Runway change

drdeadlift

Taking Heathrow as an example,lets say the winds change direction at which point will the approach controller change arrival traffic.
Is there a distance out at which aircraft can change from one star to the other.
As well as in the air traffic,what happens if there is a Que of aircraft (maybe 7+) lining up on lets say on either 27L or right.The winds change and they are looking at a tailwind take off at which point will the traffic about turn.
Im sure this doesnt happen too often but from time to time im sure it must,doest the crap hit the fan if the winds change direction 180 deg with winds above 15kts?

basill

Most commercial aircraft have a limit of 10kts tailwind. A lot of airfields will state in the AIP (or in our case the Jeppy plates) what the max allowable tailwind is before they will change a runway.

At a place like LHR they are very slick so will pick up at an early enough stage that the wind is tending from the other direction and hence plan on a change of runways. In which case traffic entering the TMA will enter the various holds whilst the remaining traffic is landed/departed.

For traffic at the hold waiting for departure then it really depends on a host of factors. First is performance for the aircraft. A very heavy category a/c might not be able to take a 10kt tailwind. Temperature and pressure will also impact. Also the captain may decide that s/he is not happy with the tailwind and request a backtrack for the reciprocal.

At the end of the day its ATC and the airport operators trainset so we could encounter a significant delay regardless.

Tenger

drdeadlift wrote: »

.....
Im sure this doesnt happen too often but from time to time im sure it must,doest the crap hit the fan if the winds change direction 180 deg with winds above 15kts?

Looking at it from another PoV, I doubt that there are many occasions of a 180 degree wind change in a matter of minutes. I would assume the ATCO's are awre of an imminent wind change (weather forecast) and perhaps seperate and/or set up movement to in anticipation of this runway change.

I have been in Dublin and seen aircraft taking off from 10 while aircraft are lining up for 28 in anticipation of a runway change.
http://www.flickr.com/photos/tearbringer/4987019404/

urajoke

Plenty of occasions the wind swings quickly especially when light and and its warm the onshore versus the offshore wind. The passing of a pressure system etc etc. Believe me it happens a lot and is a pain.

1. Runway change due surface wind

2. Runway change due significant difference between wind on the approach and wind on the surface especially if surface wind is light to calm.

To answer 1. The obvious situation, but we wait till the wind gets too strong for aircraft to handle or we wait for a break in traffic to reduce the delay to traffic. Natural gaps in traffic happen periodically and we try to wait for this to happen. Sometimes we get no gap in traffic and that's when it gets messy, So messy we are cleaning it up for hours afterwards.

Met Eireann have had lots of retirements recently and a lot of experience has left with them. Weather reports have got poorer as a result. Sometimes an unpredicted wind happens which puts the cat amongst the pigeons. We call the forecaster and the general response is "we don't know how long it will last" so we have a decision to make, stick with the runway or make the change causing delays. So we change and then we might have to change again 20 mins later because the wind swings back.

Sometimes they are planned hours in advance as the TAF reports a wind change at 1600z and low and behold the wind swings on time as planned happens 5-10% of the time max.

2. The second is a tower request due to PIREP's(pilot reports) and observed GS(ground speed) over the last few miles of the approach followed by traffic rolling passed the RET's(rapid exit taxiways) making it harder for the tower to release traffic in the given standard 6nm gap. Usual GS is 130-150kts from 4nm for a A320-B737 but with a tailwind on the approach this may rise to 220kts 12-->7nm then 180kts till 2-3nm and then standardish speeds as the wind starts to swing to a light headwind.

Heathrow NEEDS to plan their runway changes well in advance as they have huge volumes of traffic to shift but they do suffer from late or little notice runway changes which are devastating in terms of delays.

xflyer

Met Eireann have had lots of retirements recently and a lot of experience has left with them. Weather reports have got poorer as a result.

Aha, that's the explanation then. I noticed a definite decline in the general standard of forecasts of late. Then there's the contradictions between the TV weather forecast, the website versions and the TAFs.

LOccitane

xflyer wrote: »

Aha, that's the explanation then. I noticed a definite decline in the general standard of forecasts of late. Then there's the contradictions between the TV weather forecast, the website versions and the TAFs.

Indeed.

The less experienced staff at Met Eireann also like to stick rigidly to NWP Guidance - with a focus on only a small collection of the wide array of Guidance on offer also. This often leads to them putting out real time forecasts suggesting 'X' when the current conditions at DUB for example are actually indicating otherwise.

xflyer

Had that experience more than once. A recent very gloomy TAF in my hand and looking at the lovely blue sky overhead.