On 26 July 1999, an ATR 72-200 being operated by Mount Cook Airlines on a scheduled passenger flight from Christchurch to Queenstown entered the destination CTR without the required ATC clearance after earlier cancelling Instrument Flight Rules (IFR) and in marginal day Visual Meteorological Conditions (VMC) due to snow showers, separation was then lost against a Boeing 737-200 being operated IFR by Air New Zealand on a scheduled passenger flight from Auckland to Queenstown which was manoeuvring visually (circling) after making an offset VOR/DME approach in accordance with a valid ATC clearance.
An Investigation was carried out by the New Zealand Transport Accident Investigation Commission (TAIC). An annotated terrain chart taken from the official report is shown below to aid an understanding of the conflict which occurred.
Queenstown Visual Terminal Chart effective 15 July 1999 (not to scale)
It was established that the ATR 72 had cancelled IFR and descended below controlled airspace in order to remain in VMC and was tracking via the Kawarau Gorge at low-level. Before entering the gorge, the ATR 72 had been advised by ATC of a possible requirement to hold at the Bungy Bridge VRP on the edge of the CTR but having committed to fly through the gorge in deteriorating weather, the ATR 72 was then unable to hold at the reporting point when instructed to do so and advised their alternative intention. They subsequently stated that they had continued through the gorge visually in the belief that they did not need to obtain an entry clearance into the CTR.
The Boeing 737 had made an approach on the prescribed track inbound to the VOR of 260° in accordance with an IFR clearance and become visual with the runway about 4nm prior to reaching the VOR. It had advised circling to the right in order to position from the south west onto finals for the landing Runway 23. It was concluded that since ATC had initially been unsure of the location and intended flight path of the manoeuvring Boeing 737, by the time both aircraft were coming into proximity in the CTR at the same time, they had been left with little option but to advise the ATR 72 to position on finals ahead of the Boeing 737. The effect of this action was that the Boeing 737 was then committed to continuing towards the airport in reducing visibility because the ATR 72 had obstructed its primary missed approach option to the south of the airport. The ATR72 landed first followed about one minute later by the Boeing 737 with IFV estimated by the Commander of the Boeing 737 to have been about 3000 metres. It was established that at no stage had either aircraft seen the other whilst within the CTR.
It was determined as a result of the Investigation that:
- Safety procedures for flying VFR through Kawarau Gorge were inadequate
- There appeared to be a generally poor industry understanding of the requirements for flight SVFR.
- Position reporting by aircraft becoming visual on the Christchurch instrument approach involved were inadequate.
- There were unresolved issues related to flight under VFR by medium and large air transport aircraft.
- There was poor industry understanding of the management of general aviation areas within the Queenstown CTR
It was concluded that the incident stemmed from 6 proximate causes:
- The ATR 72 not obtaining an entry clearance from Queenstown Tower before being committed to entering the CTR
- The crew of the ATR 72 assuming that they had automatic clearance to enter the CTR unless specifically told by Queenstown Tower that they did not
- The aerodrome controller’s loss of situational awareness concerning the progress of the two aircraft involved in the incident
- The aerodrome controller’s late request for the ATR 72 to hold clear of the CTR
- the flight crew of the ATR 72 assuming, on the basis of incomplete information, that the Boeing 737 would be clear having either completed the instrument approach or, as they thought more probable, commenced a missed approach
- the foreseeable rapid approach of a snow-shower resulting in a significant reduction in visibility in the vicinity of Queenstown Aerodrome.
Other latent factors considered likely to have precipitated the incident were:
- Mount Cook Airlines’ policy of encouraging pilots to cancel IFR flight and join an aerodrome under VFR whenever possible
- the lack of standardised procedures for the co-ordination of aircraft transiting Kawarau Gorge
- the lack of specified weather and aircraft minima for VFR flight through Kawarau Gorge by Mount Cook Airline aircraft
- a lack of understanding by the pilots of the ATR 72 of the objectives and requirements of operations under special VFR.
Eleven Safety Recommendations were made as a result of the Investigation that:
- Mount Cook Airlines instruct company pilots of the requirement to obtain an entry clearance from the relevant controlling authority before entering controlled airspace (088/99)
- Mount Cook Airlines review company procedures for flights through Kawarau Gorge, including the need for specified minimum flight altitudes and visibility requirements, which permit safe manoeuvring within the geographical constraints of the gorge (087/99)
- Air New Zealand instruct their pilots of the requirement to make a radio call as soon as possible after becoming visual on an instrument approach and, if practicable, on circling approaches to include the aircraft’s position and intended track to be flown (090/99)
- Airways Corporation (ANSP) should review procedures to ensure that if clearance to enter controlled airspace is not available then appropriate phraseology that correctly conveys that meaning is used, and that instructions requiring a specific action in uncontrolled airspace are not given by ATC (091/99)
- Airways Corporation (ANSP) should review procedures to ensure air traffic service staff undergo proficiency assessments within the prescribed time frame (092/99)
- The Director of Civil Aviation should submit for approval a rule change for flight under visual flight rules in uncontrolled airspace by medium and large air transport aircraft, making reference to aircraft size and manoeuvrability, to ensure adequate safety margins are retained (093/99)
- The Director of Civil Aviation should approach the local air traffic service provider and local User Group to discuss the justification and acceptability of developing standardised procedures for the coordination of aircraft flying through Kawarau Gorge (094/99)
- The Director of Civil Aviation should submit for approval a rule change to special visual flight rules, in particular the application of the 1500 feet cloud ceiling, to remove any ambiguities that may exist (095/99)
- The Director of Civil Aviation should educate pilots about the objectives and application of operations under special visual flight rules (096/99)
- The Director of Civil Aviation should educate pilots on the operation of the use of general aviation areas, in particular those areas within the Queenstown control zone (097/99)
- The Director of Civil Aviation should educate pilots of the requirement to make a radio call when becoming visual on an instrument approach (019/00)
The Final Report of the Investigation was published on 26 May 2000 and may be seen in full at SKYbrary bookshelf: TAIC Report 99-005