"Phil Layton" wrote in message
...
We were doing quite well this morning with a steady flow rate matching the
actual landing rate. However this afternoon we had to change runways twice
as the front just nudged enough E to bring us 'Westerlies' for an hour.
This can be seen from the METARs:
EGLL 081750Z 12009KT 9999 FEW033 BKN044 07/06 Q0967
EGLL 081720Z 11006KT 080V150 9999 BKN042 08/06 Q0966
EGLL 081650Z 12006KT 090V230 9999 FEW034 BKN042 09/06 Q0966
EGLL 081620Z 22006KT 190V280 9999 FEW021 SCT034 09/05 Q0966
EGLL 081550Z 21007KT 9999 FEW034 SCT041 09/05 Q0966
EGLL 081520Z 15008KT 9999 FEW026 SCT036 09/06 Q0965
EGLL 081450Z 15009KT 9999 FEW009 SCT018 BKN030 08/06 Q0965
EGLL 081420Z 13012KT 9999 FEW010 SCT017 BKN025 08/06 Q0965
EGLL 081350Z 13012KT 9999 FEW009 BKN015 07/05 Q0965 TEMPO BKN012
Holding delays went up as a result.

Not predicted on the TAF, Jon, but I guess it might have deserved a Prob10
in the days we used to have them!

Phil

Certainly an interesting day weatherwise.

Saw a Facebook update from one of our recently-gratuated trainee air traffic
controllers that simply said "966!!" We dont get that low in the sims!

Extra care needed in the LTMA to watch out for level busts I expect.

Jim, Bournemouth
--
Bournemouth Weather readings online: http://www.g0ofe.com/weather

On 08/11/2010 21:52, Jim Smith wrote:


Certainly an interesting day weatherwise.

Saw a Facebook update from one of our recently-gratuated trainee air
traffic controllers that simply said "966!!" We dont get that low in the
sims!

Extra care needed in the LTMA to watch out for level busts I expect.

Jim, Bournemouth

I did write to folks in ATC on Saturday morning saying that the QNH
would go below 976 on Monday morning ( I said 09Z but in fact it was
06Z!!) and said that it would go to 968 - and it went to 965mb..so not
too bad.

The issue is MSL (Minimum Stack Level) goes up to FL90 below 976mbs to
provide 1000ft separation from 6000ft QNH - which has capacity impacts
in the LTMA.

Phil

Phil Layton wrote in news:8jrb1cF3e5U1
@mid.individual.net:

The issue is MSL (Minimum Stack Level) goes up to FL90 below 976mbs to
provide 1000ft separation from 6000ft QNH - which has capacity impacts
in the LTMA.

Translation for a numpty here please Phil !

Richard

On 08/11/2010 23:01, Richard Dixon wrote:
Phil wrote in news:8jrb1cF3e5U1
@mid.individual.net:

The issue is MSL (Minimum Stack Level) goes up to FL90 below 976mbs to
provide 1000ft separation from 6000ft QNH - which has capacity impacts
in the LTMA.

Translation for a numpty here please Phil !

Richard


I'll get back tonight....

On 09/11/2010 07:18, Phil Layton wrote:
On 08/11/2010 23:01, Richard Dixon wrote:
Phil wrote in news:8jrb1cF3e5U1
@mid.individual.net:

The issue is MSL (Minimum Stack Level) goes up to FL90 below 976mbs to
provide 1000ft separation from 6000ft QNH - which has capacity impacts
in the LTMA.

Translation for a numpty here please Phil !

Richard



Richard,

Aircraft that fly in the UK do so based on the airfield pressure reduced
to MSL (QNH) if they are at or below the Transition altitude which is
set at 6000ft. If they fly above the Transition altitude, they do so set
to the Standard Atmospheric Pressure (1013.2mbs). This is so that
flights on long haul do not have to set different pressures over various
parts of the world.

The SIDs from Heathrow (Standard Instrument Departures) generally all
climb to 6000ft (QNH). The arrivals come into the holding stacks at the
lowest Flight levels that provide 1000ft separation from the SIDs. So
you see we have two sets of ac flying on separate pressure settings. We
need to always provide 1,000ft separation between them. Now 6000ft on a
QNH of 1013mbs is the same as FL60 (on 1013). Therefore when pressure is
1013mbs or more FL70 is separated from 6000ft (providing the 1000ft
separation). When the pressure drops below 1013mb, we lose 32ft for
every millibar, then we have to hold at FL80. When the pressure drops to
976mbs or below, we have to hold at FL90.....all of this takes
'capacity' out of the Terminal airspace as the levels that a lot of the
aircraft fly in SE England is 'fixed' i.e they have to cross certain
points at fixed levels.

Probably not done a very good job at explaining it - the old pressure
question is a good one to get controllers getting pens and paper out...

Phil