What happened
On 20 June 2010, a Boeing 737-800 operated by Pacific Blue was performing a conventional instrument approach into Queenstown Aerodrome. Due to the surrounding mountainous terrain, pilots must perform a circling maneuver to land after reaching the minimum descent altitude of approximately 3,500 feet. Upon reaching this altitude, the crew observed low cloud patches in the basin. While the runway was visible, the cloud cover threatened to obstruct the maneuvers required for a landing on runway 23. Consequently, the pilots notified air traffic control that they intended to attempt a landing on the reciprocal runway, 05.
Simultaneously, a second Boeing 737-800, operated by Qantas, was cleared by the controller to begin an approach behind the Pacific Blue aircraft. The Qantas crew was utilizing 'required navigation performance' technology, which permits much lower descent altitudes. The controller permitted this approach under the assumption that the Pacific Blue aircraft would either land or remain within the visual circuit. However, the Pacific Blue crew, unable to maintain visual contact with runway 05 due to the cloud, abandoned the circling maneuver and climbed directly to intercept the missed approach track. This climb, necessitated by the proximity of terrain, deviated from the controller's expectations. To maintain separation, the controller subsequently ordered the Qantas aircraft to perform a missed approach at a maximum rate of climb.
The investigation
The investigation focused on the high potential for a vertical separation breach between the two aircraft. Because the Queenstown tower lacks radar capabilities due to local topography, the investigation centered on the procedural and communicative failures between the cockpit and the tower. The Commission examined the compatibility of the different approach technologies in use, the accuracy of published aeronautical information, and the adequacy of the air traffic management system for the increasing volume of jet traffic at the aerelodrome.