QNH and QFE

[ClausHoffmann]

While constructing a training mission for navigation on the NTTR map I stumble on a problem I cannot understand. In the Mission Editor under the weather settings the QNH is set to 29.92 inHg. It is my understanding that this means, if altimeter is set to this value, it will show an altitude of zero.

In the mission the tower in Nellis gives me a QFE of 28.06 inHg. This value cannot even be dialed into the altimeter of the F/A-18C Hornet. 28.10 inHg is the minimum to be dialed in and then the altitude is shown as close to zero. In fact Nellis AFB is roughly 1.850 ft high. This should be shown on the altimeter.

What am I getting wrong here? Thank you very much for your support.

[iFoxRomeo]

QNH gives your altimeter the reference to mean sea level. So if you set the QNH you would only see 0ft when you´re swimming on the water.

 

 

QFE would show you 0ft when on the runway. But at the elevation figures in NTTR not many altimeters can set the required values.

 

 

Fox

[ClausHoffmann]

Okay, thank you. I mixed up the terms obviously. Still I am wondering, why ATC in Nellis gives me the QFE, which is not of use for anything and cannot be dialed in in the jet anyway.

[Hippo]

QFE gives you your height above the runway.

 

I don't know what the USAF does IRL at Nellis or elsewhere, and I'd certainly be interested to know (QNH?).

 

I think QFE is used by some airforces around the world (e.g. UK RAF), and for some reason ED has hard coded using QFE into the game's ATC, and so we're stuck with it (for now). Clearly you'd not have the same issue at the Caucausus airbases. Still, it's a curious choice, since using QNH is much more common throughout the world.

 

 

*EDIT* From a quick browse around, it seems that QFE is used in Russia, so that explains the ED choice.

 

For Nevada, I would just dial in the QNH into the altimeter instead (available from the briefing iirc, or just dial in the airfield altitude from its chart).

 

 

*EDIT* And it seems that I Don't RC. QNH is not given in the briefing (althought it really, really should be) - sorry.

 

 

*EDIT* PS Shamelessly copied and pasted from elsewhere:

 

1 inch mercury is approximately equal to 900 feet. This calculation is therefore also approximate but is good for airfield elevations to several hundred feet since we round to the nearest hundredth inches.

Divide the airfield altitude in feet by 900 to get the number of inches above MSL. Add this to the QFE to get QNH or subtract it from QNH to get QFE.

For example, the airfield elevation is 300 feet. Diving by 900 gives us 0.33r. The QFE is 30.12. Add 0.33 to get 30.45 which is the QNH.

If the airfield elevation is below sea level, subtract rather than add and vice versa.

Edited January 11, 2020 by Hippo

[Yurgon]

Still I am wondering, why ATC in Nellis gives me the QFE, which is not of use for anything and cannot be dialed in in the jet anyway.

 

It's ancient DCS behavior. And you're right, with most of the Nevada airports QFE can't even be dialed in.

 

For now I guess we have to accept it. But today's newsletter mentioned the ongoing plans to implement a new ATC for land based airfields. I'm pretty sure the old QFE-problem will be revisited with the new ATC.

 

Plus, they mentioned improved weather, dynamic weather and weather/pressure fronts. In a more dynamic environment, we might finally get to see a real pressure difference across the maps and over time.

 

In any case, as long as the mission uses Static Weather, I believe the air pressure will be static across the entire map, so you can just dial in QNH before takeoff, maybe take a note of the pressure setting in case you transition to standard pressure/flight levels, and then dial that same QNH back in before you land. Should be close enough for most cases.

 

There's also the possibility to calculate QNH from QFE and vice versa for a given altitude; I don't have a formula at hand, but that should be easy enough to google. So if you have dynamic weather, bad visibility and you really need a proper QNH, you could still calculate that from the QFE that the tower gives you.

[DarkFire]

I'm hoping with the new ATC coding we'll get the option of full METAR reporting. That way everyone will be accommodated - QFE for VKS & RAF, QNH for our USAF & USN friends.

 

I'm vaguely amazed that NATO didn't standardize on one pressure reading standard.