Description

On 20 June 2010, a Boeing 737-800 being operated by New Zealand company Pacific Blue AL on a scheduled passenger flight from Auckland to Queenstown lost Instrument Flight Rules (IFR) separation assurance against a Boeing 737-800 being operated by Qantas on a scheduled passenger flight from Sydney to Queenstown whilst both aircraft were flying a go around following successive but different instrument approaches at their shared intended destination. There were no abrupt manoeuvres and none of the respectively 88 and 162 occupants of the two aircraft were injured.

Investigation

An Investigation was carried out by the New Zealand Transport Accident Investigation Commission (TAIC). Whilst the severity of the actual conflict which had occurred could not be defined in detail because of the non radar environment in which it occurred, the Commission determined that a full Investigation was appropriate because of the likelihood that the systemic risk highlighted by the occurrence was significant. It was noted that the air traffic controller on duty at Queenstown throughout the investigated event was under training and being supervised by an instructor.

It was established that in the case of the Pacific Blue aircraft, the commander was designated as PF in accordance with aircraft handling restrictions applicable to all that Company's flights into Queenstown. This aircraft had been cleared by ATC Queenstown for a non precision approach (the VOR/DME ‘ALPHA’ IAP) as a prelude to a circling approach to runway 23. The reported weather at Queenstown included cloud patches at 1000 ft a cloud base at 5000 ft and visibility of 40 kilometres. The pilots reported that they had considered that the conditions were ‘a bit marginal’ and had discussed the published missed approach procedure in case they could not land. However, the controller had earlier indicated twice that they would become visual and should be able to land. Visual contact with the terrain was acquired at about 500 feet above the MDA, which was equivalent to approximately 3500 feet above aerodrome elevation. Upon reaching MDA, the aircraft began an orbit at that altitude whilst the flight crew reassessed the extent of the cloud in relation to their clearance to continue to a landing on runway 23. Subsequently, the aircraft commenced visual reference manoeuvring below MDA but as they passed overhead the field, it became apparent that the low cloud near the 23 threshold was more extensive than they had previously thought. Shortly afterwards, ATC were advised that positioning to runway 05 would now be attempted, although this intention was not confirmed by a formally amended ATC clearance. However, it soon became clear that they were likely to lose visual contact with the runway because of low cloud and they advised ATC that they had commenced a missed approach and were tracking to the designated missed approach holding point to the south west of the airfield. This was acknowledged by the controller who added “for separation, remain visual if able.” When the aircraft replied “we’ll do our best (we are) intercepting the 212 radial” (the published missed approach track),the controller asked the pilot if he could join the figure-of eight circuit, (see the diagram below) but was told that the flight was intercepting the stated radial and was clear of terrain. The Pacific Blue aircraft was able to clear terrain prior to entering Instrument Meteorological Conditions (IMC).

Earlier the Qantas aircraft, which had previously estimated that they would land about 5 minutes after Pacific Blue, had been cleared by Queenstown ATC to descend to 12000 feet on the RNP ZULU approach for runway 23, later amended to the RNP ZULU approach runway 05. The aircraft was instructed to report passing 6000 feet Altimeter Pressure Settings, which the controller anticipated would occur when the aircraft was about 5nm north-north-west of the airfield. Her plan was that if the first aircraft had not landed or had joined the visual circuit by the time the Qantas aircraft made the report, she would instruct it to commence the RNP missed approach procedure which would achieve at least 1000 ft vertical separation between the two aircraft based on her expectation that the first aircraft would be in or joining the figure-of-eight circuit (see the first diagram below) at 4000 feet QNH.

However, when the Pacific Blue aircraft advised that they were commencing the missed approach procedure as depicted on their IAP Plate for the circling manoeuvre, this invalidated the separation 'plan' made by the trainee controller. Nevertheless, she immediately instructed the Qantas flight, still on its RNP,to commence the RNP missed approach at its best rate of climb. The supervising Instructor-Controller then took over from the trainee.

At one point the Pacific Blue aircraft reported observing a target on their Airborne Collision Avoidance System (ACAS) display which appeared to be a couple of miles behind then and 800 to 900 feet higher but neither aircraft received a TCAS TA or TCAS RA during the period of proximity. FDR data from the two aircraft was used during the Investigation to attempt a reconstruction of the relative flight paths in the vicinity of the airfield and the depiction shown in the second diagram below was developed. It shows Qantas descending then flying a climbing figure-of-eight missed approach whilst Pacific Blue tracks away from the overhead climbing. The contemporaneous positions of both aircraft are shown by the two circles.

It was noted that ATC was required to separate IFR flights from other IFR flights in Queenstown air space, which in the absence of radar had to be achieved procedurally. The ANSP ‘Airways’ reported the event as a possible loss of separation caused by the Pacific Blue aircraft “not following the published missed approach procedure” as a result of which controllers were not certain that the minimum separation of 1000 ft had been maintained. It was noted that at the time of the occurrence, Airways had a multilateration surveillance system on trial at Queenstown which although it only showed unverified positions of the two aeroplanes and their altitudes it had “helped the controllers to manage the situation”.

However, the commander of the Pacific Blue aircraft said later that if ATC had instructed them beforehand to fly the figure-of-eight circuit they might have been able to comply, but once they had commenced the missed approach it would have been difficult to turn right without getting too close to terrain. The commander also observed that as his Company was not authorised to make RNP approaches, its pilots did not know all of the RNP procedure positions referred in communications between ATC and Qantas, and so they had been initially concerned that the Qantas aircraft might be on an approach in the opposite direction to the missed approach track they were flying.

After a full review of the context of the event described, the Investigation analysed the evidence in detail. As a preface to this it was noted that “the mountainous terrain and weather associated with Queenstown Aerodrome make aircraft operations there challenging and potentially more hazardous than at most other airports in New Zealand”. It noted that the high minima associated with non precision approach procedures at Queenstown “meant that jet aeroplanes were not guaranteed to complete every approach” but that “recent advances in RNAV systems mean that true ‘all weather’ operations are now available for flights approved to use that technology although both types of approach could be expected to be in use for some time yet. Apart from the basic concern about safe separation between IFR traffic, there was a specific concern that there was a mismatch between the understanding of the Pacific Blue pilots and ATC of what would follow in the event that it was not possible to land off the circling manoeuvre. A series of other safety issues were also defined and reviewed:

• the suitability of the meteorological conditions for the Pacific Blue flight
• the awareness of meteorological conditions (during circling behind the intervening terrain of) Deer Park Hill
• whether Queenstown circling approaches comply with PANS-OPS
• pilot understanding of the design of instrument approach procedures
• the separation of arriving IFR aircraft
• the validity of the figure-8 circuit and its suitability for jet aircraft
• the protection of the missed approach
• the naming of RNAV approaches
• the safety of operations at Queenstown Aerodrome.

The Visual Circuit for large aircraft (reproduced from the Official Report)

On the basis of this analysis, sixteen Findings of the Investigation were listed which collectively represented a comprehensive indictment of prevailing risk assessment in respect of public transport flight operations at Queenstown and are therefore provided here in full:

1. The reported meteorological conditions were acceptable for the Pacific Blue flight to commence the instrument approach, but, because of low cloud behind Deer Park Hill, were not suitable for the flight to have descended below the instrument approach minimum altitude.
2. The inability of air traffic controllers and pilots of aircraft taking off to observe the meteorological conditions behind Deer Park Hill, an area in which pilots must be able to maintain visual contact with terrain, is a safety issue that needs to be resolved.
3. Pilots, particularly those of jet aeroplanes, making non-precision approaches to Queenstown Aerodrome cannot fully meet the PANS-OPS requirements for such approaches because the runway cannot be kept in sight at all times when their aircraft are circling below the minimum descent altitude.
4. The Pacific Blue pilots were forced to fly an escape manoeuvre, but maintained visual contact with terrain until they intercepted the prescribed missed approach track at a point where they were above the procedure minimum height.
5. The incomplete and inaccurate AIP reference to Civil Aviation Rule 91.413(e) was likely a factor in the routine non-compliance with the Rule by pilots making non-precision approaches to Queenstown Aerodrome.
6. The procedure for circling below the minimum descent altitude after an instrument approach to Queenstown Aerodrome needs to be clarified to ensure pilots and controllers are in no doubt as to their respective actions to achieve separation from other traffic.
7. The minimum required separation between the 2 IFR aeroplanes was not assured because the approach clearance issued to Qantas did not allow for a potential communications failure and it was based on the controllers’ shared assumption that Pacific Blue would, without further instruction, remain in the visual circuit in the event of not landing
8. Had the Pacific Blue pilots turned back towards the aerodrome while climbing to the missed approach altitude of 8500 ft, which was possible under PANS-OPS, a more hazardous scenario might have ensued, because Qantas had already been cleared to descend through the same area.
9. Airways [the ANSP] had not clearly explained to operators that it expected large aircraft that did not land at Queenstown after circling to enter the visual aerodrome circuit.
10. The visual circuit procedure put in place by Airways [the ANSP] for large aircraft at Queenstown should have had the approval of the Director because it was intended as a permanent change that introduced or varied right-hand circuits.
11. Had the controllers realised that the low cloud around the aerodrome made the visual circuit unsuitable for a jet aeroplane, they could have protected the missed approach for Pacific Blue by a more positive means, such as not clearing Qantas for its approach until Pacific Blue had landed.
12. The controllers and the pilots of the Pacific Blue aeroplane did not share the same understanding of how the published missed approach would be protected while Pacific Blue was circling. The different texts in the AIP and the Manual of Air Traffic Services at that time contributed to that misunderstanding.
13. Pilots who are not approved for or not familiar with RNAV procedures may not understand radioed position reports that refer to RNAV waypoints. The communication gap that this potentially creates is a safety issue.
14. Although not a factor in this incident, the use of similar titles for different RNAV approach procedures to the same runway is a hazard that could result in an aircraft flying the wrong approach.
15. It is likely that the level of risk (associated) with flight operations at Queenstown Aerodrome has increased because of changes in the variety and intensity of operations.
16. There is no effective means of ensuring that the common operational information and procedures published by certificated organisations for their internal use are accurate and consistent. That deficiency inevitably results in differences that lead to misunderstandings between operational staff, which can compromise the safety of operations.

A number Safety Actions were taken by Airways to address safety issues identified during the Investigation which had they not been taken would have resulted in Safety Recommendations being issued. These were:

• The amendment by ANSP Airways (acting on behalf of the CAA) of the State AIP entry for Queenstown to clarify the direction of turns and the procedure altitudes applicable to figure of eight circuits and amended the chart sub-heading to read “Procedure if aircraft is maintaining visual reference or circling from an instrument approach and unable to land”.

• The amendment by Airways of the Manual of Air Traffic Services and (acting on behalf of the CAA) the State AIP to state more clearly the minimum weather conditions before the missed approach could be protected by instructing a pilot to enter the aerodrome traffic circuit, and the restrictions upon a controller’s use of this procedure. The Manual of Air Traffic Services procedures confirmed that protection of the missed approach should remain in place until an aircraft has landed.

• The Aerodrome section of the State AIP was amended (by the CAA) to include the CAA requirement that pilots of any air transport flight operating to or from Queenstown Aerodrome be qualified for operations there by a comprehensive briefing, a simulator exercise and a minimum of 2 familiarisation flights into and out of the aerodrome.

• Pacific Blue amended its pilot qualification requirements for Queenstown Aerodrome to include initial and recurrent simulator training for First Officers.

Five Safety Recommendations were issued as a result of the Investigation:

• that the Director of Civil Aviation ensure that the strategic plan being developed by [ANSP] Airways and the risk assessment being conducted by the CAA in regard to Queenstown Aerodrome address the following safety issues in respect of that aerodrome and, if applicable, generally:
  • the variability of procedures used by pilots when circling after a non-precision approach and in the event of not landing off an approach
  • the separation of aircraft making different types of instrument approach in Queenstown controlled airspace
  • the appropriateness of the large aircraft visual circuit procedure at Queenstown
  • the naming convention for RNAV procedure waypoints, which makes waypoint recognition difficult for pilots who are not approved for the procedures

[012/12]

• that the Director of Civil Aviation take action, in conjunction with certificated instrument flight procedure service organisations, to eliminate the use of similar procedure titles for different instrument approaches to the same runway

[013/12]

• that the Director of Civil Aviation require non-precision approaches at Queenstown to be re-evaluated to determine whether any rule exemptions or special procedural requirements are necessary to enable safe circling manoeuvres

[014/12]

• that the Director of Civil Aviation ensure that operational material published by document holders and approved by the Director is accurate and consistent across all users and complies with the prescribed relevant standards

[015/12]

• that the Director of Civil Aviation require Airways and the operator of Queenstown Aerodrome to install a system that provides controllers with real-time observations of the weather conditions behind Deer Park Hill

[016/12]

The Final Report was approved for publication by the TAIC on 13 March 2012 and concluded by stating that the “key lessons” from the Investigation were:

• a pilot must not descend below the applicable instrument approach minimum descent altitude unless certain that the conditions are suitable for a landing
• pilots must understand the operational assumptions in the design of instrument approach procedures, and how those assumptions determine the limits of safe manoeuvring
• organisations that re-publish mutually important operational information from authoritative sources must ensure that the information is accurately reproduced so that all users interpret the information correctly and apply it consistently.

Further Reading

• Loss of Separation - ATCO-induced Situations
• Collision Avoidance
• ATCO Actions in Case of Loss of Separation
• Radar Control - Collision Avoidance Concepts
• Situational Awareness