Two altimeters
Thread Starter
Joined: Nov 2000
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From: Cambridge, England, EU
Two altimeters
There's posh - I'm used to only having one.
So, what do I do with them? Clearly there are many possible choices of combinations (a) as to what to set the second one to and (b) which one to fly with.
For example, (1) always have QFE on the left and QNH on the right for local area/circuit, or (2) always have the one you're flying to on the left and the other of QFE/QNH on the right, or (3) always set them both the same so they're checking each other.
I gather there's no standard practice here, so one has to develop one's own habits. Which means developing one's own habits in such a way as to make it harder rather than easier to forget which is set to what, and harder rather than easier to find oneself flying off the wrong one.
(Not that it makes a lot of difference when the altitude of your airfield is measured in inches, but I do go to slightly less flat places sometimes.)
What do people do?
So, what do I do with them? Clearly there are many possible choices of combinations (a) as to what to set the second one to and (b) which one to fly with.
For example, (1) always have QFE on the left and QNH on the right for local area/circuit, or (2) always have the one you're flying to on the left and the other of QFE/QNH on the right, or (3) always set them both the same so they're checking each other.
I gather there's no standard practice here, so one has to develop one's own habits. Which means developing one's own habits in such a way as to make it harder rather than easier to forget which is set to what, and harder rather than easier to find oneself flying off the wrong one.
(Not that it makes a lot of difference when the altitude of your airfield is measured in inches, but I do go to slightly less flat places sometimes.)
What do people do?
Joined: Jul 2002
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From: Gatwick
I do different things depending on the phase of the flight...
* Below the transition altitude and outside the circuit, both are on QNH.
* Above the transition altitude, the "primary" altimeter (usually the one to the right of the AI) is on 1013, the "secondary" on QNH.
* In the circuit, the primary is on QFE, the secondry on QNH.
As for "standard" practice - no-one ever told me anything!
Cheers,
MD
* Below the transition altitude and outside the circuit, both are on QNH.
* Above the transition altitude, the "primary" altimeter (usually the one to the right of the AI) is on 1013, the "secondary" on QNH.
* In the circuit, the primary is on QFE, the secondry on QNH.
As for "standard" practice - no-one ever told me anything!
Cheers,
MD
Press to Reset
Joined: Feb 2003
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From: Cambridge, UK
Below transition altitude for a x-country flight I'd take off with QNH on the primary and QFE on the secondary. For cruise below transition I put QNH on both, above transition 1013 on the primary and local QNH or RPS as appropriate on the other. On approach I use QFE on the primary and QNH on the secondary unless the published circuit level is given as an altitude in which case I reverse (means I always fly the level on the primary regardless of what type of level it is).
Unless of course I'm flying CB and don't want neck ache
MC.
Unless of course I'm flying CB and don't want neck ache
MC.
Joined: Aug 2000
Posts: 3,648
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From: UK
At the risk of being provocative, most people who fly around with two or more altimeters have long given up setting QFE on any of them.
I'd suggest that below the transition altitude you set a suitable QNH on both. Above that, the choice would seem to be between 1013/QNH or 1013/1013.
There are arguments both ways, but a potentially fatal altimeter error is likely to be detected faster if both altimeters are set to the same thing. Having QNH on the second gives you rapid access to your altitude, which might be useful in an emergency.
I'd suggest that below the transition altitude you set a suitable QNH on both. Above that, the choice would seem to be between 1013/QNH or 1013/1013.
There are arguments both ways, but a potentially fatal altimeter error is likely to be detected faster if both altimeters are set to the same thing. Having QNH on the second gives you rapid access to your altitude, which might be useful in an emergency.
Bug ger using QFE for a joke.
Joined: Apr 2003
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From: Midlands
I set both to QFE. The one, which is lower, I then consider the master and set QNH or 1013 on the other depending on what I am doing. If the difference is more then 75ft it is almost certain one is out of tolerance.
Rod1
Rod1
Joined: Oct 2000
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From: E Anglia
Our Arrer has two altimeters and I'd always kinda assumed that the one closest to the transponder was the one that supplied Mode Charlie with altitude information.
But now I'm not so sure........
Anyone know where transponder gets its info from? Presumably if one altimeter only in your A/c , *that* feeds the Txponder, hence the need to keep to regional QNH en route.
Safe flying
Cusco
But now I'm not so sure........
Anyone know where transponder gets its info from? Presumably if one altimeter only in your A/c , *that* feeds the Txponder, hence the need to keep to regional QNH en route.
Safe flying
Cusco
Joined: Aug 2000
Posts: 3,648
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From: UK
Anyone know where transponder gets its info from? Presumably if one altimeter only in your A/c , *that* feeds the Txponder, hence the need to keep to regional QNH en route.
In neither case does the setting on the subscale of the altimeter make the slightest difference -- the transponder always reports pressure altitude from whichever source. In the case of an encoding altimeter, the subscale setting only changes the position of the hands, not the encoder output.
Joined: May 2001
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From: 75N 16E
A recipe for disaster in my opinion. I came across QNE the other day, the altimeter reading of the airport when the subscale is set to 1013......
I learned a little trick several years ago, it entailed looking up the airport elevation BEFORE getting airborne . This allows me to land at an airfield which is not at sea level WITHOUT (yep, thats right) setting QFE.
I suppose I'm missing out on a lot of the altimeter twisting fun though. Just think, on a cross country, you first set QNH on one altimeter, and QFE on the other. You transition above the Transition altitiude and you now twist one to 1013, and set the regional QNH in the other. but hold on a minute, you now need to cross a class D zone. This may require the 1013 altimeter to be set to a local QNH, as the transition level may rise to > your FL. So you exit the zone, and reset regional QNH, but now you want to transition a MATZ. You are passed QFE, which you must now set, until you are clear and then you go back to regional QNH. Ok, you're now descending into your destination, you are passed QNH and QFE which you set. the weather is a bit crappy, you're turning base....hmmm, did I set QNH or QFE........
I learned a little trick several years ago, it entailed looking up the airport elevation BEFORE getting airborne . This allows me to land at an airfield which is not at sea level WITHOUT (yep, thats right) setting QFE.
I suppose I'm missing out on a lot of the altimeter twisting fun though. Just think, on a cross country, you first set QNH on one altimeter, and QFE on the other. You transition above the Transition altitiude and you now twist one to 1013, and set the regional QNH in the other. but hold on a minute, you now need to cross a class D zone. This may require the 1013 altimeter to be set to a local QNH, as the transition level may rise to > your FL. So you exit the zone, and reset regional QNH, but now you want to transition a MATZ. You are passed QFE, which you must now set, until you are clear and then you go back to regional QNH. Ok, you're now descending into your destination, you are passed QNH and QFE which you set. the weather is a bit crappy, you're turning base....hmmm, did I set QNH or QFE........
Joined: Jun 2001
Posts: 191
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From: London, England
I'm with englishal on this one - the less playing with altimeter settings the better - I'm sure that there are more important things to do and sooner or later you will just confuse yourself.
The more flying I do in the US the less I am convinced that QFE is necessary. Just lookup the airfield elevation and use QNH.
Below transition altitude it's QNH/QNH for me. Above it's 1013/1013. No room for confusion and it makes the cross check very easy.
The more flying I do in the US the less I am convinced that QFE is necessary. Just lookup the airfield elevation and use QNH.
Below transition altitude it's QNH/QNH for me. Above it's 1013/1013. No room for confusion and it makes the cross check very easy.
PPruNaholic!
Joined: Aug 2000
Posts: 1,615
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From: Buckinghamshire
Someone said:
Its obviously a throwback from days when a/g communications relied on the Morse code. See http://www.kloth.net/radio/qcodes.php for a very complete list!
I suppose the advantage of continuing to use such codes is that even when used verbally they provide clear and concise meaning - especially helpful in non-English mother-tongue areas of operations. For instance, in France you will often be told the "Fox-Echo" by which they mean QFE. Think also of uses such as QDM / QDR etc. - once you've learned them, its clear and less of a mouthful via r/t.
I suppose though that the heart of the question posed is whether or not it really necessary or helpful for us to use a combination of airfield and sea-level datums at all: why not just one seal -level "pressure setting" as in the US (and Australia and probably other places for that matter)? I have heard it argued that for instrument flight you are better off using QNH alone anyway - just do the mental maths for circuit and decision heights etc., avoiding the need to do similar mental gymnastics on the go-around, arguably a time when your workload will be higher.
This argument seems to make sense to me, and I find that it really isn't a hassle relying on QNH alone when in the US for example. Yet I always settle right back into using QFE when flying around here...
Would be interested to know what others think?
Andy
Why have all these Q-codes anyway?
I suppose the advantage of continuing to use such codes is that even when used verbally they provide clear and concise meaning - especially helpful in non-English mother-tongue areas of operations. For instance, in France you will often be told the "Fox-Echo" by which they mean QFE. Think also of uses such as QDM / QDR etc. - once you've learned them, its clear and less of a mouthful via r/t.
I suppose though that the heart of the question posed is whether or not it really necessary or helpful for us to use a combination of airfield and sea-level datums at all: why not just one seal -level "pressure setting" as in the US (and Australia and probably other places for that matter)? I have heard it argued that for instrument flight you are better off using QNH alone anyway - just do the mental maths for circuit and decision heights etc., avoiding the need to do similar mental gymnastics on the go-around, arguably a time when your workload will be higher.
This argument seems to make sense to me, and I find that it really isn't a hassle relying on QNH alone when in the US for example. Yet I always settle right back into using QFE when flying around here...
Would be interested to know what others think?
Andy
Joined: Feb 2003
Posts: 2,042
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From: Oxford
It's your right to request QNH instead of QFE, of course, but I wonder - if there's no point in QFE, why are the military so keen on it? I know they*'re a bunch of traditionalists, but surely there must be some point?
Tim
*(OK, technically 'we'...)
Tim
*(OK, technically 'we'...)
Cut & Paste Intellectual
Joined: Jul 2003
Aviation Qualifications: PPL
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From: Durham
Two altimeters - There's posh - I'm used to only having one.
Handy safety tip on precision or non precision approach is to have both alts set to same reference datum ( preferably QNH ) for FAF and cross check .
Worth knowing yer tolerances - rarely do both alts totally agree ... then position error....oh dear.....
Joined: Dec 2002
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From: Bristol and Forest of Dean
Kingy's pet hate no.63
I fly an aircraft with only one altimeter that, when I'm flying solo, can't be reset in flight (it's in the front, I'm in the back!). with no radio I set it to my known strip elevation to give 'my' QNH.
Just add the field elevation on to your curcuit height at your destination (it's on the map for crisesakes!) and bobs your uncle.
I must admit it can get a little 'fun' adding or subtracting the 30fts on the rare occasions when I have to use the radio to alight at a larger field though....
But generally excessive altimeter twiddling is needless for uncontrolled VFR flight in the UK. In fact, I feel there is a safety issue with everyone flying on the same regional.
You can have your thread back now gents!
Kingy
I fly an aircraft with only one altimeter that, when I'm flying solo, can't be reset in flight (it's in the front, I'm in the back!). with no radio I set it to my known strip elevation to give 'my' QNH.
Just add the field elevation on to your curcuit height at your destination (it's on the map for crisesakes!) and bobs your uncle.
I must admit it can get a little 'fun' adding or subtracting the 30fts on the rare occasions when I have to use the radio to alight at a larger field though....
But generally excessive altimeter twiddling is needless for uncontrolled VFR flight in the UK. In fact, I feel there is a safety issue with everyone flying on the same regional.
You can have your thread back now gents!
Kingy