QNH vs. inHg...

[Steen Jorgensen 1187013]

I'm flying a B737 around Europe, and QNH is constantly given in hPa, but the altimeter in the Boeing is in inHg. Do you guys constantly convert with a calculator on the fly? And is this what real-world pilots do, too?

 

Best regards,

Steen

[Simon Kelsey]

Hi Steen,

 

Which B737 are you flying?

 

Real aircraft (and most decent FS models) are equipped with EFIS systems which can be switched by the pilot from inHg to hPa, or airliners with old style clockwork instruments usually have both subscales on the altimeter (light aircraft based outside the USA will often just have hPa on the subscale). Certainly the primary scale used in the region the aircraft is based will be available.

 

InHg is only used in North America and some places with a US influence (e.g. some Pacific territories etc) - the rest of the world uses hPa.

[Ross Carlson]

The outer part of the BARO knob on the EFIS control panel lets you switch the altimeter setting units. (May or may not be modeled in the specific 737 you're flying.)

[Steen Jorgensen 1187013]

Interesting! I'm flying the x737 for X-plane 10.

[Brad Littlejohn]

Hi Steen,

 

Which B737 are you flying?

 

Real aircraft (and most decent FS models) are equipped with EFIS systems which can be switched by the pilot from inHg to hPa, or airliners with old style clockwork instruments usually have both subscales on the altimeter (light aircraft based outside the USA will often just have hPa on the subscale). Certainly the primary scale used in the region the aircraft is based will be available.

 

InHg is only used in North America and some places with a US influence (e.g. some Pacific territories etc) - the rest of the world uses hPa.

 

It's actually more of a North America thing than just the USA. Canada and Mexico also use inHg instead of hPa, so you'll hear this up north as well as down south and their related territories.

 

Most panels should have both of these listed, especially if on a modern-day aircraft (they had both listed in FS9, so I know anything newer than 2004 should have it), but if not, a simple formula would be:

 

QNH * 2.954 = InHg

InHg / 2.954 = QNH

 

That should get you roughly what you need. Obviously round up or down to what ATC tells you, or relative to the METAR/ATIS/AWOS for the field in question.

 

BL.

[Dace Nicmane]

It is modeled in the x737. Make sure the cursor arrow is pointing left or right.

[Matthew McEwen]

Since the question has already been answered, allow me to clarify a few things to be precise.

QNH means "local altimeter setting", it is not a unit of measurement.

inHg is one unit of measurement used in North America & Japan.

hPa is another unit of measurement used in the entire rest of the world (except...)

The odd one out is mmHg, millimetres of mercury, used only in North Korea. Whoever came up with that should be shot (/opinion).

But in any case, ([Mod - Happy Thoughts]uming you're using ICAO phraseology) no matter which unit you use to refer to the local altimeter setting, you call it QNH, and then if necessary, specify the unit after, i.e. "QNH 1003 hectopascals" or "QNH 29 62 inches". Using ICAO phraseology, never say "altimeter" to refer to QNH.

[Andreas Fuchs]

The odd one out is mmHg, millimetres of mercury, used only in North Korea.

And Russia. All ATIS that I have come across in Russia also state the local altimeter setting in Millimetres of Mercury, next to QFE and QNH.

 

When you hear "QNH" this will normally tell you that it is a setting HPA. When you hear "altimeter" it will be the local altimeter setting in INHG. That's how it works in the real world.

[Matthew McEwen]

When you hear "QNH" this will normally tell you that it is a setting HPA. When you hear "altimeter" it will be the local altimeter setting in INHG. That's how it works in the real world.

 

That's actually not true. The phrase 'QNH' is the only way to refer to an altimeter setting using ICAO phraseology. The dilemma here, however; is that we're looking for a place that A) uses inches; AND B) uses ICAO phraseology. The only whole country I'm aware of that meets both of these criteria is Japan. There's also 1 aerodrome in Kenya that uses inches. And in both of these places, in the real-world & on VATSIM, you'll hear them say 'QNH' and give the QNH in inches.

 

Listen to

or

and you'll hear it say something like "QNH 3007 inches". Also if you listen to liveATC in Japan you'll hear them say something like "descend 11,000, QNH 3014 inches".

[Andreas Fuchs]

Matt,

 

true or not true: it is how it works in the real world. Apart from Japan and some "isolated aerodromes" the general rule that I have stated above works in the real world and also here at VATSIM. In the case of "QNH 3014 inches" it will be clear to any pilot that it is not possible to dial in "3014 HPA" on the instruments - problem solved. Let's please use some common sense and especially for beginners it is very important to have some rule of thumb. The one that I am also using at my job in the real world is the one as above. I am used to flying all three systems on a regular basis: QNH in HPA, QFE in HPA and "altimeter setting" in INHG.

 

I hope you can now better understand why I wrote what I wrote.

[Robert Shearman Jr]

I'm with you, Andreas. I found that when writing training material for a VATSIM ATO, I had to be really careful about wording, because inevitably I'd get an email on every lesson from someone who felt it necessary to point out the exceptions to each rule. I think it's more than fair to say that, GENERALLY and with a few exceptions, "Altimeter" nearly always refers to a setting between around 28.50 and about 32.00 inches of mercury, and "QNH" nearly always refers to a setting between approximately 965 and somewhere around 1065 millibars AKA hectoPascals. Normally. Most of the time.