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tom9909

ATIS and QNH

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Hi Guys

 

Firstly I am new to flight in general but eager to learn. My problem is when I listen to ATIS at any airport its telling me to set my QNH to an altitude that I think is incorrect for the airport. For example ATIS at YSTW (Tamworth Australia) says to set QNH 1013 which puts me at an altitude of 1340 when on the ground? would I not crash is using ILS when landing with these settings.

 

I am sure I'm not understanding something correctly hopefully you guys can help

 

Thanks :)

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On a side note as I am not an expert on QNH if you want to cheat a bit you can set it by pressing "b" on the keyboard - sets it automatically for you - I like easy

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"The airport resides at an elevation of 1,334 ft (407 m) above mean sea level." (quote from wikipedia)

 

There is nothing wrong here... what you are doing is correct.

 

"would I not crash is using ILS when landing with these settings."

 

You wouldn't.  The ILS is a pair of radio beams you follow down to its (antennas) on the ground, so if you were established on the ILS (in theory) it doesn't actually matter what the altimeter reads, as long as you kept the instrument centered you would get down.  In reality, the airport elevation is on the approach chart, and pilots account for this when landing.

 

There's quite a bit more to QNH / altimetry, but hope the above (simplified and brief explanation) is a start to answering your question.

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QNH is the local area pressure setting (displaying the airfield elevation above sea level when on the ground). Referred to in communications as ALTITUDE.

 

QFE is the airfield pressure setting (displaying ZERO when on the ground at the airfield). Referred to in communications as HEIGHT.

 

Unfortunately you can only "set" QNH in P3D (also via "b" button on keyboard as Rich says).

 

Always check the destination airfield elevation before departing. Then you'll be able to mentally calculate your circuit height on approach. So at ie Tamworth with a height above sea level of 1340 ft your circuit altitude is likely to be 2340 ft (local variations may apply - I don't have a chart for Tamworth to hand ;)

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Thank you everyone for your help I think im starting to get it. QNH is the elevation of the airport above sea level and the altimeter will represent this when set to the local QNH and on the ground  :P as you said you need to calculate the difference whilst flying.

 

Thanks everyone

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Unfortunately you can only "set" QNH in P3D (also via "b" button on keyboard as Rich says).

 

Hmm did not know that - thanks for the info - guess I'm good to go

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Hmm did not know that - thanks for the info - guess I'm good to go

 

You can of course set the OFE (height above airfield) by just setting your altimeter to ZERO when on the runway. That is then the local airfield QFE. This is useful if you're staying within the circuit for training etc.

 

The only problem doing this means that you may get a warning message from the sim telling you to set your altimeter correctly (to QNH). Not sure if this still appears in P3D. It used to bug me in FSX!

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On a side note as I am not an expert on QNH if you want to cheat a bit you can set it by pressing "b" on the keyboard - sets it automatically for you - I like easy

 

Which is fine for the default ATC which thinks that the whole world has a transition altitude of 18000 feet which is what the "b" key defaults to.

But that will quickly get you into problems when flying outside of the USA with Radar Contact or online ATC where the correct TA/TL's are used.

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