On 21 April 2006, the crew of a Boeing 737-800 (VH-VXS) being operated on a scheduled passenger flight from Brisbane to Mount Isa in normal ground visibility and daylight commenced take off in accordance with their issued clearance and then observed a vehicle crossing the runway ahead. Having assessed that it would be clear by the time their aircraft reached the crossing position, they continued and completed the take off with no actual conflict resulting.
An Investigation was carried out by the Australian Transport Safety Bureau (ATSB) into the incident which was classified as an ‘Operational non compliance’. It was established that the 737 had entered runway 01 for take off from taxiway A7 (see the annotated diagram below). A vehicle towing an out of service 737 (Tug 41) was behind the departing 737 at A7. Another vehicle not towing an aircraft, Tug 92, was at the H4 holding point and both vehicles were waiting for clearances to cross the runway which, in accordance with local practice, would be given by the GND controller on the GND frequency. Seven seconds after the TWR controller had issued a take off clearance to the departing 737, the GND controller cleared the Tug 92 to cross the runway (from right to left as viewed by the crew of the departing aircraft) and it began to move.
Shortly afterwards, the 737 began its take off roll with the First Officer as PF. The PF stated that he had first seen ‘something on the runway’ when the aircraft was accelerating through about 50 knots and the PM was ‘head down’ completing the setting of take off thrust. The PM had looked up and had assessed that the vehicle would be clear by the time they reached its position “and at about 80 knots had called ‘continue’ (with) the aircraft about 1200 metres from the vehicle”. Subsequently the vehicle cleared as expected and the aircraft “was airborne prior to reaching (the intersection involved)”. It was noted that the distance between the A7 and H4 intersections was 1418 metres.
It was reported to the Investigation by the ANSP that the GND controller had stated that “at the time of the incident he had ‘formed a mindset or belief’ that the required coordination for both tugs had been completed”, when in fact only the coordination for Tug 41 had been passed to the (TWR controller). The (GND controller) had also indicated at that time that “he had wrongly believed that he had a clearance from the (TWR controller) for both Tug 92 and Tug 41 to cross the runway”. The Investigation did not indentify any specific distraction which might have affected the performance of the GND controller at the time of the incident and the ANSP advised that there was no evidence that fatigue was a factor.
The Tug 92 crew reported that they had been aware of the 737 lined up on the runway when their clearance to cross was issued and had noted that the aircraft was stationary and there was no heat haze visible in the vicinity of the engines. However, as they crossed the runway they observed the heat haze build up behind the 737 and realised that aircraft was rolling. They reported that they had accelerated to clear the runway more quickly and “recalled that they were still within the runway strip, short of the A4 holding point, when the 737 passed behind them airborne”.
The Investigation noted that at the time the Investigation was being conducted, material on the ANSP website included pictorial representations of runway incursions at various airports. The one for Brisbane is reproduced below and shows that between 1 January 2000 and 31 May 2005, there were 17 reported runway incursions at Brisbane with 35% of those incidents involving vehicles alone or vehicles towing aircraft. Three of these incursions were reported as having occurred at the taxiway H4 intersection with runway 01 with all three involving vehicles. The 2004 publication by the ATSB of a Research Report into Australian runway incursions (referenced below) was also noted.
The Investigation sought to examine “possible factors that resulted in an experienced controller providing a clearance for a tug driver to cross an active runway in front of a departing aircraft” given that the controller involved had believed that the required coordination had been completed. It was “considered likely that one or more of the following factors” had led to this erroneous ‘mindset’:
- the (GND controller) did not have any strips or memory prompts relating to vehicles on the runway other than hand-written scratch pad entries
- coordination was not required to be completed on intercom lines, and the required coordination did not include reference to the vehicle callsigns
- callsigns of the two tugs were only distinguished by the two-digit number suffix
- the normal practice was to not coordinate with the ADC for a clearance to cross the runway until it was thought one would become available.
In respect of the decision of the 737 commander to continue the take off, the Investigation concluded that:
“There is insufficient data available to make a thorough assessment with regard to the decision of the 737 crew to continue with their departure, after observing the tug crossing the runway. However, given the good visual conditions, the distances involved and the fact that both pilots had sighted the tug, there is no reason to believe the actions of the crew in continuing the takeoff was inappropriate.”
The Final Report was published on 28 June 2007.