Difference between QNH & QFE?

[RPRIEVER 52]

Greetings all,What is the difference between QNH and QFE? On the MD-11, you can choose between the two, and the PFD changes a bit, but what exactly does each one mean and how do they differ?Many thanks,Ron Priever

[flightjimbo123 0]

QNH & QFE are two of the many remaining Q codes from back in the day.QNH = represents ALTITUDE above Mean Sea LevelQFE = represents your HEIGHT above the aerodrome from which it is measuredeg: Airport elevation is 400ft above sea level If you set the QNH on your altimeter then it will read 400' If you set the QFE on your altimeter then it will read 0'Hope this helps,James Harris

[Chock 17,769]

The easy way to remember the difference is to think of them like this:FE = Field ElevationNH = Nautical HeightAl

[Check_Airman 3]

The easy way to remember the difference is to think of them like this:FE = Field ElevationNH = Nautical HeightAl

AHA!!!That's what the NH stands for. Although technically, shouldn't height be measured above the terrain (eg DH)? Why not QNA for Nautical Altitude?Paul

[pdavies 0]

Always learning something new! This topic is usually confusing.Qfe is used most frequently in Europe, Asia, well, probably everywhere else except the United States.Qnh is used in the United States, but is not CALLED Qnh. The reason we all struggle making this connection is in the US Qnh is given in inches of mercury, where in most of the rest of the world it's given in Hectopascals, or millibars.The altitude that the altimeter yields (0' and 400' as referenced above) will only be true while on the ground, not in the air. So, if we are landing under Qfe, the altimeter will say 0' when we touch down, despite being 400' mean sea level (MSL). Qfe therefore, represents, roughly, above ground level (AGL) while Qhn represents MSL more closely.Oddly enough I referenced Wikipedia (who knows if it's true) which states that Qnh stands for "Quasi-Non-Hydrostatic", "Nil Height", and "Nautical Height". Take your pick, ladies and gentlemen!

[3-2-1-Now 126]

QNH is used in Europe! QFE is only used if doing circuits around a particular airport as QNH covers a larger, general area. QFE is not suitable for terrain clearance.QNH is also corrected to the LOWEST pressure reported for an area to ensure that aircraft miss the terrain, as the pressure over here might not quite be the same as the pressure over there where that big hill is. This is also the reason why transition altitude varies. Transition altitude accounts for the highest terrain in the area. It is 18,000 ft in the US to allow for the Rockies for example.If the set pressure on your altimeter is lower than what it actually is outside, you end up higher relative to the ground. e.g. 1013 hPa outside, you set 1000 hPa then fly at 1,000 ft as per yuor altimeter, you will actually be a bit higher than 1,000 ft.When speaking the pressure over the radio, you say "QNH 1-0-1-3" or "Altimeter 2-9-9-2", to differentiate between hectopascals and inches mercury.QNH actually means "Quasi-Non-Hydrostatic".There is also QNE (pressure altitude), but it is only used for performance planning usually.Best regards,Robin.

[downscc 1,327]

It is 18,000 ft in the US to allow for the Rockies for example

I find this interesting. I had always assumed it was because that was the base of the old positive control airpace, where everyone had to be on a flight plan because of the crash over the Grand Canyon a long time ago. Air traffic control was based on flight strips (which is still used as a backup for radar outage). The terrain clearance objective makes sense, maybe too much so for a government solution.

[Chock 17,769]

That is actually not correct about QNH being short for Quasi Non Hydrostatic. QNH is one of many Q codes, the Q codes originally being a list of common nautical phrases that were abbreviated to three letters to facilitate morse code brevity, although it was actually the UK Postal Service that were mainly instrumental in it development, since at that time they were involved in overseeing wireless telegraphy as well as delivering mail. The reason they begin with Q is so that an incoming morse message that commences dash, dash, dot, dash (i.e Q) is easily recognisable to the ear, and since it is rare for words to commence with a Q in the English language, it was considered a good choice as a message identifier when the code was being developed. Most explanations as to what the code letters stand for have grown up around convenient mnemonics which were thought up long after the fact.Al

[vololiberista 205]

The origin as stated is for use in morse code transmissions as queries hence the "Q"QFE What is the atmospheric pressure, at aerodrome elevation, at ...(place)QNH What should I set on the sub-scale of my altimeter so that the instrument would indicate my elevation if I were on the ground at your station. Also adopted by the ARRL, for use only in CW nets, as meaning "Your net frequency is high".The first one gives the true atmospheric pressure at a given place. Thus setting your altimeterto QFE will give you zero altitude on the ground at that particular location. In the UK you are given the QFE by the tower so that your altimeteris set correctly for both the approach, circuit and let down. It's very important at places like Biggin Hill. There have been a number of accidents theredue to pilots not setting QNH and therefore arriving in the circuit 500+ feet lower than they should be!!!The second is obvious and in the UK there are regional QNH reports thus one knows how much higher one should fly to avoid terrain or obstaclesIt's about time that N. America fell in with "the rest of the world!" and gave up inches and to have such a ridiculously high transition altitude which isn't neccessary if regional qnh is in use.

[downscc 1,327]

It's about time that N. America fell in with "the rest of the world!" and gave up inches and to have such a ridiculously high transition altitude which isn't neccessary if regional qnh is in use.

Gee, I wonder what percentage of world flying is done in N. America? More to the point, we don't use regional QNH. While enroute below FL180, center will provide an altitmeter setting from an airport within 50 nm and that ususally doesn't change until handoff to the next controller; however, we always use airport altimeter (ATC, ASOS or ATIS) for terminal operations, not regional settings.The transition height works just fine, we are allowed VFR rules below it and not allowed above it. No way would we be happy about having to fly IFR at levels below 18000.

[vololiberista 205]

Gee, I wonder what percentage of world flying is done in N. America? More to the point, we don't use regional QNH. While enroute below FL180, center will provide an altitmeter setting from an airport within 50 nm and that ususally doesn't change until handoff to the next controller; however, we always use airport altimeter (ATC, ASOS or ATIS) for terminal operations, not regional settings.The transition height works just fine, we are allowed VFR rules below it and not allowed above it. No way would we be happy about having to fly IFR at levels below 18000.

Quite a lot of flying is done outside North America!!!! And bear in mind that an American Pilot's Licence is not valid in the UK

[pdavies 0]

Well here's another way of looking at it: in FS we can hop countries effortlessly, and probably a good chunk of people here on the PMDG forums use our planes to fly internationally. In real life, however, the majority of pilots stick to their own country, so differing rules for transition altitudes is a moot point. The only people that encounter different regulations are airline pilots and corporate pilots who fly internationally and maybe a very small percentage of general aviation pilots that fly over borders.I agree with Dans post entirely - I think having a transition altitude lower than 18,000' is silly talk. That really keeps things open for private pilots who aren't instrument rated.

[3-2-1-Now 126]

+1I like the US system.Look at what NATS did recently to the ATC services in the UK!! It seems more complex than it needs to be, and all in the name of avoiding LIABILITY.Best regards,Robin.

[Avantime 81]

Think:Meters/QFE = Russia+North Korea+CIS e.g. KazakhstanMeters/QNH = China+VietnamFeet/QNH = Rest of the worldTraining is required for Western crews going into QFE airports, and the same for Russian crews in QNH airports. Metric altitudes have been used for ages and will continue because their air forces' aircraft only have metric altimeters. Also think measurements:Inches of Mercury = USA (And Canada I think), Hectopascals (HPa) in rest of the world.Standard Atmosphere e.g. Flight Levels = 29,92 in.Hg or 1013.2 HPaSome countries have transition 'altitude' i.e. 18000. Other countries have transition 'levels' e.g. 11000ft to 13000ft.

[DavidP 1,410]

In Australia, since our highest mountain is in the region of 8000', we have a transition altitude of 10000' and a transition level of FL110.We conduct plenty of IFR below 10000'David