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LHR Disruption

Old 21st Oct 2014, 12:56
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LHR Disruption

Oh there is a bit of significant weather forecast so lets just cancel a couple of hundred flights at UKS only hub airport (LHR).

I can understand this when heavy snow falls but a bit of wind-did it ever get above 35Kts did it ever have crosswind compontent greater than most modern airliners can cope with.

Why was such drastic action taken today? It must cost the airlines involved quite bit and BA a lot of grief because of all the transit pax they carry. I know LHR operates at about 100% of capacity much of the time but is a bit of wind really bad enough to impact things so badly that lots of flights have to be cancelled ina dvance -?

PB
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Old 21st Oct 2014, 13:19
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It's the joys of operating at an airfield with no stretch, and landing intervals that are tight in fine wx.
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Old 21st Oct 2014, 13:42
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It's not the crosswind component, it's the headwind component that inevitably slows down the arrival movement rate, as a moment's thought would reveal. That will always be the case unless and until time-based separation on approach (as opposed to distance-based) is adopted.
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Old 21st Oct 2014, 14:12
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Well DR, and thanks for your reply, I did give that a moments thought but I didn't think it would add up to having to cancel so many flights because of the longer final approach times. Really does show up just how desperately LHR needs a third runway even without any growth doesn't it.

Cheers
PB
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Old 22nd Oct 2014, 06:04
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As an example for the reduction in flights and the reason why. Normally it takes an aircraft around a minute to travel 3NM on final approach into Heathrow. Yesterday as straw poll in the 25kt headwind (not the strongest of the morning) I noted it took an A320 1 minute 45 seconds to fly the final 3NM.
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Old 22nd Oct 2014, 08:25
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Normally it takes an aircraft around a minute to travel 3NM on final approach into Heathrow. Yesterday as straw poll in the 25kt headwind (not the strongest of the morning) I noted it took an A320 1 minute 45 seconds to fly the final 3NM.
An average of 180 kts over the last 3 miles?!! Bit high, they are usually down to only 160 kts outside 3 miles and then slow down even further inside 3 miles. It would take significantly more than a minute to fly the last 3 miles. A 25 kt headwind component would not almost double that time.
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Old 22nd Oct 2014, 12:55
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An average of 180 kts over the last 3 miles?!! Bit high, they are usually down to only 160 kts outside 3 miles and then slow down even further inside 3 miles. It would take significantly more than a minute to fly the last 3 miles. A 25 kt headwind component would not almost double that time.
Without wanting to seem reactionary I did say "normally" and "around" a minute for the last 3NM. I wasn't being exact.

The surface wind was showing mean 25kts, with gusts higher than that. The wind would have been stronger at altitude.

I must get my watch checked then as it clearly can't have taken that long to fly the final 3 miles.
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Old 22nd Oct 2014, 13:33
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I remember coming into LHR in the late 90's and the crosswind component was so high that the spacing was of at least 3mins. The aircraft I was on was crabbing to such an extent that from my position in row 7 I could see the runway lights through the opposite side's window. The gale force winds were coming from the SW and sadly the old SW/NW runway was no more, so the last 10miles over the capital were interesting to say the least. Pilots did a fantastic job btw.



SHJ
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Old 22nd Oct 2014, 15:01
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<<so high that the spacing was of at least 3mins>>

I was a Heathrow radar controller for 31 years and I don't recall such excessive spacing for crosswind, which would equate to somewhere around 9nm. Even during single runway ops 6nm is around the norm so there must have been some other reason.
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Old 22nd Oct 2014, 19:07
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I'm sure you're right mr HD, I only knew of any spacing because the captain of the BA 767 said this over the intercom. There were massive delays due to congestion and the very strong wind was gusting dramatically and it was this (I believe) that caused the exceptional spacing. It was 1999 +- a year if that helps.


SHJ
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Old 22nd Oct 2014, 20:25
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Sorry, my old brain isn't coming up with anything! I recall extremely strong crosswinds sometime in the 70s - I think it was steady 360/50 kts or similar. We tried 05 and 10L (as it was then!) but very few aircraft made it and crews were struggling to find airfields with N-S runways for diversion. Crosswinds don't usually affect spacing in terms of what the Tower requires although they can be hell for the radar controllers. (Remember I'm talking many moons ago and things may have changed since).
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