What happened
On the evening of December 4, 1998, a loss of separation occurred between two aircraft operating under radar control near Auckland Airport. An Air New Zealand Boeing 767 was departing Auckland and climbing toward flight level 250 while intercepting the Auckland to Rarotonga track. Simultaneously, a Sunair Piper Aztec was transiting from Hamilton to Whangarei, maintaining an altitude of 7,000 feet.
As the two aircraft approached one another, the pilot of the Piper Aztec observed the Boeing 767 closing in from the left side. To prevent a collision, the pilot of the smaller aircraft initiated a descent. Despite this maneuver, the aircraft passed within approximately 0.7 nautical miles of each other horizontally and 900 feet vertically.
The investigation
Investigators examined the actions of air traffic controllers and the performance of automated alert systems during the incident. The investigation established that while the controller was clearing the Boeing 767 to turn right onto its assigned track, they failed to identify the potential conflict with the Piper Aztec flying overhead. However, a recently implemented Short Term Conflict Alert (STCA) system successfully detected the breach of separation and alerted the controller to take immediate collision avoidance measures.
Findings
Several contributing factors were identified regarding the management of the airspace. A primary issue was the controller's failure to notice the conflict with the overflying aircraft while managing the departure. The investigation also highlighted broader systemic challenges, including:
- Difficulties faced by controllers in maintaining situational awareness regarding aircraft flying at higher altitudes over a sector.
- Inconsistencies in how flight progress strips were managed.
- The increased span of responsibility for controllers following the consolidation of air traffic control sectors.
- Complexities in the interaction between ground-based Short Term Conflict Alert systems and airborne Traffic Alert and Collision Avoidance Systems (TCAS).
- A specific instance where a controller's transmission to aircraft SAV 17R was interrupted.