EGSS Rwy 04 Displaced Threshold

[MrHorgy]

This has been bugging me for the 4 years i've been at Stansted, maybe one of you boffins knows...

Why is the threshold for Rwy 04 at Stansted displaced? There is no terrain considerations, the A120 doesn't seem to have obstructions impeding the ILS surface, and there is plenty of room for CAT III lighting (so it would seem) without a displacement. I am stumped!

Horgy

[First.officer]

MrHorgy,

Believe the reason for the displaced threshold on RW04 was effected as part of the Stansted Gen. 2 development proposals.....the reasoning as part of this was that after analysing the fleet mix using the airport, it would allow the noise contour of aircraft using the aerodrome to be moved closer to the aerodrome boundary. I have seen some charts out there with the various decibel restrictions and associated wind corrections etc., can try and find them if it's of interest, but think that is why you have a 300m displacement.

F/o

[General_Kirby]

It was displaced around te same time as the 'new' high speed exit was built on 04. What is now QR. Prior to this on easterly ops runway capacity was affected by the distance of the high speed exit from the touchdown zone. Medium traffic generally took a lot longer to vacate than they did on westerly ops. To the point where it was common to have an extra mile between landers to get a departure away.

However BAA displaced it and built a new rapid exit further on from the current one. Then pilots of a certain Irish carrier would always plan for the second exit(closer to their stands) and thus the whole thing was a bit of a waste of time as the distances were the same. (300m displaced threshold- new exit 300m further on...)
Displacing threshold also led to some very restrictive rules on the northside of the airfield to protect the glidepath.

[MrHorgy]

Interesting. Seems like a colossal waste of time then looking at the way the new RET is designed.

You mention medium traffic took longer to vacate - is this because they could not make the first RET and therefore rolled to the end to vacate? Google Earth has actually imagery of them building the taxiway and before the threshold was displaced and would seem to show adequate distance to make the exit? Maybe i'm not looking at it right...

Regarding noise - as a former resident of B Stortford, you might be onto something, however I always found the noise was a problem when 04 was in use for Departures, and the wind came from JUST the right direction. Many a few curses word were hurled in the direction of FedEx and GSS when hungover and still in bed!

Horgy

[General_Kirby]

No I don't mean they had to roll to the end. Landing on 22 most M aircraft could carry a lot of energy into NR to vacate, or a well planned roll down to LR. On 04 most M aircraft had simply ran out of speed and 'expediate right' was well used as they trundled towards the exit. This was for the majority of landings...of course a good pilot with well planned brake settings etc could still wizz of 04, but the average runway occupancy times were way higher than 22.
Displacing the threshold was supposed to shift the 'sweet spot' of perfect speed to vacate rapidly closer to an exit. But as I say on 22 there was an incentive to make first high speed to save taxy time. On 04 the incentive for most ryanairs was the 2nd exit to be closer to C and D whereas easy would try and use the first.
A standard pack gap on 04 was 4 miles, after the new exit and displaced threshold 3miles was much more frequently used, the standard for 22 thus increasingly capacity on easterlies.
hadn't been aware of the noise reasons but they make sense as well.

[Reflex]

I think you'll find that there wasn't enough room for all the required App lighting.
The min RVR for 04 was reduced to the usual 550m for CAT1 when the runway threshold was displaced, before that it was around 700m (I think)

[Musket90]

From a boffin - Main reasons for the displaced threshold.

1. Before QR was built the capacity on 04 arrivals was less than 22 because the longer distance from the original threshold to PR and it's 30 deg angle design increased runway occupancy time. Also the touchdown zone using the original 04 threshold was uphill which had the added effect of slowing aircraft quicker and taking longer to get to PR to vacate the runway. Now that 04 is displaced and QR has been built to a lesser 25 deg angle design this means that the touch down zone is on the crest of the hill and the exit points are a similar distance and design to those on runway 22 so arrival capacity is similar for both runway directions.

2. At the same time that QR was built for 04 arrivals the runway 22 intersection take-off point at Q was also built to assist with capacity for 22 departures and this can also serve as a 04 exit point for "heavies" or others which miss the QR exit. This meant that a 3rd runway 04 exit doesn't need to be built to maintain runway capacity when accommodating "heavies" in the long term future, so keeping costs down

Other benefits of displacing the 04 threshold:

5 x bar approach on 04
Northside movements can get get closer to the 04 Cat I holding point at G1

[MrHorgy]

Thanks for all your help guys, now I can pretend to be intelligent at work next time I fly :E

Horgy