What happened
On the afternoon of Monday, 2 June 1997, two aircraft traveling in opposite directions experienced a loss of separation while operating on the track between Hamilton and Taumarunui. The first aircraft, an RNZAF Hercules, was flying northbound when the crew reported experiencing difficulties with aircraft pressurization. In response to this issue, the Area Controller instructed the RNZAF Hercules to descend from flight level 170 to 10,000 feet.
During this maneuver, the RNZAF Hercules passed in close proximity to an Eagle Air Metroliner traveling southbound. The two aircraft maintained a horizontal distance of approximately 0.7 nautical miles and a vertical separation of only 600 feet.
The investigation
The investigation focused on the radar control environment and the specific instructions provided to the flight crews. Investigators examined the actions of the Area Controller and the adherence to established separation standards. The inquiry confirmed that the aircraft were under active radar control at the time of the incident.
Findings
The investigation found that there were no failures in the application of standard radar control procedures. However, the incident highlighted a critical vulnerability in the existing monitoring capabilities. The primary factor contributing to the risk was the lack of an automated on-screen alert to notify controllers of an impending loss of separation. The findings emphasized that maintaining separation standards relies heavily on the controller's ability to manually monitor both the track and the vertical profile of aircraft.