Taxi Sequence and Distractions
The incident occurred as a DHC-8 taxied immediately ahead of another aircraft, designated VNC. While VNC had pushed back first, the DHC-8 flight crew had received their taxi clearance and commenced taxiing before VNC. There was no specific instruction for the flight crew of VNC to follow the DHC-8. As VNC followed the DHC-8 to taxiway B4, the flight crew may have been distracted by this following task.
Cabin Readiness and Captain's Focus
As the first officer turned VNC onto taxiway B4, the captain's attention was on communicating with the cabin crew and observing their positions via the cabin video. One item on the pre-take-off checklist (above the line) is 'cabin ready'. The captain, as pilot monitoring, temporarily handed over ATC communication responsibility to the first officer (pilot flying) to confirm cabin status. Because the captain had not heard the initial indication that the cabin was ready, they looked at the cabin video to check the cabin crew were seated and called them on the interphone, who confirmed the cabin was secure for take-off. The captain then resumed ATC communications and returned focus to cockpit activities. As the captain was busy liaising with the cabin crew during the turn onto B4, the likelihood that they would notice the aircraft was approaching the runway on the incorrect taxiway was reduced.
Training Flight and Experience
The first officer had completed 11 sectors and was under the supervision of a training captain. The first officer assessed their workload as moderate. This was the first officer's second flight into Cairns since joining the operator. The captain noted that runway 33 was not the usual runway in use at Cairns due to prevailing winds. A lack of familiarity with the runway may have reduced the flight crew's ability to detect the incorrect runway position when the aircraft was lined up. The captain commented that the first officer was taxiing slightly faster than optimal approaching the holding point. The captain may have been focused on monitoring the aircraft to ensure it stopped before the holding line, which may have distracted them from noticing the B4 taxiway sign to the left of the taxiway. Normally, the pilot flying would complete the flight controls check earlier in the taxi, but the first officer completed it as the aircraft approached the turn onto B4. The captain stated that all checks were completed correctly and in the correct order, but slightly later than normal due to the relative inexperience of the pilot flying.
Pre-Take-Off Checklist and Potential Overrun
The relevant 'below the line' check to confirm the aircraft was prepared for take-off on the correct runway required the pilot flying to state 'runway 33 confirm', then the pilot monitoring to respond 'runway 33 confirm'. While this item confirmed the runway, reference to an intersection was not part of the verbal check. The first officer commented that confirming the intersection as well as the runway during the pre-take-off checks may prevent a similar incident. The aircraft operator reviewed the ramifications of a departure from the B4 intersection using B5 performance take-off data. Initial calculations showed that in the event of a rejected take-off, either with all engines operating or one engine inoperative, would have resulted in a runway overrun.