Altimeter

[Little Dump]

I've read that the altimeter needs to be reset depending on where you are in the world and how far above sea level.

I'm wondering if someone could explain this to me more.

Also wondering if FS9 handles this altimeter setting, or if I have to change it depending on my departure location.


Thanks

[Edam]

You set it to 29.92 over 18,000 feet.

[Little Dump]

What about on the ground at an airport. How do I know the right setting?

[JSkorna]

Press the "B" key.

Hope this helps,
Jim
ActiveSky Support
http://www.hifisim.com/images/as2004proudsupporter.jpg

[Little Dump]

anyway I can do it by myself?

and can someone explain why I have to do this?

[lnuss]

Why is simple, sort of: The altimeter is nothing but a specially calibrated pressure instrument, with a limited correction ability built in for manual use.

I'm sure you've heard the weatherman give barometer readings -- they are indications of how much pressure the atmosphere is exerting: 29.92 inches of mercury at sea level under standard conditions, that is, 59º F and 0% humidity. As the aircraft climbs, the pressure drops with altitude, as does the temperature, such that the standard temperature at 5,000 ft. is 41º F, and the actual barometric pressure will be somewhere around 23-24" of mercury (Hg). However, even at Leadville, CO, elevation just over 10,000 ft above mean sea level (MSL), a barometer reading (or an altimeter setting -- same thing) is given as corrected to sea level, so the standard altimeter setting will still be 29.92" Hg.

As the temperature rises, humidity increases, or barometer reading decreases, the air has less actual pressure. Obviously the pressure rises as these factors go the other direction. And pressure will rise with a descending aircraft.

So the altimeter setting is given by a ground station which can observe the pressure changes that have occurred and can figure a correction to give the pilot.

In the U.S. only one type of altimeter setting is given -- the barometer reading corrected to sea level. When that value is set into the Kollsman window, the little window that is (usually) on the right side of the altimeter, with the knob on the bottom of the altimeter, then the altimeter should read field elevation when the aircraft touches the ground, and the aircraft's altitude should match that of any other aircraft with the same reading on the altimeter and the current "altimeter setting" applied.

In the UK, and perhaps other places, they have another type of altimeter setting, which is intended to have the altimeter read zero when the aircraft touches down, assuming that the touchdown point is at the same elevation for which the correction is given.

FS matches the real world in this respect, so if you have an erroneous altimeter setting, then your altitude indication will be wrong. If you don't want to use the "B" key to reset the altimeter, then you can use the mouse with the knob at the bottom of the altimeter and adjust the Kollsman window yourself.

[Little Dump]

So in the sim how do I know what to adjust to? I'm assuming I either have to find out barametric pressure (how do I go about this) or figure out field altitude above seal level (also how do I go about this)

Thanks

[someone]

Tune a nearby airport's ASOS/AWOS/ATIS and it will give you the local altimeter setting. In FS if you hit the "B" key it will automatically set it to the current setting. If you're on a flight plan or getting flight following, the controllers will give you the local altimeter setting whenever you are handed over to a new controler.

If you are at an airport without ASOS/AWOS/ATIS, just set the altimeter to read that airports elevation above sea level. Unless flying IFR, I usually just set the altimeter to read the correct altitude at the airport before departing. Then before landing, I'll check a local ASOS/AWOS/ATIS for the local altimeter setting.