound for Brisbane.

Both crews had been cleared via the runway 15 SWIFT 2 standard
instrument departure. That procedure required crews to turn their
aircraft at the earlier of 400 ft or the departure end of the
runway and then track to 030 degrees M until climbing through 4,000
ft. At that point the aircraft should be turned right onto a track
of 170 degrees M to intercept the 139 degrees radial of the Cairns
VOR (VHF navigation aid). The SWIFT 2 standard instrument departure
was designed to counter the limitations of high terrain surrounding
Cairns aerodrome and the tracking requirements of inbound aircraft
from the south and east.

At 0604:15 Eastern Standard Time, the aerodrome controller
coordinated the two planned departures with the approach/departures
controller using the phrase "next CZC followed by TJW". The reply
was "CZC unrestricted, TJW unrestricted". That instruction
authorised the aerodrome controller to allow the takeoffs in
accordance with Cairns Local Instruction TOWER-20, which stated
that the aerodrome controller must ensure that 3 NM separation
between aircraft would exist prior to the second aircraft passing
the upwind end of the runway.

At 0604:48, the crew of CZC was cleared for take-off and at
0606:43, the crew of TJW was cleared for take-off. Radar analysis
showed that both aircraft commenced a left turn at approximately
400 ft at, or about, the departure end of the runway and that the
required 3 NM spacing was achieved.

The approach/departures controller had approved a request for a
change of level from a pilot of an aircraft that had departed
Cairns approximately 7 minutes earlier. After issuing the departure
clearances, the controller commenced the process of making the
change in the air traffic computer; an action that required nine
clicks of the mouse. In order to make this change, the controller
looked away from the air situation display (which was on the main
screen) and used the auxiliary screen to observe the flight plan
window while using the keyboard to input the data.

While the controller was performing the information change task,
the crews of the departing aircraft contacted him as required. The
controller acknowledged the radio broadcasts then returned to the
data input task. He did not continue to check the positional
information on the air situation display. A few moments later, he
glanced at the display and realised that TJW had turned earlier
than CZC and was also out-climbing that aircraft. As he was about
to take corrective action, the controller saw that TJW had climbed
through 4,000 ft and had commenced the right turn onto a heading of
170 degrees M. The manoeuvre had placed TJW on a track inside that
of CZC and led to a rapid reduction of horizontal separation to
less than the required standard of 3 NM. The vertical separation
standard of 1,000 ft had not been achieved at the time. Radar
analysis showed that the aircraft passed 1.7 NM horizontally and
approximately 400 ft vertically apart.

The controller immediately cancelled the standard instrument
departure for TJW and issued the crew with a radar heading of 100
degrees M to ensure that, although separation standards would be
breached, TJW would pass behind CZC. The crew of TJW reported that
they had the other aircraft in sight and monitored their flight
path to ensure that they remained clear of that aircraft. Both
crews subsequently reported that they received a traffic alert and
collision avoidance system (TCAS) advice.

CZC, the B737-300 series aircraft, had taken 1 minute and 56
seconds to reach 4,000 ft whereas TJW, the B737-400 series
aircraft, took only 1 minute and 27 seconds to pass the same
altitude. In addition, the initial opening speed created by the
departure spacing off the runway had reduced to zero within 1
minute and 30 seconds of the departure of TJW.