For over 90 years of aviation, QANTAS has been at the forefront of numerous technological advances. From the dawn of the jet age and the Boeing 707 to the certification of the Future Air Navigation System (FANS) was in 1995. Today the airline is once again at the cutting edge with advanced navigation development. Nowhere is this more evident than in its challenging operations into New Zealand’s Queenstown Airport where the latest technology has their Boeing 737-800s setting the pace.
A Remarkable Place.
As destinations go, they don’t come much more dramatic or scenic than Queenstown, New Zealand. The mountain range known as The Remarkables tower 7,500 feet above sea level and along with the surrounding peaks draw ski enthusiasts from around the globe. But there is more to the region’s beauty than its seasonal white blanket of snow. On a clear day, its dramatic peaks reflect in the glassy surface of Lake Wakatipu and it is easy to see why it was found suitable as the mythical “Middle Earth” in filming “The Lord of the Rings”.
It is undoubtedly one of the most beautiful areas around which to fly and this is further evidenced by the amazing amount of general aviation traffic that operates from the airport and the surrounding waterways. There are aerobatic joy-flights, parachute operations, scenic journeys to the nearby Milford Sound, heli-skiing and so much more, giving the region a distinct sense of aviation. Yet the location of Queenstown Airport (NZQN) is not what one may regard as geographically ideal for aviation.
The airport effectively sits in a natural bowl, surrounded by peaks and ridge lines. The terrain is not the only challenging aspect as the winds that swirl around the basin can vary significantly in both speed and direction at different levels. Even on a crystal clear day, the combination of traffic and terrain can make manoeuvring an airline category aircraft challenging, so any deterioration of weather conditions further contributes to the demands of making an approach or departure.
The airfield has long been serviced by traditional non-precision approaches and specific visual procedures; however they are less than ideal. The absence of vertical path guidance is one factor, while the inability to align the approaches with the runway or achieve an effective instrument approach are others.
At the bottom end of the instrument approach, the runway is 30 metres wide and a touch under 1800 metres in length, effectively limiting the port to operations by Boeing 737s and Airbus A320s. While a very proficient control tower is operational, there is no radar coverage, further increasing the tolerances required for procedural separation. However, in the near future, a Wide Area Multilateration system will be introduced to aid situational awareness.
In so many ways, operations to and from Queenstown can present a variety of challenges to crews. As a destination the enhanced safety and efficiency on offer through RNP operations elevated the profile of the South Island ski resort in the aviation world. If RNP could be proven to work here, then its overall potential and credibility could only grow.
The Right Approach.
RNP approaches dispense with the limiting rigid straight lines, arcs and trapezoidal obstacle clearance of traditional instrument approaches and departures. By maintaining an ‘area of containment’ relative to the designed track, it is possible to permit optimised routing, clear of terrain, noise sensitive areas and high density airspace.
In the case of Queenstown, terrain is the limiting factor. While the challenges of terrain are obvious, operationally it makes the design of conventional VOR approaches and departure procedures a very challenging task and this equates to higher instrument approach minimas. Higher minimas in turn equate to a lowered assurance of being able to become visual when weather descends upon the airfield and this impacts directly upon the commercial reliability of the service.
For example, the best case scenario for a traditional VOR approach minima into Queenstown is 4,600’ or around 3,400’ AGL. In comparison, the RNP-AR 0.1 onto Runway 05 as pioneered by QANTAS can achieve a minimum altitude of 1451’, or a mere 291’ AGL. Furthermore, the RNP-AR approaches establish the aircraft on final, stable and aligned with the runway. By comparison, the VOR approach still calls for some challenging manoeuvring within the basin to ultimately achieve a landing as the approach leaves the aircraft well above profile to effect a straight-in landing.
Similarly, on departure, the RNP calls for a minimum cloud base 300’, while the old-style departure tracks require a 4000’ ceiling or greater. Like the arrival, the departure provides both lateral and vertical guidance to maintain the aircraft within its safe area of containment as it climbs to achieve the minimum safe altitude (MSALT) of 10,600’ within 15 miles.
Even so, there are RNP approaches and there are RNP-AR approaches. The former are generic approaches designed under the limitations of PANS-OPS Doc 9905, while the latter ‘Authorisation-Required’ tailored approaches are designed by GE/Naverus in conjunction with QANTAS. However, both containing the critical element of vertical path guidance and position the aircraft favourably to conduct a landing. However, the improvements are not merely at the minimum altitudes, as the vertical path guidance offered by RNP approaches is also a significant safety enhancement.
At Queenstown, safety is also enhanced through RNP by the precise ‘engine-out’ procedures on offer. In the event of either an engine failure on departure, or a single-engine missed approach, the RNP offers a safe resolution despite the challenges of the surrounding terrain. The complex tracking is automatically availed to the crew through the FMC when the engine fails. They need only execute the modified routing and continue to fly the aircraft along the new track, ensuring containment at all times. As with normal RNP operations, judicious use of the autopilot provides the best means of ensuring flight within the specified tolerances, while managing the aircraft’s flight-path and configuration. So much so, that its use is not simply preferred, but required beyond certain points on the approach and departure.
In the face of challenging conditions, the growth of RNP operations into Queenstown has offered not only greater schedule reliability, but an enhanced level of safety. Even so, nothing is ever taken for granted and all QANTAS aircraft operating to Queenstown are required to carry an alternate, regardless of the weather. Even with the best technology, aviation is a dynamic environment......
Check back for the conclusion of Queenstown. The Remarkable Challenge of RNP.
This article first appeared in Australian Aviation Magazine.