RWY 35 in Canberra

[Maikha Ly]

G'day all

Something that's always had my curiousity since I went to the Canberra Airport Open Day last year, is the displaced threshold of Runway 35, the longer of the two runways at Canberra. Here's a Google Maps location just to illustrate.

http://maps.google.com.au/maps?q=Can...18359&t=h&z=17

Does anyone know the reasons for this displaced threshold? Are/were there obstructions to the South of the Airport that required it to be moved forward to meet landing profiles, or does it have to do with the close proximity of the road (Pialiggo/Fairbairn Ave) right behind it?


Any insight into this would be much appreciated, thanks!

[Jason H]

They displace the threshold so as to achieve obstacle clearance on an approach. The terrain that is requiring the displaced threshold could be as far as 10nm out, which is probably the case in Canberra with the mountains to the south.

[Maikha Ly]

Thanks for that, Jason H!

[Jakef]

I wonder how displaced thresholds work on GA only runways, because where I do my flying out of there is quite a sizable one on a small 800ft GA runway. Sizable in the sense that it is possible in the aircraft I fly to actually takeoff before the piano keys
There is a road near the end of it and a large mountain quite a distance away but they aren't really obstacles for the aircraft that use it.... hmm

[Jason H]

Jake, are you referring to Camden by any chance?

Although the majority of GA operations are by light aircraft in visual conditions, there are also aircraft who need the displaced threshold for instrument approaches. At Camden, the displaced threshold is really the most important at night when visual circling. Because you can't see the terrain and obstacles, you have to descend at normal rates of descents from a position of downwind (most likely). If you aimed for the start of the runway rather than the threshold, you can see that the minimum obstacle clearance will be breached as you descend on final.

The runway before the threshold is not designed to bear the weight of an aircraft landing on them, so they also are built to increase the take off distance, rather than the landing distance, as most aircraft would require a longer take off distance than landing distance.

JFK is an interesting example, as one of their runways, which is already a bit over 4km long, has a displaced threshold of around 1km. As there is not significant terrain on that runway's approach, I have heard that it is displaced for noise abatement purposes.

[Jakef]

No not camden. Not sure about the night thing because it isn't equipped with lighting and is day use only. There is a fence pretty close to the end of the runway so maybe that classifies as an obstacle for it.

[Hugh Jarse]

Jake, a displaced threshold is usually placed due to obstacles in the approach path (as a previous poster wrote). In Camden's instance, it's due to the hills, etc immediately northeast between Macquarie Grove and Cobbity Rds, along the flight path.

[A McLaughlin]

With CBR, there are no real obstacles, but I wonder if the airport owner is trying to keep the aircraft as high as possible over the planned suburb of Tralee (10km to the south!) as there have been some noise concerns.

There is also a road running round the immediate end of RWY35 so that might be a consideration too?

[Hugh Jarse]

I don't think Airservices consider "planned" suburbs, A. Mc. Almost all approaches that I know of are a standard 3 deg path. Plus, I don't think the developers of Tralee won any noise concessions against Mr. Snow.

The landing threshold of 35 in CB is in the same place it's been for the last 20 years. So I would again suggest it's obstacle-based. :-)

[Grahame Hutchison]

I think that the Canberra RDS provides the answer - OBSTACLE