Further Altitude Adjustments Questions

So, I am new to the forum here and I have been doing the flight sim stuff for quite a bit. Off and on just a couple of years. While the majority of that time was just out of complete boredom and consisted of me just getting into an airplane and flying some place on GPS, the last several months I have kinda taken this serious turn towards actually learning more about what the heck I am doing. It has actually opened my eyes to a lot of stuff on FSX.

 

Anyway, my question is about setting and calibrating the altimeter. Normally, all of my flights are in the "clear weather" settings, however, yesterday a I made a short flight from Tulsa, OK to Witchita, KS in stormy weather. As soon as my plane loaded up, there was a tip of some sort that popped up on the screen letting me know that I needed to set my altimeter, which it had never done that before on any of my other flights.

 

That spurred me into searching for answers on the web, which lead me to the aged forum post on here https://www.flightsim.com/vbfs/showthread.php?182676-Altimeter-settings . It was helpful and I got some extra information out of it.

 

However, I am curious about a couple of other things:

 

1- Did that popup suggestion come up only because of the weather, and I then should have had to reset the altimeter (by pressing "B" or manually doing so by listening to the ATIS altimeter setting and twisting the altimeter knob?

 

2- What about while actually in flight? Like, if I notice that in the middle of my flight that (because of weather or just even location) that the ATC says an altimeter reading that is different than what I have set, do I go ahead and set it to that?

 

3- Is it a good idea to regularly check with airports that I am passing by on my way to another airport (during a long flight) to see what their altimeter is set at?

 

4- So, at the end of my flight that I was describing above, something odd as heck had happened. Throughout out the flight, it looked like the ground was quite a bit closer to the aircraft that every before, even after take off and reaching my cruising altitude. When I tuned the elevation on the auto pilot (Using a Cessna Caravan, and my cruising altitude was 5,300) down to 2,500, I seriously would have gone right down into the ground if I didn't notice it and pulled up. Still getting back to 5,300 seemed VERY low.

 

Was this because of the change in the altimeter setting? I could have swore that I pressed "B" when it told me to right when the flight loaded up the airplane, so maybe I didn't actually do it? Or maybe it needs to be changed multiple times during flight? If it does need to be changed in flight, what is the strategy that you do?

 

Thanks for bearing with this whole question. Figure this place would be a really good source for answers.

 

Stedman

When flying in Real Weather conditions you will be resetting your altimeter occasionally. Always follow ATC when they give you an altimeter reading. Be sure to have your Pitot Heat on when flying in stormy conditions.

Some basics.

Barometer measures air pressure.

I have a simple dial-barometer hanging on my wall. I think many people have one.

When the weather worsens I can generally see the air pressure dropping.

Air pressure is lower at altitude. On top of a mountain the air pressure is much lower.

But not only on top of a mountain, but everywhere in the sky.

The higher you get, the lower the air pressure.

The altimeter is no more than a barometer.

A little tube sticking out the side of the plane is open to the air and has a pressure sensor inside it. As the pressure around the plane gets lower, the altimeter needle gets rotated to the right, showing a higher altitude. This tube is called the "static port"

You can check your plane to see if the static port is not accidentally blocked, by blowing into it. If the altimeter needle drops (high pressure is low altitude) you know it is ok and not blocked.

------------------------------------------------------------

 

The location is not what changes the pressure.

You set it to the local weather. The local air pressure.

And the weather varies from location to location.

 

Above 18.000 the altimiter should be set to 29.92. (At least, in the USA)

 

Below 18.000 it should be set to the local area (=local airport).

If you fly below 18.000 you should reset it every once in a while. I use B for that.

 

If you were so close to the ground, maybe you forgot to reset it when descending (maybe after first being above 18.000).

 

But it could also be you were flying above hills. The altitude displayed by the altimeter is "above sea level".

So, if you land at an airport in the mountains the altimeter will not show zero on the ground, but could show +1000 ft or more.

You should always check the elevation of the airport you are going to land on before making the approach. You can see it in the GPS, or in the airport data on the map.

 

------------------------------

About "above 18.000 the altimiter should be set to 29.92. (At least, in the USA)"

With all aircraft using the same altimeter setting there, you can be sure that if traffic reports being at 27.000, you are safe at 29.000 ft.

Their 27.000 is 2000 below you.

If they had a different barometer adjustment of the altimeter they could actually be at your altitude, even if their gauge showed 27.000 and yours showed 29.000.

You will notice that if you turn the barometer knob on the altimeter, your altimeter needle moves up or down.

 

Imagine at a sea level airport. Your altimeter shows 0 ft.

You could turn it so it shows 2000 ft.

The pilot in the plane next to you does not.

You both take off. He climbs to 10.000 and reports it.

You know he is on a crossing course. You climb untill your altimeter shows 12.000 and think you are safe.

But you are not. You set the altimeter earlier to indicate 2000ft too high. So you are actually at 10.000 as well.

...

 

----

I'm a lazy flyer. I don't set it manually, I just pess B regularly. I'm afraid I can't help much with your actual question "how to set it manually".;)

In fsx there are weather stations, with different barometer settings. Especially when using addon weather programs each gets it's own setting.

 

Also, pressing B will change the altimeter setting, and when that happens, the autopilot responds by climbing or descending at it's default climb /descent rate. In the b737 that is 1800 (!) ft/min. So it is wise to switch off altitude hold before pressing B and then setting a slow climb/descent rate and engaging again.

 

I have no idea how this is all done in the actual real aircraft. You would have to get the barometer settings from ATC I guess.

Because the difference between the air pressure on the ground and the air pressure around the aircraft is what makes up your altitude.

 

(Btw, I have never found out the air pressure around the aircraft in fsx. Never seen it indicated anywhere. There may be an addon gauge for it though.

It is possible to set air pressures at different altitudes in the weather setup menu in fsx.

)