Lowest Regional QNH?
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Lowest Regional QNH?
I haven't flashed around in a FJ for about 6 years now, but can anyone who is in current FJ flying practise tell me whether it is still standard procedure to set the lowest regional QNH for the route.
Some of you Valley types might be best to answer this.
It always dumbfounded me why we have so many regional QNHs for such a tiny set of islands - especially when you either set the lowest or the local airfield QNH. Most of my time on Tonka you'd use radalt anyway. In the US they just set the QNH of the airfield within 100miles of where they are flying - seems to work OK for them.
CPL Clott
Some of you Valley types might be best to answer this.
It always dumbfounded me why we have so many regional QNHs for such a tiny set of islands - especially when you either set the lowest or the local airfield QNH. Most of my time on Tonka you'd use radalt anyway. In the US they just set the QNH of the airfield within 100miles of where they are flying - seems to work OK for them.
CPL Clott
I don't own this space under my name. I should have leased it while I still could
Regional gives you a safe backup regardless of terrain. Rad Alt is fine if you can see 
As for setting airfield rather than regional it might be because of the small size of the island. Suppose Coningsby had one QNH and Waddington another? Which is better?
As for setting airfield rather than regional it might be because of the small size of the island. Suppose Coningsby had one QNH and Waddington another? Which is better?
In the US they just set the QNH of the airfield within 100miles of where they are flying - seems to work OK for them.
As for setting airfield rather than regional it might be because of the small size of the island. Suppose Coningsby had one QNH and Waddington another? Which is better?
So KCLT and KPTI....50 or so miles apart...both International Airports....might have a different QNH....to what effect? How much variation do you think there might be....and what effect upon altitude conflicts would it have that would matter?
Add in Altimeter Error which my foggy memory tells me is limited to +/- 70 feet....and you still should not have a problem.
Last edited by SASless; 20th Jan 2013 at 15:01.
I don't own this space under my name. I should have leased it while I still could
SASLess, oh to have a nice uniform weather system with no local pressure variations. Lucky for you old chap. As our regional are quite small and quite large variations exist it is better to have everyone on the same pressure setting.
The Regional Pressure Setting, isn't in effect a 'QNH' per se - it's a pressure datum value provided by the Met Office which has been tweaked slightly to assure that terrain avoidance will still be achieved within an entire ASR.
This whole topic is now under review as part of the ongoing Transition Altitude Harmonisation programme.
Hopefully this will result in fewer, but larger Altimeter Setting Areas.
This whole topic is now under review as part of the ongoing Transition Altitude Harmonisation programme.
Hopefully this will result in fewer, but larger Altimeter Setting Areas.
Avoid imitations
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I always thought altitude was based on sheep's legs and cow's legs.
quite large variations exist
As we do not have such a concept as Regional QNH....limit ourselves to a Standard QNH once we go to Flight Levels....we do not have a problem.
When then does the UK insist upon a different system than we do?
If safety is the issue....which system is better and to what degree?
If there is scant difference in safety....which system is easier to use?
Now I do recall having fun teasing you folks about Altimeter Settings during a Missed Approach combined with a change in the Handling Pilot... and all that....so there must be something to the fact the UK system is far more complicated than it need be. Why else would there have been that mock BA Memo on the subject?
So I repeat the question.....how big a difference can there be between two Airport QNH settings within a hundred mile radius and does it present a real hazard to safe flight?
Come on PN....educate us on the dangers of doing away with the Regional QNH system....as the USA has done by never adopting such a concept.
Are we talking FOQNH here ....... forecast QNH?
If so, these were [are?] issued centrally, every hour, for [I think I recall] the following hour. The central forecast office produced them and they appeared routinely on the teleprinter broadcast, and were added to the observation by duty Met. for ATC .......... this in addition to the actual QNH for the airfield.
I might be wrong, it was a year or 20 ago!
Right now there is a Low in the Atlantic which comfortably manages 50 mb change at surface in 10 degrees latitude, so 1 degree latitude is worth 5 mb in that area, and so 120nm would give about 10mb difference in all the measures of pressure/altitude.
That would be worth some 300 feet in the vertical between the two stations ........ not that any flier sweating on a pension would wish to fly in said conditions.
Such lows have been known to cross the UK, as every M Fish knows.
If so, these were [are?] issued centrally, every hour, for [I think I recall] the following hour. The central forecast office produced them and they appeared routinely on the teleprinter broadcast, and were added to the observation by duty Met. for ATC .......... this in addition to the actual QNH for the airfield.
I might be wrong, it was a year or 20 ago!
Right now there is a Low in the Atlantic which comfortably manages 50 mb change at surface in 10 degrees latitude, so 1 degree latitude is worth 5 mb in that area, and so 120nm would give about 10mb difference in all the measures of pressure/altitude.
That would be worth some 300 feet in the vertical between the two stations ........ not that any flier sweating on a pension would wish to fly in said conditions.
Such lows have been known to cross the UK, as every M Fish knows.
Last edited by langleybaston; 20th Jan 2013 at 15:58. Reason: addenda
SASless,
Further examples of eccentric British military altimetry procedures:
1. Transition altitudes lower than MSA.
2. QFE.
3. "Clutch" QFE - requiring an approach to be flown using the QFE of a runway at a different aerodrome.
The defenders of these practices often say something like "it works well for us, why change it?", a point that has some validity but fails to acknowledge that standardisation with the rest of the world is a valuable objective that promotes safety and aids interoperability.
That said, the same argument can be levelled at using inches Hg instead of hPa.
Further examples of eccentric British military altimetry procedures:
1. Transition altitudes lower than MSA.
2. QFE.
3. "Clutch" QFE - requiring an approach to be flown using the QFE of a runway at a different aerodrome.
The defenders of these practices often say something like "it works well for us, why change it?", a point that has some validity but fails to acknowledge that standardisation with the rest of the world is a valuable objective that promotes safety and aids interoperability.
That said, the same argument can be levelled at using inches Hg instead of hPa.
I don't own this space under my name. I should have leased it while I still could
LB thank you for putting figures to my memory. Any thoughts on the typical pressure variations over similar distances in the US?
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Thanks for the info folks. We have been debating the CAA's Transition Altitude piece and it would appear that the military wants to keep the myriad of ASRs - heaven knows why when it appears we still, and always have, set the lowest for this hour and the next!
As for UK experiencing more pressure variations than the US - ever heard of a hurricane? (and not the Hawker variety!).
Thanks again for all the input and for putting my mind at rest.
CPL Clott
As for UK experiencing more pressure variations than the US - ever heard of a hurricane? (and not the Hawker variety!).
Thanks again for all the input and for putting my mind at rest.
CPL Clott
Excluding a hurricane blundering inland, and of course setting a tornado aside as a very local crisis that only a pratt would knowingly approach, US gradients probably a bit less than the UK. I have in mind some nasty kinks in the isobars downwind of the Rockies, though!
There is also a latitude consideration in the extreme south of the States, in that large gradients just cannot build up anywhere near the Equator ......... Coriolis does not work, and, as fast as a Low is created, the surrounding air rushes in to fill it ........ like trying to dig a hole in dry sand.
Most UK forecasters never get to draw a chart much further south than 30N, and, when they have to, its a rude awakening. As for S hemisphere, I did consider standing on my head to make sense of the flows and the fronts, but even that didn't do it. My temporary job in CFO involved drawing ALL the S hemisphere at the end of a very long and no-chance-of-a-kip night shift.
YUURRRGGGGGH.
After 19 weeks I managed a dream posting out.
There is also a latitude consideration in the extreme south of the States, in that large gradients just cannot build up anywhere near the Equator ......... Coriolis does not work, and, as fast as a Low is created, the surrounding air rushes in to fill it ........ like trying to dig a hole in dry sand.
Most UK forecasters never get to draw a chart much further south than 30N, and, when they have to, its a rude awakening. As for S hemisphere, I did consider standing on my head to make sense of the flows and the fronts, but even that didn't do it. My temporary job in CFO involved drawing ALL the S hemisphere at the end of a very long and no-chance-of-a-kip night shift.
YUURRRGGGGGH.
After 19 weeks I managed a dream posting out.
Last edited by langleybaston; 20th Jan 2013 at 16:36.
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Hopefully this will result in fewer, but larger Altimeter Setting Areas.
I may be flying a dinky little C152 not a fast, shiny, noisy jet, but it still provides plenty to keep me occupied.
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and it would appear that the military wants to keep the myriad of ASRs - heaven knows why when it appears we still, and always have, set the lowest for this hour and the next!
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Originally Posted by DX Wombat
If you are brave enough to speak to a certain Midlands airport ATC you may, if they bother to let you know, get another one to work with.
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