Nevada Altimeter Settings

[Crowman]

Hi All.

Sorry if this has been reported already in Nevada Map. I've noticed several aircraft suffer from the same issue, that is being unable to zero the altimeters on the ground at mission start they dont seem to be able to go low enough, dont think game error more of aircraft limitation, that could cause problems when flying in IFR conditions, also unable to change to Airfield setting for approach following info from ATC. something to bear in mind when flying through the Nevada Mountains in the dead of night with no NV.

[Yurgon]

I've noticed several aircraft suffer from the same issue, that is being unable to zero the altimeters on the ground at mission start they dont seem to be able to go low enough, [...]

 

I think I heard about this.

 

In which mission(s) does this happen? The airports in Nevada are relatively high above sea level. If the mission sets an additional low air pressure situation (making the altimeter show a higher value), it's quite possible pilots won't be able to set the altimeter to a reading of 0 at field elevation.

 

However, unless I misunderstand your point, this isn't actually a problem or bug with DCS - it's as real as it gets. ;)

 

I'd recommend to set QNH instead of QFE, i.e. set your altimeter to nautical height above mean sea level. So if Nellis was at 1,867 ft MSL, your altimeter should show roughly 1870 ft. Takes a little getting used to, but has quite a few advantages - among them the ability to get a valid altitude indication, even if it means you still have to do some calculations. Then again, 0 ft at the runway isn't equal to 0 ft in the mountains either, so without radar alt and/or NVGs, you always have to be aware of the terrain elevation anyway. :thumbup:

 

Edit:

 

I'm a huge fan of the following video. Back in the days before the Internet, videos were made in a way that people really, really understood everything after watching them just once.

 

Edited July 30, 2016 by Yurgon
Explanatory video added

[Sierra99]

Hi All.

Sorry if this has been reported already in Nevada Map. I've noticed several aircraft suffer from the same issue, that is being unable to zero the altimeters on the ground at mission start they dont seem to be able to go low enough, dont think game error more of aircraft limitation...

 

QFE is not used in the US. If you reference FAR 91.121 it will answer all of your questions about altimeter settings in US airspace. Basically you will be using QNH your whole time below 18,000 ft. I'm curious if this is part of the ATC fix for 2.x...

 

Sierra99

Edited July 31, 2016 by Sierra99

[Pikey]

I couldnt get low enough for the F5, was about 1k foot too high at the lowest baro setting. Seen this before, Hawk has it, can't recall others

[NeilWillis]

Does the altitude at which you switch from QFE to QNE (transition altitude) remain constant around the rest of the world? I have always presumed it is QFE + 5000 ft.

 

A useful (though I'm sure utterly inaccurate) set of memonics for the 3 commonly used altitude settings are:

 

QNH - Quantified Nautical Height (mean sea level - unadjusted for temperature)

QFE - Quantified Field Elevation (pressure setting for 0 feet altitude at an airfield)

QNE - Quantified height Nearly Everywhere (Standard Altitude)

 

There is a fourth I have come across, but it seems to play no real part in the way we measure altitude in DCS which is

 

QFF - (estimated mean sea Level Height adjusted for Temperature) I wonder if this will be needed when we get the Straights of Hormuz map? It isn't really relevant for NTTR as we don't have any sea on the map of course.

 

They are all really Morse Code Q Codes and as such have no recognised terms cionnected to them, and a full list of nautical and aeronautical ones can be found here: https://en.wikipedia.org/wiki/Q_code

Edited July 31, 2016 by NeilWillis

[Eddie]

The issue is "ATC" giving QFE, it shouldn't. Use QNH and you'll be fine (QFE is used for VFR in some countries, not IFR anyway).

 

QNH is most commonly used in military aviation, aside from a few specific cases.

 

And also, NTTR procedures are to keep Nellis QNH set for your entire time within the NTTR boundary, regardless of your altitude (including above 18,000MSL), another common military procedure known as force QNH.

Edited July 31, 2016 by Eddie

[NeilWillis]

I presume you are talking from a USA perspective Eddie? There is a different system used elsewhere.

 

That's why I said "in the rest of the world" as I know in US Military circles QNH applies to anything below 18,000 ft MSL.

 

In the UK, QFE is used below 5000 ft, and QNE above.

 

What unit is used when working with ground troops in US procedures? I'd expect the JTAC to supply QFE settings, is that correct?

[Eddie]

I presume you are talking from a USA perspective Eddie? There is a different system used elsewhere.

 

No, everyone uses the same system, it is international/NATO standard. However it does depend on local national ATC procedures in some aspects. QFE is often used for local altimeter settings in the UK/Europe for VMC. IMC requires QNH, wherever you are.

 

That's why I said "in the rest of the world" as I know in US Military circles QNH applies to anything below 18,000 ft MSL.

18000 MSL is US transition altitude for all traffic, not just military. Transition alt/level varies but the US has it unusually high.

 

In the UK, QFE is used below 5000 ft, and QNE above.

 

Only for VMC/local area, IMC and non local requires QNH in order to achieve terrain clearance. (it's no good knowing you're 100ft above your airfield when you're 50 miles away from your airfield flying toward a mountain 500 ft higher than your airfield).

 

QFE is useful for a visual approach to an airfield in relatively flat terrain, it can be dangerous for IMC and/or in terrain with significant elevation changes. RAF bases tend to be located in areas of level terrain close to MSL, and the RAF like most airforces operate primarily VFR where possible, hence we use QFE often. The USAF tend to operate from bases at higher altitudes and/or in non so level terrain, so use QNH almost exclusively.

 

What unit is used when working with ground troops in US procedures? I'd expect the JTAC to supply QFE settings, is that correct?

 

JTAC/FAC(A) supplies all elevations in MSL, QNH/force QNH is used. Force QNH is supplied by AWACS/other C2 agencies to ensure all aircraft in a given operational area are using the same altimeter setting regardless of altitude (you don't use QNE in the tactical phase of a flight).

 

From a weapon aiming point of view, QNH is required not only for terrain deconfliction but also to supply the fire control systems of many aircraft with accurate data (the A-10C for example requires QNH to be set on takeoff to calibrate the IFFCC).

 

In short QNH is far more commonly used than QFE in terms of amount of time over the course of a flight. In the UK as well.

Edited July 31, 2016 by Eddie

[rrohde]

QFE - Quantified Field Elevation (pressure setting for 0 feet altitude at an airfield)

 

When doing stop-and-goes at the same airport, it makes sense to use QFE as it gives you zero for your altimeter when you land, which makes it easier on you when not equipped with a radar altimeter.

 

My question: what do you do when you cannot set the altimeter to zero for that airport? Do you set it to the given elevation shown on the airport chart? I noticed that sometimes this wasn't possible in the NTTR missions either... what then?

 

Also. found this to be a nice writeup on the broader topic: http://code7700.com/altimetry_metric.html

[NeilWillis]

No, everyone uses the same system, it is international/NATO standard. However it does depend on local national ATC procedures in some aspects. QFE is often used for local altimeter settings in the UK/Europe for VMC. IMC requires QNH, wherever you are.

 

18000 MSL is US transition altitude for all traffic, not just military. Transition alt/level varies but the US has it unusually high.

 

 

 

Only for VMC/local area, IMC and non local requires QNH in order to achieve terrain clearance. (it's no good knowing you're 100ft above your airfield when you're 50 miles away from your airfield flying toward a mountain 500 ft higher than your airfield).

 

QFE is useful for a visual approach to an airfield in relatively flat terrain, it can be dangerous for IMC and/or in terrain with significant elevation changes. RAF bases tend to be located in areas of level terrain close to MSL, and the RAF like most airforces operate primarily VFR where possible, hence we use QFE often. The USAF tend to operate from bases at higher altitudes and/or in non so level terrain, so use QNH almost exclusively.

 

 

 

JTAC/FAC(A) supplies all elevations in MSL, QNH/force QNH is used. Force QNH is supplied by AWACS/other C2 agencies to ensure all aircraft in a given operational area are using the same altimeter setting regardless of altitude (you don't use QNE in the tactical phase of a flight).

 

From a weapon aiming point of view, QNH is required not only for terrain deconfliction but also to supply the fire control systems of many aircraft with accurate data (the A-10C for example requires QNH to be set on takeoff to calibrate the IFFCC).

 

In short QNH is far more commonly used than QFE in terms of amount of time over the course of a flight. In the UK as well.

 

Thanks for taking the time to explain that Eddie. It does make a lot of sense, but there is so much conflicting information out there.

 

I presume that the elevation information passed in a JTAC 9 line in DCS is target's height above mean sea level, hence the QNH altimeter setting?

[Eddie]

Yes a JTAC will pass MSL as that is what they have marked on their maps/GPS etc. The main point is that the MSL elevation of a geographic point is fixed (geological processes aside), and so setting your altimeter to provide MSL altitude (QNH) is the most effective in the vast majority of cases where terrain elevation is a consideration.

[NeilWillis]

Once again, thanks for the info Eddie.

[Art-J]

Just for a reminder, I would avoid talking about "everyone using the same system as international / NATO standard", because Russia (and post Soviet republics) did and still uses QFE as the standard in their military, and to some extent civilian ops, partially switching to QNH (civilian) in recent years.

 

I guess that's why ATC was programmed in DCS the way it was - correct for Caucasus map, but after simple porting it to Nevada map not making any sense now. Knowing that current ATC is a primitive placeholder before better one becomes available, I just don't pay much attention to it :D.

[Yurgon]

Lots of great information here, thanks everyone for contributing!

[rrohde]

This question still bugs me: In NTTR, I've sometimes get extremely low (or high, for that matter) altimeter settings for QFE from ATC, which are out of range and simply cannot be set (true for Creech and Groom Lake). What do you do in that case, considering that QFE is a viable setting for same-airfield stop-and-go practices, esp. considering A/C without radar alt readouts? Heck, most of the times I am not even able to dial in the field's own elevation because the altimeter settings are out of range (tested with the F-5E); Nellis seems to work fine... maybe local weather?

 

On weather: I've noticed that the weather in NTTR never gets quite warm enough compared to real life - could that be an issue, too?

 

Thanks.

Edited August 2, 2016 by rrohde

[ST0RM]

Something to consider is that within the NTTR, everyone uses 2992 as a common altimeter setting. We often flew in from our home base to refuel the players and upon entering the area, control advised us to use the common setting, despite being below FL180 at times.

 

Combined with radar altimeters and "hard decks", ground clearance can be maintained.

 

I've done the same in some MOAs.

[Eddie]

Something to consider is that within the NTTR, everyone uses 2992 as a common altimeter setting.

 

Perhaps previously, however now and for at least the last 3 years Nellis QNH is used for all traffic within the NTTR boundary, including traffic above 18000. You can verify in either the publicly available Nellis 11-250 or various non public sources.

[ST0RM]

Just flew there last summer. We used 2992 as a common setting. Shrugs...

[bcradio]

I hear them calling out the altimeter settings at various times around the ranges.

[Eddie]

Just flew there last summer. We used 2992 as a common setting. Shrugs...

 

Not saying you're wrong, however the RF and weapons school pubs and our aircrew who I quizzed on returning from RF last year and 16-01 earlier this year say different. What ex were you on, perhaps different procedure in place at the time?

 

The Lee corridor and other airspace surrounding Nellis does use standard US TA/TL though.

[ST0RM]

We were doing the A/R support for the C-17 WIC mass drop/airfield seizure.

 

No worries, it appears that mine were isolated cases. Thanks.

 

-Jeff

[Eddie]

It makes sense for multi engine to be using 2992 in that kind of ex I guess, it's not like you're particularly concerned with terrain in that instance. After all you're not going to be doing any weapon deliveries, low level evasion, or high speed abort manoeuvres.

[Piroflip]

I just read through this entire thread because I was wondering why I couldn't zero my Alt. at the field in NTTR just like the original poster. I even watched the old video on altimeter settings. Great stuff! I feel smarter already but, I think we haven't answered the problem which is how do you get height above the airfield on your altimeter in the NTTR map. Do you just have to set QNH according to the altitude of the airfield according to the editor and do the math in your head? Do you just rely on radar alt? If I'm missing something basic here, please let me know. I'm always willing to learn and understand. I think where this got confusing for me is flying Russian aircraft like the Mig21 or 15 where your alt. is displayed in meters and you have the altitude of the airfield in feet. Of course I know you can convert the alt of the field into meters but, it still seems overly complicated to get a zero level at runway indication. Thanks for all the input. Wait, I just thought of something else. Let's say you want to setup for pattern altitude approaching an airfield in the Mig21. How would you determine what the patern alt. should be and how do you make sure you compute that correctly in the aircraft?

Edited August 4, 2017 by Piroflip

[fenderplayer946]

With high elevation airfields it is not possible to zero the altimeter.

 

You've got it bang on with using QNH and correcting from there.

[Piroflip]

Thanks fender. I'll keep practicing with it.