Section 21 (2) of the Transport Safety Investigation Act 2003 (TSI Act) empowers the Australian Transport Safety Bureau (ATSB) to discontinue an investigation into a transport safety matter at any time. Section 21 (3) of the TSI Act requires the ATSB to publish a statement setting out the reasons for discontinuing an investigation.
Discontinuation notice of AI-2015-063
Between 2012 and 2017, the ATSB identified Jandakot Airport (Western Australia) as having a disproportionate number and rate per flight of airborne near collisions and other aircraft separation related issues compared with other class-D metropolitan airports. As a result, the ATSB commenced a safety study investigation under the Transport Safety Investigation Act 2003, which aimed to identify the factors that resulted in this apparent increased the collision risk to aircraft operating at Jandakot Airport.
Recent data analysis from July 2017–2019 indicates that this is no longer the case, and this safety study has therefore been discontinued.
The ATSB will continue to monitor issues associated with near collisions and separation issues at Class D metropolitan airports.
Trends at Jandakot Airport
The ATSB initially analysed aircraft separation related occurrences across a 10-year period from 2008 to 2017 in class-D and outside controlled airspace across Australia. Inside the class-D metropolitan airport control zones (3 NM around the aerodrome), all metropolitan airports had a similar rate of separation occurrences in the first years of the study (2008–2012). However, in the second half of the study period (2013–2017), Jandakot Airport had a statistically higher rate of occurrences per 100,000 flights, compared to both the previous five-years (2008–2012) and all other metropolitan airports. However, from July 2017, this higher rate of separation occurrences at Jandakot reduced substantially (Figure 1). Evaluation of occurrences beyond the initial 10-year study range (to the right of the orange line in Figure 1) revealed this lower rate was on par with other metropolitan airports, and has remained so for each six month period since (to June 2019).
The reduction in the rate of separation related occurrences coincided with a 13 per cent reduction in the average number of flights in each 6-month period from July 2017 to June 2019 compared to flights from the previous five years. The number of separation related occurrences reduced by an average 65 per cent each 6 months from July 2017 to June 2019, five times more than the proportional reduction in flights, compared to the average of the previous five years.
Coinciding with the reduction in the number of flights at Jandakot Airport was the suspension of operations of a flight-training organisation from April 2017 at Jandakot Airport. In the five years prior, 25 of the 197 aircraft (about 13%) involved in separation related occurrences (98 occurrences) in the Jandakot class-D control zone were operated by that organisation; similar to the proportional reduction in the total number of flights described above. This suggests that if this particular flight training operator made up about 13 per cent of flights prior to suspending operations, it has been involved in the same proportion of separation related occurrences relative to the number of aircraft they had airborne. Therefore, during their active years, the organisation does not appear to have an over representation of aircraft directly involved in separation related occurrences at Jandakot.
That is, separation related occurrences reduced by five times more than the number of flights after the suspension of operations by a single flight training organisation, although occurrences directly involving that operator were probably were not disproportionately higher. Therefore, it is expected that other systemic factors existed contributing to the elevated rate at Jandakot between 2013 and 2017. It is possible that, in combination with the operational dynamics at the airport, increases in traffic density (the number of aircraft arriving, departing and in the circuit at the same time), at an already busy airport, had a disproportionate impact on the likelihood of a near collision. Additionally, dynamics in the control zone may have changed, through a different proportional mix of operations and aircraft types, such as ab-initio flight training, private and commercial flying. This in turn may have resulted in a reduction in the near collision risk.
The ATSB did not have information relating to the distribution of the types of operations conducted at Jandakot from 2008 to June 2019. However, the highest number of movements were between 2008 and 2012, and this period coincided with a considerably lower occurrence rate at Jandakot. Therefore, future increases in flight movements alone may not result in a disproportionate increase in separation related occurrences. However, it is possible that an increase in flight movements combined with a similar mix of organisations and operational dynamics to those occurring between 2013 and 2017 may result in the airborne collision risk increasing to previous levels at Jandakot Airport.
Based on the reported data, the ATSB also made a number of observations during the analysis.
Pilot awareness of other aircraft
Overall, near collisions where neither pilot was aware of the other aircraft were more likely to involve a closer proximity distance than when at least one pilot was aware of the other aircraft. Consequently, in class-D airspace where air traffic control provide a verbal collision alert to either pilot, the distance between aircraft involved in near collisions were generally further than when no alert was provided.
Near collisions during air traffic control tower operations within the Jandakot Airport control zone were more likely to pass further away than near collisions at Moorabbin (Vic.) and Bankstown (NSW) airports. This was very likely due to a higher proportion of pilots at Jandakot Airport being aware of the other aircraft.
Collisions (class-D and outside controlled airspace)
There were 17 airborne collisions between 2008 and 2017. Almost all occurred at known geographical focal points for the activity conducted. Half involved approach, departure or within the circuit area of an aerodrome, with the other half involved both aircraft conducting the same type of activity (fire bombing, mustering, feral animal culling, gliding). Factors known to mitigate airborne collision risk in these circumstances are maintaining an effective lookout, using flight radio to identify other aircraft and alert other pilots, and implementing formalised strategies to coordinate between aircraft when conducting common operations.
The ATSB did not identify any ongoing safety issues with this analysis. However, the ATSB will brief both the Civil Aviation Safety Authority and Airservices Australia on the detailed analysis to help with future airspace planning.
- Class-D airspace is controlled airspace surrounding general aviation and regional airports equipped with a control tower. All flights require air traffic control clearance to operate in this airspace. Positive separation between aircraft is only provided between IFR and special VFR flights. Traffic information (not separation) is provided to and about VFR flights.
- Class-D metropolitan airports refers to towered airports operating procedurally controlled (class-D) airspace in Australia’s capital cities, specifically, Archerfield Airport (Brisbane), Bankstown Airport (Sydney), Jandakot Airport (Perth), Moorabbin Airport (Melbourne) and Parafield Airport (Adelaide).
|Date:||22 June 2015||Investigation status:||Discontinued|
|State:||Western Australia||Occurrence type:||Separation issue|
|Release date:||26 November 2019||Occurrence category:||Other|