Let’s look at flying a jet into Queenstown.
Our guest writer for today is Captain Dave Griffin, Air New Zealand. Although he has recently moved to the B777, he spent a few years on the A320 and here, he writes about flying into Queenstown using the very clever RNP approach.
Captain Dave Griffin
In the early days of jet operations into Queenstown, in the 737-200, we had to fly the last 20-30 nautical miles visually. We would fly either directly into the airport by descending steeply once past the Cardona ski area; or if the cloud or visibility didn’t permit that, we would fly an NDB (old Nav aid) approach at Alexandra and then follow the Clutha and Kawarau Rivers to Queenstown airport. This was really good fun flying and pretty unusual in a Jet aircraft.
(Melissa here – as a Flight Attendant down the back, the route - visually following the river- was astounding, both for astonishing views but also because as we flew up the Gibbston Valley, the mountain tops were above us on both sides! We had to have faith in the flying skills of our pilots as we sped past the very close mountain sides – and of course, we did have faith in them!)
The route from Alexandra to Queenstown would typically be flown at about 1500’ above the ground level, at 150 knots with about half flap and the gear down. To this day, only Captains get to fly into Queenstown.
The Alexandra NDB to Queenstown visual procedure had two mapped locations where the aircraft could safely be turned around and flown back out of the tight valleys if the weather was not good enough to continue.
From the mid-1990s, this procedure was no longer required when a VOR Nav aid was installed on Slope Hill near the Queenstown Airport. This new approach got us down to about 3000 feet above the airfield. Quite a high minimum altitude compared to VOR approaches at other NZ Airports like Auckland and Christchurch which have minimums of about 500’.
When designing instrument approaches many factors are taken into account, such as
· the accuracy of the ground Nav aid,
· distance from the Nav aid,
· on board equipment capability,
· the missed approach single engine climb ability of the aircraft and
· maximum expected winds,
These are the reasons for the much higher minimum altitude on the Queenstown VOR approaches.
The advent of GPS, modern on-board navigation computers and accurate auto pilot systems led to the design in the mid 2000’s of the Required Navigation Performance (RNP) set of principles and rules.
These describe the requirements for:-
· onboard system,
· number of GPS receivers,
· satellites visible,
· on-board checking for errors,
· whether a flight director or Auto pilot is in command
and then relate this to clearance from terrain.
With no ground based Nav Aid errors to consider (which get bigger with distance from the aid) the margin of error is the same for the whole approach. This permits terrain as close as .2 nautical miles (about 370m) either side of the aircraft.
Back to Queenstown.
A straight-in approach, as found at most other airports would soon find mountains in the way at Queenstown - so a curving approach is needed. See the approach chart for Runway 23 below.
RNP approach for Runway 23
The designer of this approach was able to keep the descent slope at 3.2 degrees – only slightly steeper than the average 3 degree slope found on most instrument approaches - and well within the ability of modern aircraft to fly at a stable speed.
The approach winds like a snake through various valleys and saddles starting a 10000’ over the Pisa Range on down to just 400’ above the runway. The same RNP rules apply to the missed approach. With an engine failure at the lowest height of the approach, the aircraft could follow the missed approach track safely away from terrain and climb to a safe height on the way through a valley to Invercargill.
How to fly this approach?
Let’s assume we are flying in from Christchurch in an A320. The standard arrival gets the aircraft to the first point on the approach, ATKIL, at a max speed of 210 knots and at 10,000’.
It’s important to be at or below to this speed – it’s a design parameter and combined with maximum wind and the navigation capability of the aircraft will keep it flying the track accurately.
Being at or close above 10000’ is also important as from ATKIL on there is not much distance to lose height as the approach proceeds.
Between QN780 and TOGOX, slow to 170 knots and get Flap 2 out. In the Airbus this combination of Flap 2 and 170 knots is an ideal approach configuration, there is enough drag to keep a little thrust on, and if an updraft or tailwinds make staying on the vertical path challenging, speed brakes and putting the gear down early will usually create enough drag to keep on the path.
Passing ATVUP can be the most turbulent point of the approach as strong westerly winds above mix with winds following valleys below. I have encountered some of the most brutal turbulence experienced anywhere in that area. It amazed me how accurately the autopilot managed to follow the profile through this.
Approaching LARAV the gear is lowered and landing flap set, the aircraft then flies the last 2000’ on towards the runway in a stable approach configuration of Vref plus 5-10 knots – about 140 to 150knots.
Depending on the weather I would typically disconnect the autopilot at about 800’ above the airport and line up with the runway for landing.
It’s in the last 1000’ or so that the fickle winds of the Queenstown basin often lead to the approach becoming ‘unstable’ and needing to go around and try again. Winds from the south often pass through the gap just south of the airport and then swirl around to be a tailwind in the space from about 1000’ down to 500’ or so. In response the auto throttles will reduce thrust, sometimes to idle and often the airspeed will increase above our limit of +10knots – which is the trigger to go around and either enter the figure 8 shaped circuit or fly the full missed approach up to 10000’ to try again or divert.
The runway is pretty short and the overrun unforgiving, so the touchdown point is critical, landing on the white touch down markers painted on the runway between the PAPI’s. If not, just a hundred metres later and it’s time to go around and try again.
The advent of RNP has certainly increased the reliability of flights into Queenstown. It’s rare to not be able to land due to the cloud base or visibility, but the cross wind and tailwind still causes a number of diversions.
Thanks Dave.
For those who have not had the fortune to fly into Queenstown recently, here are some YouTube videos which demonstrate the RNP approach into Queenstown.
https://www.youtube.com/watch?v=Yeo2gUoTO4Q&ab_channel=AviationWeek - a educational video made by Queenstown airport explaining how the RNP and night landing operate at the airport
https://www.youtube.com/watch?v=biCA3qbDD5w&ab_channel=NZAviation - a jump seat view of an ATR landing coming through the Kawarau into Queenstown
https://www.youtube.com/watch?v=7mxmFCw-Dig&ab_channel=MrGoodViewsPilot - an amazing video of an RNP approach from the right hand seat, set to music - most inspirational
