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QNH vs. QNE

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Combrinck created the topic: QNH vs. QNE

When I call the Kingaroy AWIS (Elev 1492), it says “QNH” and then the reading.

From BT Vol 2, page 251, should this not rather be “QFE” since the AWIS is giving the local aerodrome pressure at Field Elevation?

Further, if I therefore fly into Kingaroy and know a pilot in a plane on the ground at that time, I can ask them to adjust their Altimeter to “0” Ft which will give them the QFE reading on the subscale to pass on to me, which I will then enter into my plane’s subscale to give me an accurate height reading above the ground at Kingaroy. Is that correct?

Thanks.
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  • John.Heddles
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John.Heddles replied the topic: QNH vs. QNE

should this not rather be “QFE” since the AWIS is giving the local aerodrome pressure at Field Elevation?

One might have to ask whence you obtained that idea ?

If I look up the AIP, I find 109 references to QNH. On the other hand, I find 0 (zero, zip, nada, ziltch) references to QFE. We don't use QFE in Australian practice although some folks may do so for specific purposes - ad hoc procedures can, and sometimes do, lead folks into all sorts of bad things, so perhaps not really a good idea. There is not much need for QFE - flying on QNH doesn't create any difficulties once you gain a little bit of experience.

So, where does it come from ? Historically, QFE has been used overseas for whatever reasons but not here. Added to this is the potential for legal argument after the event due to your not following AIP procedures ?

since the AWIS is giving the local aerodrome pressure at Field Elevation?

'Fraid not. You might have a quick look at AIP Gen 3.5.7.4.3.d.

Further, if I therefore fly into Kingaroy and know a pilot in a plane on the ground at that time, I can ask them to adjust their Altimeter to “0” Ft which will give them the QFE reading on the subscale to pass on to me, which I will then enter into my plane’s subscale to give me an accurate height reading above the ground at Kingaroy. Is that correct?

But why would you bother ? You have just created a nightmare for pilot separation interactions (unless everyone were to be on QFE).

[Just as a very minor aside, I presume you intended your thread title to refer to QFE rather than QNE ?]

Engineering specialist in aircraft performance and weight control.
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Combrinck replied the topic: QNH vs. QNE

(Yes, I meant to say QFE and not QNE - sorry)

I simply read Bob Tait RPL/PPL Sudy Guide Volume 2, page 251, which says: "To allow the altimeter to indicate height above the aerodrome, the atmospheric pressure at the field elevation must be set. This is called QFE and for an aircraft in flight, it would have to be passed by an observer on the ground. For an aircraft at the aerodrome, QFE can be found by adjusting the altimeter knob to make teh main scale read zero. The value which now appears in the subscale window is the atmospheric pressure at the field."

Did my initial explanation differ from the one above? It may have, but I cannot see if it does. While the AIP does not reference QFE it is not evident from the Study Guide that this practice is not used in Australia. On the contrary.

" ... There is not much need for QFE - flying on QNH doesn't create any difficulties once you gain a little bit of experience."

Forgive me but I'm not yet clear on this issue:
Today I phoned the AWIS at Kingroy (Elev 1492) and it gave me QNH of 1014. Then I phoned the Sunshine Coast AWIS (Elev ~ sea level). and it gave me a QNH of 1012. These airports are around 100NM from each other. So, theoretically, I will have used a QNH of 1012 if Kingaroy did not have an AWIS.

Alternatively, I may have asked a friend sitting in a plane on the ground at Kingaroy to give me the QFE by setting the mainscale on his altimeter to 1492 and reading the 'QNH' (QFE) from it, which I would then use to dial into my Altimeter as I approach Kingaroy.

So, by using QFE I would have had an accurate reading in my approach to Kingaroy aerodrome. By using the QNH at Sunshine Coast, however, (1012) my Altimeter reading at an airfield with an elevation of ~1500 Ft would have shown a vastly different reading.

Or, am I missing something? Sorry, don't mean to be pedantic but this is a practical matter which I do not yet fully grasp.
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Combrinck replied the topic: QNH vs. QNE

I think I see my issue here, ... I am bringing Pressure Hight into the equation, which I should not do.

In the end, the difference between 1012 and 1014 is not a lot. So, even if I had used the QNH for the Sunshine Coast airport it would not have made too much of a difference (say around 60 Ft or so).

Is that correct?
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John.Heddles replied the topic: QNH vs. QNE

Study Guide Volume 2, page 251, which says: "To allow the altimeter to indicate height above the aerodrome, the atmospheric pressure at the field elevation must be set. This is called QFE and for an aircraft in flight, it would have to be passed by an observer on the ground. For an aircraft at the aerodrome, QFE can be found by adjusting the altimeter knob to make the main scale read zero. The value which now appears in the subscale window is the atmospheric pressure at the field."

Did my initial explanation differ from the one above?

The question is moot as we don't routinely use QFE for Australian altimetry purposes. You appear to understand what QFE is but it really is irrelevant to local operations.

Bob is setting out to make sure that you have a good understanding of the operational aspect of QFE but that is not to suggest that we should fly on QFE. Indeed, to do so presents a potential difficulty for the pilot as such an operation is contrary to AIP practice.

While the AIP does not reference QFE it is not evident from the Study Guide that this practice is not used in Australia.


You would need to address the SG question directly with Bob. I don't see that he needs to comment on local practice as he is just setting out to make sure that you have a familiarity with the particular Q-code. The fact that the AIP makes NO reference to QFE but prescribes, in numerous places, procedures using QNH, surely is prima facie evidence that local practice is not to use QFE ?

Today I phoned the AWIS at Kingroy (Elev 1492) and it gave me QNH of 1014. Then I phoned the Sunshine Coast AWIS (Elev ~ sea level). and it gave me a QNH of 1012. These airports are around 100NM from each other. So, theoretically, I will have used a QNH of 1012 if Kingaroy did not have an AWIS.

2 hPa difference in QNH in 100 nm appears to be quite reasonable. Other than for the internal workings of the way in which QNH is calculated, the elevation has little to do with QNH.

Alternatively, I may have asked a friend sitting in a plane on the ground at Kingaroy to give me the QFE QNH by setting the mainscale on his altimeter to 1492 and reading the 'QNH' (QFE) from it, which I would then use to dial into my Altimeter as I approach Kingaroy.

But, why would you ? You set yourself up for circuit conflict with other aircraft for a negligible benefit. The statement above seems to suggest that you don't appreciate the difference between QFE and QNH.

So, by using QFE I would have had an accurate reading in my approach to Kingaroy aerodrome.

Why do you suggest that flying with reference to QFE would be any more accurate than with reference to QNH ?

By using the QNH at Sunshine Coast, however, (1012) my Altimeter reading at an airfield with an elevation of ~1500 Ft would have shown a vastly different reading.

Not so. In both cases you would be reading an approximate elevation. So, at Sunshine Coast your altimeter would read something near sea level while at Kingaroy, it would read somewhere near 1490. Yes the readings are different, but that is only due to the fact that the elevations are different.

I think I see my issue here, ... I am bringing Pressure Hight into the equation, which I should not do.


Not that I can see. You don't appear to have made any reference to pressure height in this post other than for the last sentence.

In the end, the difference between 1012 and 1014 is not a lot. So, even if I had used the QNH for the Sunshine Coast airport it would not have made too much of a difference (say around 60 Ft or so).

That's fine. However, why wouldn't you have used, say, the forecast QNH or area QNH instead of a remote location QNH ?

I'm starting to wonder if you don't have a sound understanding of the difference between the three pressure levels and their interrelation with each other ?

Engineering specialist in aircraft performance and weight control.
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