What happened
On the afternoon of July 26, 1999, a separation conflict occurred within the Queenstown Control Zone involving two commercial aircraft. An Air New Zealand Boeing 737 was performing a circling instrument approach when a Mount Cook ATR 72 entered the controlled airspace without receiving the necessary entry clearance.
The ATR 72 had been flying at a low level through the Kawarau Gorge under visual flight rules (VFR) amidst deteriorating weather conditions. Although air traffic control had previously notified the crew of a potential requirement to hold at a specific reporting point on the edge of the control zone, the crew proceeded through the gorge. Due to the weather and their flight path, the crew was unable to comply with a subsequent instruction to hold. The crew operated under the assumption that an explicit entry clearance into the control zone was not required.
Once both aircraft were within the zone, the controller found themselves managing a situation where the ATR 72 had compromised the established approach of the Boeing 737. To maintain separation, the controller positioned the ATR 72 ahead of the larger aircraft. This maneuver left the captain of the Boeing 737 with no alternative but to continue the approach toward the aerodrome despite reducing visibility, as the ATR 72 had blocked the primary escape route to the south.
The investigation
The investigation focused on the unauthorized entry of the ATR 72 into the control zone and the subsequent loss of separation. Investigators examined the flight paths of both aircraft, the weather conditions in the Kawarau Gorge, and the communication between the air traffic controller and the flight crews. The inquiry established that the crew of the ATR 72 entered the zone without authorization, driven by a misunderstanding of entry requirements and the inability to hold at the edge of the airspace due to terrain and weather.
Findings
- The primary cause of the incident was the unauthorized entry of the ATR 72 into the control zone without an entry clearance.
- The crew of the ATR 72 proceeded through the gorge despite being warned of a potential holding requirement.
- The presence of the ATR 72 obstructed the standard escape route for the Boeing 737, forcing the larger aircraft to continue its approach in poor visibility.
- There were significant gaps in industry-wide understanding regarding flight operations under special visual flight rules and the management of general aviation areas within the Queenstown airspace.
Safety action
The investigation identified several systemic safety issues, including the lack of standardized procedures for flying through the Kawarau Gorge and the need for better position reporting by aircraft once they become visual on an instrument approach. Recommendations were issued to the aircraft operators, the Director of Civil Aviation, and the Chief Executive of Airways Corporation to address these operational deficiencies and improve the management of medium and large transport aircraft operating under VFR.