The next step

‘Required Navigation Performance’ technology has brought a great deal to the table. Freed of ground-based navigation aids that require constant maintenance and calibration, RNP looks to the stars and draws upon the precision of satellite-driven GPS accuracy. At destinations where terrain had once precluded the long final leg of precision approaches, RNP now weaves its flexible path clear of mountains and metropolis alike. It is a safe, efficient and neighbourly means to guide aircraft to the runway with the low minimum altitudes that were once solely the domain of the ILS.

Queenstown on New Zealand’s south island is probably best known as the setting for the epic film trilogy, “Lord of the Rings”. With its jagged peaks and twisting valleys it provided the perfect backdrop for the dramatic for the trials and tribulations of ‘Middle Earth’. Far removed from Tolkein’s classic fiction, Queenstown has also provided the ideal arena for RNP to take the stage. Those same jagged hills and ranging valleys that astound with their beauty, are the bane of aviation’s quest for precision approaches. From the flight decks of the Qantas Boeing 737s that pioneered these RNP approaches, to the far flung reaches of the United States Congress, the evolution of RNP in Queenstown has been monitored with great interest. Fundamentally, if it could succeed in such a terrain-rich environment, then it could succeed anywhere. And so it has. Now RNP procedures offer their safety and efficiency at Australian ports ranging from capital cities to Ayers Rock and Broome. But Queenstown was not quite done with RNP just yet.

Queenstown’s Journey.

The first validation flights of RNP approaches at Queenstown date back to July 2004 when the first Boeing 737-800 weaved its way past Bungy Bridge. Such was the interest that aside from the crew of Captains Alex Passerini and Ian Brinkworth from Qantas, the flight was manned by Boeing’s Chief Research Pilot Tom Imrich as well as their former 767 Chief Test Pilot, Buzz Nelson. Along with Captain Steve Fulton, Buzz was now working at Naverus/GE where the approach design had taken place. Representatives from CASA and CAA NZ were also shown the impressive capabilities of RNP prior to formal approval. The rest, as they say, is history.

RNP brought the minimum approach altitude down to around 250 feet above the ground compared to the 4,000 feet on offer by the traditional VOR/DME approach. Along with the lower minima came increased schedule integrity and a runway aligned approach that dispensed with any need for circling proximal to the terrain to lose height and position the aircraft to land. These original RNP approaches continued to evolve into even more efficient ‘Stage II’ approaches whose precision would ultimately become refined down to the highest certified level of RNP 0.1.

The ensuing years saw a significant reduction in weather-related diversions from the often weather-affected Queenstown and progressively other airlines in addition to Qantas adopted the technology until RNP effectively became the norm. Additionally, the precision of the RNP departures, particularly in the critical case of an engine failure at V1, permitted improved payload uplift from Queenstown.

However, what Queenstown possessed in RNP technology it lacked in air traffic separation. Wide Area Multilateration radar offers controllers some degree of situational awareness, but not the ability to separate aircraft. Without full radar coverage to aid air traffic controllers in sequencing the arrivals and departures, rather cumbersome procedural separation standards were employed. While safe, these procedures slowed traffic movements in instrument conditions down to only six arrivals per hour. For an ever-growing tourist destination any measure that could improve traffic throughput would be welcome and so Queenstown RNP entered Stage III of its evolution.

Stage Three RNP.

What was required to improve efficiency was to find a means by which arrivals and departures could be kept apart in the absence of a radar environment. This was achieved by redesigning the RNP procedures to provide routing that separated the lateral profiles and altitude requirements that kept aircraft apart. The original RNP procedures called for a design that almost exactly over-laid the flight paths of the VOR/DME approach to prevent the complication of controllers dealing with inbound traffic from different sectors of their airspace. Now RNP at Queenstown has evolved to the stage where it is fully integrated and utilised by a range of airlines, to the extent the previous routing limitations are no longer relevant.

For GE (Naverus), this was a case of going back to the drawing board to redesign the procedures. They worked closely with Airways NZ to provide design changes that complied with air traffic controller feedback and input from airspace stakeholders. Major jet operators such as Qantas, Jetstar, Virgin and Air New Zealand also worked in co-operation, while NZ CAA bore the final responsibility as the regulator to sign off on the Stage III procedures.

In a major exercise in collegiate co-operation, the various groups worked together over 18 months to achieve a series of arrivals and departures that complied on all grounds of safety and efficiency. Having been trialled in flight simulators, the new provisional procedures were flown by a Qantas 737-800 in visual conditions to see how the new routing fared in the real world. The results were sound.
During the design process there were challenges that included the re-design of airspace over Lake Wakatipu, but ultimately the end result was the unveiling of the new Stage Three RNP procedures on November 15. Queenstown and RNP were now ready to take the next step.

The Next Step.

The new Stage III RNP procedures offer improved efficiency on a number of fronts. The separation offered by the new designs immediately offers a doubling of arrivals in instrument conditions from six to twelve arrivals per hour. That equates to 1,000 income-generating tourists per hour and is welcome news to Queenstown and its businesses. Similarly, for a Boeing 737 the payload uplift from the more limiting Runway 05 is increased by 1,400kg. Now, seats that once had to be left empty to meet ‘engine-out’ climb performance requirements can be filled.

Just as the original RNP procedures reaped operational benefits over the traditional VOR/DME non-precision approach, the new Stage III procedures offer gains over its own RNP predecessors. And while the retirement of the procedures that forged the way for RNP can be seen sentimentally as the passing of a generation, it is testament to the flexibility of RNP technology that it can be enhanced to provide even greater efficiencies. Similarly, the implementation of Stage III demonstrates the maturity of the major airlines to work alongside each other with GE and the NZ CAA to achieve the safest and most efficient outcomes.

For the crews, the new procedures called for ground school briefings and flight simulator training before they fly the real procedures in earnest. The training delivered engine failures and system anomalies that called for the flight crew to not only fly the procedures, but conduct missed approaches and extract the aeroplane safely in the event of an emergency. Simulators also offer the luxury of ‘freezing’ the aircraft in flight and reviewing the approaches to enhance situational awareness; something that cannot be achieved in the actual aircraft.

Aviation is a dynamic environment that continually seeks out the best means to achieve its goals. RNP is no exception and just as the first operations into Queenstown caught the attention of the aviation world, its latest offerings are set to be watched with interest as well. However, far from being the end of the story, the RNP Stage III procedures merely open a new chapter in this growing means of guiding air traffic. For Queenstown, it is not so much ‘farewell’ to the Stage I procedures that forged the frontier, but ‘welcome’ to the next step.