What happened
On December 17, 2015, a series of traffic management failures occurred at the Hamilton aerodrome control tower during an annual proficiency assessment of an aerodrome controller. While the tower was managing a high volume of traffic, the controller experienced a breakdown in situational awareness, leading to four distinct incidents.
The most critical event occurred when the controller directed two aircraft onto a head-on, converging path. The aircraft involved were a Diamond DA42 Twin Star performing an instrument approach and a Diamond DA2 .20 Katana operated by a pilot on their first solo flight. Both aircraft were on the final leg of the circuit pattern, approximately 600 feet above the ground, when they realized the conflict and maneuvered to avoid a collision. The aircraft ultimately passed within 0.5 nm of each other. Following this fourth incident, the assessor intervened and took over air traffic control duties to stabilize the situation. No injuries or collisions were reported.
The investigation
The Transport Accident Investigation Commission (TAIC) examined the operational environment and the human performance factors involved in the incidents. The investigation focused on the controller's management of the mixed flow of instrument flight rules (IFR) and visual flight rules (VFR) traffic during a period of high activity.
Investigators looked into the circumstances of the proficiency assessment, specifically how the presence of an assessor and the lack of a formal pre-assessment briefing influenced the team's performance. The inquiry also reviewed the broader staffing practices of Airways Corporation of New Zealand Limited, specifically the practice of assigning recently qualified controllers with limited experience to the high-traffic Hamilton unit.
Findings
- The controller became overwhelmed by the high traffic volume, resulting in a loss of situational awareness regarding aircraft positions within the control zone.
- The standard of team resource management within the tower did not meet industry best practices.
- The required briefing procedure prior to the proficiency assessment was not fully executed, which negatively impacted team dynamics.
- The practice of posting inexperienced controllers to a busy aerodrome like Hamilton increased the overall risk profile of the unit.
- There was evidence of "over-controlling" VFR traffic, where excessive radio communications unnecessarily congested the frequency and created difficulties for pilots, particularly those with English as a second language.
- Changes to the Hamilton control zone boundaries had inadvertently shifted traffic congestion to areas outside the zone, increasing collision risks in those locations.
Safety action
Following the incidents, Airways implemented a mentoring system for controllers at Hamilton and introduced a "Coaching on the Go" course to improve professional standards. The commission also noted that the CAA has since revised the Hamilton airspace boundaries to mitigate congestion. To address radio congestion, the commission emphasized the necessity of clear and succinct communication between controllers and pilots.