barometric pressure vs. feild level pressure

[wingman1]

I was wondering if anyone could tell the difference between barometric and field level pressure, i am taking my ppl and reading up on the altimeter. In one of my text books it says you can adjust your altimeter to read your feild level pressure so as you land it will record 0 no matter where you are.

[iflyforpie]

The field pressure is the actual atmospheric pressure at the airfield. If you look at a manifold pressure gauge, that is what it reads with the engine shut down.

There is also the altimeter setting that will cause the altimeter to read zero at the airfield elevation. This is also known as QFE.

Barometric pressure is what the pressure would be if you dug a deep well down from the field elevation to sea level and measured the pressure. They don't actually do this (although my avionics teacher worked up a pretty good story to try and dupe us in school) rather, they use a formula to convert it from the field pressure. This is what the number after SLP refers to in a METAR. This is also known as QFF.

Don't confuse barometric pressure with the altimeter setting pressure. These are figured out different ways and in many cases the altimeter setting will be different than the barometric pressure to account for how the altimeter is calibrated. This is also known as QNH.

[E-Flyer]

There is also the altimeter setting that will cause the altimeter to read zero at the airfield elevation. This is also known as QFE.

The altimeter setting will read the elevation of the airport. It won't be 0 if the airport isn't located at sea level.

However, the Radar Altimeter will be reading 0, but that's AGL and not ASL like the Altimeter.

I was told by this guy flying for Finnair that the QNH is another calibration for the setting of the altimeter. It is read in millibars which is also the same decimal as hPa. If I'm not mistaken, QNH settings are used in most parts of the world.

[MichaelP]

Setting the QFE means the altimeter will read 0 when you touch down on the runway.
One reason a QFE is used is that the minimums can be the same for a number of airports with clear approaches. On an ILS this means a minimum descent height of 200 feet everywhere.
It also means that the circuit altitude of either 800 or 1,000 feet is the actual height above the airport.

The QNH is reported as "Q" on the American military airport weather reports.
It is the Sea Level Pressure and equates to the Altimeter Setting we use here.

There use to be a Regional QNH which was the lowest forecast pressure and was often a lot different to the actual QNH.
I used to set the local (actual) QNH for the aerodromes I was passing in Europe.

QFE, and QNH can be given in Inches, mb - hPa, or mm Hg.
QNE is standard pressure, 29.92", 1013mb, or 760 mm Hg.

In Britain they tried to say Hecto Pascals to everyone but soon went back to millibars... Why change what has been said for years... we do use BARometric charts don't we?

[monkeyspankmasterflex]

Eflyer

That a boy champ, don't let the fact that you don't know what the @#$! you're talking about get in the way of correcting others.

[E-Flyer]

Eflyer

That a boy champ, don't let the fact that you don't know what the @#$! you're talking about get in the way of correcting others.

I wasn't correcting anybody. I was rather clarifying that the "Altimeter Setting" a private pilot is going to come across everyday such as on the ATIS will not give him an indication of 0 feet if he's at an airport where the field elevation is "x" amount of feet AMSL.

Take CYYC and CYYZ. Your Altimeter will display two different values for the given Altimeter Setting at both airports. Calgary would show 3560 feet and Toronto would be closer to 580 feet.

No where was I stating that his explanation of QFE was wrong; from what I remember QFE is the air pressure that when set calibrates the altimeter to read the height over a field (AGL). Which when on the ground, would be 0. I just wanted to clarify to wingman1 that when he sets the altimeter, it will read the elevation of the field and not 0. However, when he sets QFE, the indication would be 0.

If you're for example taking off from an airport where there's no ALT SETTING. You set the altimeter to the elevation of the field, not to QFE unless it happens to be the case where the elevation is 0.

I'd love for you to tell me where I am wrong with this.

[wingman1]

Thanks guys, that information really helped. I'm finally able to move on from this subject. Appreciate it.