Airfield QNH - what's the point?
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I can't see anything wrong with everyone using RPS, Terrain clearance, traffic separation, no twiddling knobs. Where would the problem be? Precision approaches in cloud/fog?
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Don't Overfill wrote:
I think he means the Scottish TMA.
Crash one, if you fly under the Edinburgh TMA on RPS there's a good chance you'll bust their airspace.
Avoid imitations
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Where would the problem be? Precision approaches in cloud/fog?
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Slightly related to this. Where we fly aerobatics our lower level is usually 3000' on the QNH, and our upper limit is FL55. In other words we are always going up and down through the transition layer.
Obviously we're not going to reset the altimeter from QNH to 1013.2 and back every time we do a loop. Instead, we simply leave the altimeter on the QNH, and use the transponder to read the FL. Any Mode-C or Mode-S transponder will display that, and the transponder output will always be relative to 1013.2.
So if you're beneath some airspace that has its lower level defined as a FL, but you are using QNH or QFE for obstacle clearance/collision avoidance, you can use the same trick. Keep track of the altimeter and the transponder, and as long as both show you to be outside CAS, you're fine.
Now my question. Does anybody have an easy-to-use map of transition altitudes in the UK? I have looked at the AIP and all it says is that the TA is 3000' in general, but 6000' in/underneath a whole (textual) list of CTRs/CTAs/TMAs. But I could not find an easy-to-use map with TAs in the AIP.
Obviously we're not going to reset the altimeter from QNH to 1013.2 and back every time we do a loop. Instead, we simply leave the altimeter on the QNH, and use the transponder to read the FL. Any Mode-C or Mode-S transponder will display that, and the transponder output will always be relative to 1013.2.
So if you're beneath some airspace that has its lower level defined as a FL, but you are using QNH or QFE for obstacle clearance/collision avoidance, you can use the same trick. Keep track of the altimeter and the transponder, and as long as both show you to be outside CAS, you're fine.
Now my question. Does anybody have an easy-to-use map of transition altitudes in the UK? I have looked at the AIP and all it says is that the TA is 3000' in general, but 6000' in/underneath a whole (textual) list of CTRs/CTAs/TMAs. But I could not find an easy-to-use map with TAs in the AIP.
I fly from Redhill, the threshold elevations are 149 feet. We fly circuits 1000 ft (ish) AAL at 1200 ft Redhill QNH. We have a 1500 ft "shelf" beneath the Gatwick Zone to fly under so use 1400 ft QNH.
If I move to Farnborough after departure, I cannot remember their QNH ever being more than 1 Mb different to Redhill.
It all seems pretty simple and straightforward to me .... any action you relate to feet above aerodrome, just add 200 ft, (that's if you really need an altimeter to tell you when to retact take-off flap on the climb or cancel carb heat on finals.)
When I fly in the USA (KFLY elevation 6874) the knob doesn't screw far enough to use QFE. Indeed it isn't even refered to anything other than "altimeter".
If I move to Farnborough after departure, I cannot remember their QNH ever being more than 1 Mb different to Redhill.
It all seems pretty simple and straightforward to me .... any action you relate to feet above aerodrome, just add 200 ft, (that's if you really need an altimeter to tell you when to retact take-off flap on the climb or cancel carb heat on finals.)
When I fly in the USA (KFLY elevation 6874) the knob doesn't screw far enough to use QFE. Indeed it isn't even refered to anything other than "altimeter".
Last edited by Dave Gittins; 12th Jul 2012 at 13:02.
Apart from airfelds situated under TMAs, the RAF tend not to use 'real' QNH. Many years ago, they tried changing to it; all MOD airfields had their procedures redesigned as QNH approaches; all MOD airfields had a presentation on the new procedures, and they were brought in. Then with little fanfare, they were changed back to QFE procedures!
Rumour had it that a senior RAF officer had not heard of QNH procedures and had set the pressure setting given to him thinking it was QFE, thereby nearly having a 'nasty', and he was senior enough to rule that QNH procedures were 'dangerous' and require a return to QFE procedures.
How true this is I don't know, but the result was the RAF initially at least, started using just QFE, SPS and RPS. Departure would be on QFE, changing to SPS at transition altitude (yes they did use that) or if remaining low level, changing to RPS outside the MATZ.
Rumour had it that a senior RAF officer had not heard of QNH procedures and had set the pressure setting given to him thinking it was QFE, thereby nearly having a 'nasty', and he was senior enough to rule that QNH procedures were 'dangerous' and require a return to QFE procedures.
How true this is I don't know, but the result was the RAF initially at least, started using just QFE, SPS and RPS. Departure would be on QFE, changing to SPS at transition altitude (yes they did use that) or if remaining low level, changing to RPS outside the MATZ.
Last edited by chevvron; 12th Jul 2012 at 14:14.
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Crash one, if you fly under the Edinburgh TMA on RPS there's a good chance you'll bust their airspace.
D.O.
D.O.
Anyway, apart from using QFE or airfield QNH for a precision approach, if everyone in the region was on RPS?
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Credit the RAF with a little intelligence !
I can assure those who think that the RAF had never been told about QNH approaches that is not the case, in fact they a few years back changed to QNH approaches, however this did not best meet the operational requirements of recovering fast jets in bad weather usually using PAR.
So the RAF switched back to QFE, if you operate into an RAF airfield in an aircraft that can't use QFE they are quite able to adapt the system to enable you to fly the approach using QNH.
So the RAF switched back to QFE, if you operate into an RAF airfield in an aircraft that can't use QFE they are quite able to adapt the system to enable you to fly the approach using QNH.
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The QFE/QNH debate has been around as long as aviation has existed!
To me QNH is more logical - have the altimeter set to something you can relate it too, such as elevations of topo features (yes I know IAPs show height AAL too but am thinking more topo charts and even grid MORA on instrument area charts).
If you've been brought up on QFE and never done anything different the idea of flying on QNH seems quite alien - I was chief trainer for a Company when we changed from QFE to QNH operation - we put everyone in the simulator for a couple of hours and the switch was a non event. Having spent many an hour in the back of the sim I can tell you that there are far more altitude busts using QFE than there are with QNH.
As for the RPS - it's a throw back to the days of non radio aircraft and you needed a safe altimeter setting to fly (say) from London to Prestwick so the MET office would give you the lowest forecast QNH for the route - later on they introduces Altimeter Setting Regions (eg Barnsley)to enhance the process.
If I had anything to do with it I'd bin RPS completely (I await the flames now LOL) and also QFE - let's have aerodrome QNH as standard.
As a footnote in the USA they don 't call it QNH - it's the "Altimeter Setting" - speaks volumes.
To me QNH is more logical - have the altimeter set to something you can relate it too, such as elevations of topo features (yes I know IAPs show height AAL too but am thinking more topo charts and even grid MORA on instrument area charts).
If you've been brought up on QFE and never done anything different the idea of flying on QNH seems quite alien - I was chief trainer for a Company when we changed from QFE to QNH operation - we put everyone in the simulator for a couple of hours and the switch was a non event. Having spent many an hour in the back of the sim I can tell you that there are far more altitude busts using QFE than there are with QNH.
As for the RPS - it's a throw back to the days of non radio aircraft and you needed a safe altimeter setting to fly (say) from London to Prestwick so the MET office would give you the lowest forecast QNH for the route - later on they introduces Altimeter Setting Regions (eg Barnsley)to enhance the process.
If I had anything to do with it I'd bin RPS completely (I await the flames now LOL) and also QFE - let's have aerodrome QNH as standard.
As a footnote in the USA they don 't call it QNH - it's the "Altimeter Setting" - speaks volumes.
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easy-to-use map of transition altitudes in the UK?
The Americans have mastered the art of practicality in most aspects of life. Aviation is one good example.
Europe ( in particular the UK ) seems to take pleasure in the fact that they are stuck in the theoretical world.
Witness the typical response to a student in a flight school in the UK, who trained outside Europe (how dare they!) and asks about QFE, or to explain the transition level system here.
QFE should go in my opinion. If someone can't add field elevation onto the circuit height then, well....
Of course QNH & QFE should go, along with the rest of the Q-Codes, RPS, signal squares, overhead joins and all the other archaic anachronisms that were introduced when Morse Code was the height of sophistication! When the pilot of an HP42 was trying to find Croydon in the 1930s they were relevant, unfortunately the UK has clung onto them ever since!
Last edited by Thud105; 13th Jul 2012 at 09:07.
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Well it makes it all sooo interesting when flying below transition level outside CAS. Other traffic might have RPS, QNH, QFE, set, and they might be talking to London info, or a local A/F , or even 'safetycom'. I like to fly at altitude plus 500 feet (as in France) to minimise the chances of an intimate encounter
QFE should go in my opinion. If someone can't add field elevation onto the circuit height then, well....
Flybymike - Precisely. I like to join the circuit at (say) 1000 feet above the field, and not one thousand three hundred and forty nine feet nine and three quarter inches above sea level...
But when they are the same altitude what's wrong with joining the ccircuit at 1350 QNH and then you know exactly how high you are above all the things on your chart ??
But when they are the same altitude what's wrong with joining the ccircuit at 1350 QNH and then you know exactly how high you are above all the things on your chart ??
A VFR pilot's workload is highest during approach and landing. You want to throw in some mental maths for no good reason that I can see.
We don't have any field elevations high enough to justify a QNH approach.
Some airfields, such as Redhill, use QNH due to being in a CTR. The vast majority don't.
We don't have any field elevations high enough to justify a QNH approach.
Some airfields, such as Redhill, use QNH due to being in a CTR. The vast majority don't.
Last edited by Flyingmac; 13th Jul 2012 at 12:56.