Can you help a student out here with "Q codes" (QNE, QFE, QNH, QFF)

LongRoadBob

LongRoadBob

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I think I have a handle on QNE, QFE, QNH, but I am puzzled by QFF.

If I understand correctly, my instinct (which must be wrong) is that QFF must be the most correct setting for the altimeter because it is most in tune with "reality"

Let's see if I have this right...(paraphrasing)

QNE = whatever the altimeter reads when one sets the kollsman window to the ISA...either 1013.2 hPa or 29.92" mercury. Either way I see the advantage I think in that at flight levels everyone (all aircraft, no matter what the reality of the atmosphere are flying agree on hoe you find out what height you are?) is using the same measure.

QFE = adjust the altimeter so that the field elevation at the airport you are taking off from is 0 feet. I can see how this might be useful in some instances, I think, not sure.

QNH = The most commonly used setting for the altimeter...the one you get from INFORMATION, or contact with towers, etc. (am I wrong here?) which is what one sets on the kollsman window for sea level but which is dependant on the ISA (international standard atmosphere) which assumes a constant decrease in temperature, decrease in density, humidity, and air pressure per a given change in real altitude. It is an ideal, which we all accept but is divorced from reality.

So we come to...

QFF which from what I am reading in the ground school book is the actual air pressure adjusted to the actual pressures and temperatures that are existing at that particular time and place. It takes into account the actual conditions and is used (according to my book) by meteorologists for mapping actual conditions for being able to sudsy the weather...but also that it is not used except in special circumstances (they don't say which) and has gone out of practice.


So are the things....

1) am I missing the point or misunderstanding the q-codes?

2) as a dumb newbie, I would expect that I would want to set my altimeter to QFF for the most accurate readout possible on the altimeter. Why don't I want that? I can understand using QNE so that at the higher levels we all are on the same page no matter what, and I think I can understand QFE (although I am uncertain and would love to hear from real pilots when that is the thing to use) But QNH bothers me a lot. I see it as an assumption that is abstract and not nec. realistic, where QFF would be more correct.

Obviously I am missing some point here, but I have tried to figure out what it could be and I haven't been able to so far. It might be that QFF costs more to determine, I don't know.

I really would appreciate any help here, either with my possibly misunderstanding the "Q-codes" or with why they are as they are used. How they are really used in normal VFR flight? My thoughts also go to the idea that with VFR (all I can even possibly handle right now) you have to be able to judge height and all No matter what the altimeter reads.

Thanks for any criticism, help, or comments.
 
Most of us here won't be able to answer that as about the only place you find Q codes around here are military bases. We pretty much only do one of two things: set the altimeter to ATIS/AWOS/What ATC gives us, or set it to field elevation when we are at fields without AWOS/ASOS/ATIS.
 
EdFred said:
Most of us here won't be able to answer that as about the only place you find Q codes around here are military bases. We pretty much only do one of two things: set the altimeter to ATIS/AWOS/What ATC gives us, or set it to field elevation when we are at fields without AWOS/ASOS/ATIS.
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Thanks, but as an experienced pilot, do you have any insight into why QFF isn't used?

The Q codes are in the ground school material and here in Norway they are part of the written exam. I need some help. I can (and will) ask both my CFI and the school, so I can find out about this, but just thought that with so much knowledge here I might get an insight.

Thanks for the reply!
 
Translating, I see QNE = "pressure altitude," and QNH = "indicated altitude."

Those are the only ones you use for your altimeter.

Other altitudes in use in the US are "absolute altitude" (AGL), which approximates QFE (it's not the same because the rate of change is different for nonstandard temperature) and is relevant for terrain and obstacle clearance, and "density altitude." The latter does not appear to be QFF, and it's relevant for your aircraft performance.

Most of the meterological data I've dealt with has just been in QNE. It's just pressure altitude. Occasionally, I see geometric altitude used, but not in the global models. In fact, GFS has a field for the geometric altitude as a function of pressure altitude (i.e., it's backwards).

These Q-code terms are not commonly used in aviation in the US.
 
I've always understood it as:
QNH - Nautical Height (Altimeter adjusted for pressure)
QFE - Field Elevation (Altimeter set to 0)
QNE - Standard (29.92", for use in the flight levels)
 
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Cpt_Kirk said:
I've always understood it as:
QNH - Nautical Height (Altimeter adjusted for pressure)
QFE - Field Elevation (Altimeter set to FE)
QFF - Standard (29.92")
Click to expand...

Isn't that last one QNE? My understanding was QNE is when you set the kollsman to standard ISA sea level, 29.92" (or 1013.2hPa)
and that QFF is ajusted somehow to factor in temp, density, pressure, ???
 
QFE - In your original post you put FE = 0, I think you would mean FE = Whatever the known Field Elevation is?

Only time I would think setting the altimeter to 0 at a FE other than 0, would maybe be for Aerobatics at an airshow?
 
Seems as if they used QFE in Russia. These terms are also more common internationally which would make sense since the OP is in Norway.
 
ifly4fun said:
QFE - In your original post you put FE = 0, I think you would mean FE = Whatever the known Field Elevation is?

Only time I would think setting the altimeter to 0 at a FE other than 0, would maybe be for Aerobatics at an airshow?
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Actually as I understand it if you set the height of the airfield on the altimeter so it reads correct, you are setting QNH, just in a backwards way but it should be pretty close to ISA.

QFE according to my texbook would be 0 at field elevation. They say it in a roundabout way, but they say directly that on landing at the same field you would expect then it to be showing 0. It shows the actual height over that field.
 
LongRoadBob said:
Actually as I understand it if you set the height of the airfield on the altimeter so it reads correct, you are setting QNH, just in a backwards way but it should be pretty close to ISA.

QFE according to my texbook would be 0 at field elevation. They say it in a roundabout way, but they say directly that on landing at the same field you would expect then it to be showing 0. It shows the actual height over that field.
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I've seen a small number of people try that, so pattern altitude is 800 or 1000 or whatever. Seems like a really bad idea, since almost all publications use MSL and it isn't hard at all to exceed your altimeter's range of adjustment. Lots of airports are over 2000 MSL.

Real life is NOT close to ISA. If you take ISA too seriously, it's 15 C at the North Pole in winter, and in Death Valley in summer. And there is no weather.
 
Q codes are readily available by searching. Here is the wikipedia list. I haven't vetted them to know if this list is accurate.

Aeronatuical Q codes used to be used when most aeronautical communication was via CW. I've never run into them. We still use a few of them regularly in amateur radio, both in CW and phone.

https://en.wikipedia.org/wiki/Q_code
 
Easy way to remember them...

QFE - FE="Field Elevation". Set QFE and the altimeter reads zero when at field elevation. Rarely used in the USA.

QNH - NH="Near Home". QNE is is local (i.e. near home) altimeter setting.

QNE - NE="Nearly Everywhere". 29.92 which is used "nearly everywhere" above the transition altitude.
 
LongRoadBob said:
Actually as I understand it if you set the height of the airfield on the altimeter so it reads correct, you are setting QNH, just in a backwards way but it should be pretty close to ISA.

QFE according to my texbook would be 0 at field elevation. They say it in a roundabout way, but they say directly that on landing at the same field you would expect then it to be showing 0. It shows the actual height over that field.
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Ahh makes sense.. I guess if you're relying on this you better hope the pressure doesn't change much during your flight. I've done 99% of my flying at airports that are <50' MSL, so i've been spoiled at always shooting for 0 on landing. When I get out of the local area, it always adds some math that I don't typically have to deal with.
 
ifly4fun said:
Ahh makes sense.. I guess if you're relying on this you better hope the pressure doesn't change much during your flight. I've done 99% of my flying at airports that are <50' MSL, so i've been spoiled at always shooting for 0 on landing. When I get out of the local area, it always adds some math that I don't typically have to deal with.
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Better to do the math.

I've yet to see an altimeter that can be set below 28 inches. 29.92 at 2000 MSL is pretty close to that. There are lots of airports above 2000 MSL.
 
I learned to fly using Q codes and was surprised they were not used for private aviation in the US.
 
ifly4fun said:
Ahh makes sense.. I guess if you're relying on this you better hope the pressure doesn't change much during your flight. I've done 99% of my flying at airports that are <50' MSL, so i've been spoiled at always shooting for 0 on landing. When I get out of the local area, it always adds some math that I don't typically have to deal with.
Click to expand...

I'm getting the idea that one always uses margins for obstacles, and lands using eyes on the outside...with a slight check maybe inside here and there on the glide but the last part of the landing is by eye, judgement, etc. am I wrong in that? Again, I'm a total newbie, know nothing...I had my second takeoff last week, which was the first takeoff I knew for sure it was all me at the controls. A really exciting thing for me.

Also learning about instruments and Q codes and seeing how my instructor shows me, we set the altimeter during the checklist to the airports known altitude (class G? I'm not sure yet, but no tower and no air pressure information) until we get to the practice area where we contact control for that area, and are given QNH. We then set to that in the kollsman window. Still, learning about how the instruments work, and that it is based on ISA makes me think it is still my eyes outside the aircraft that are the final judge because it can't be totally trusted, at least by me until I learn more, like IFR or just more even with VFR.

...and I would not be averse to anyone letting me know if my viewpoint here is not right. In the end I will listen to and trust my CFI on points like these, but I am an open book at this point, a mostly empty one.
 
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