Near miss prompts calls for Queenstown review

Air accident investigators in New Zealand are urging changes to Queenstown Airport’s air traffic management system after two Boeing 737s came within around 300 metres of each other last June.
The Transport Accident Investigation Commission report details an incident where a Pacific Blue jet that was landing flew too close – with 304 metres of vertical separation – to a Qantas aircraft that was also preparing to land.
The report details that on 20 June 2010, a Boeing 737-800 aircraft operated by Pacific Blue was being flown on a conventional instrument approach to Queenstown.
Because of the mountainous terrain, the minimum descent altitude for the conventional instrument approach to Queenstown is around 3500 feet above the airport. The terrain prevents pilots descending straight ahead from the minimum altitude and landing. Instead, they must circle while descending until their aircraft is in a position to land.
When the Pacific Blue aircraft arrived at the minimum descent altitude, the pilots could see lower cloud in the Queenstown basin, but the runway was clear. However, because low cloud patches would have obstructed their manoeuvring to the final approach for runway 23, the pilots reported to air traffic control that they would attempt to land on the reciprocal runway 05.
Meanwhile, the controller had cleared another Boeing 737-800 aircraft operated by Qantas to begin an approach behind Pacific Blue. The Qantas pilots were flying a required navigation performance approach based on global navigation satellite system technology, which allowed them to descend to a much lower minimum altitude.
At the time, Pacific Blue had not applied to the New Zealand Civil Aviation Authority for authorisation to use that technology.
The controller cleared Qantas for its approach based on an expectation that the Pacific Blue pilots, having started circling, would land or, if unable to land, would remain in the visual circuit.
“Lower cloud was likely to have prevented the Pacific Blue pilots maintaining visual contact with runway 05, so they discontinued the circling and climbed directly to intercept the prescribed missed approach track for the instrument procedure they had flown. They had not planned to enter or remain in the visual circuit as the controller had expected and, because of their position when they commenced the climb, probably could not have done so because of their proximity to terrain,” states the report.
The controller then instructed Qantas to conduct the missed approach for its procedure and at the maximum rate of climb, in order to maintain separation from the Pacific Blue aircraft. The Queenstown ATC tower has no radar facility, because the surrounding mountains are incompatible with that.
“The Transport Accident Investigation Commission did not investigate further whether the minimum required 1000 ft vertical separation between the two aeroplanes was breached, because it was clear that the potential for such a breach was high and that alone was a safety issue that needed addressing,” states the report.
The Commission’s key findings:
– the weather conditions were not suitable for Pacific Blue to descend below the minimum descent altitude
– the air traffic controller had not ensured that the required minimum separation would be maintained between the two aircraft.
– the Pacific Blue pilots and the air traffic controller had different understandings of what would occur in the event Pacific Blue did not land after circling
– the various publications used by pilots and controllers that described instrument approach procedures and circling procedures were not consistent, which was a hazard likely to lead to misunderstandings between pilots and air traffic controllers
– the circling manoeuvring that is required after a non-precision approach at Queenstown is a demanding procedure that ought to be reviewed for suitability
– a wider review of the Queenstown air traffic management system and operational procedures would be prudent, given the special features associated with operations at the airport and the increasing number of commercial jet aircraft operations.

1 Comment

  1. If Radar cannot be deploy due to the mountineous nature of the area, the possibility of deploying MLAT (Multilateration) should be considered to prevent such an occurance. I also support the review of the approach proceduces to remove any ambiguity and confusion.

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