I want to understand altimetry - Part 2

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Simicro
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I want to understand altimetry - Part 2

Post by Simicro »

Hi all,

Part 1 is here.

Now Part 2.

Situation 2: Simple flight from A to B with a GA AC below the US transition altitude
1. The flight is under "normal" day-to-day operations and in all the following I will use QNH
2. I am the 1st guy to fly the aicraft in the day
3. I start the engine, listen to ATIS or contact the tower, it says 30 InHg, so I set the altimeter accordingly
4. The alimeter would then display the altitude of the departure airport (possibly with a max error range of 75 ft) and that altitude would be consistent with what I can read on a aviation map
5. I take off
6. During the cruise, I need to reset the altimeter as frequently as possible by listening the ATIS of the closest station
7. Before landing I need to listen to ATIS/contact the tower of the destination airport and reset the altimeter accordingly
8. After landing, the altimeter would display the altitude of the destination airport (possibly with a max error range of 75 ft) and that altitude would be consistent with what I can read on a aviation map

Can you please tell me if what I wrote above is correct?
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DC3
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Re: I want to understand altimetry - Part 2

Post by DC3 »

Yes, it is correct.

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Simicro
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Re: I want to understand altimetry - Part 2

Post by Simicro »

Hello DC3,

Thanks for taking time to confirm me.
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Microsoft Force Feedback 2 modded with CH Fighterstick - VKB Sim T-Rudder Mk.IV Pedals

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Oracle427
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Re: I want to understand altimetry - Part 2

Post by Oracle427 »

Point 6 - It depends.

If you are using ATC drives such as flight following and flying IFR, you will get regular updates of the barometric pressure. You can expect to be tipus the pressure each time you check in after being handed off the the next controller.

Everything else sounds fine.
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Simicro
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Re: I want to understand altimetry - Part 2

Post by Simicro »

Many thanks Oracle for your confirmation, attention point and also for all your help in Part 1.

I feel I now have a good ground knowledge for "simple and normal" day-to-day flying, in a small GA AC under transition altitude.

I'm quite happy :D

I think I questioned the thing too much in the past and focused (with no reason) on maths, and that prevented me from understanding.
P3Dv4.5 - V35B - C172 - Cherokee
i5 4670K @4.3 Ghz - 32 Gb DDR3 - GTX 1080 8 Gb - 2K @165 Hz G-Sync - Win 7 x64
Microsoft Force Feedback 2 modded with CH Fighterstick - VKB Sim T-Rudder Mk.IV Pedals

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CodyValkyrie
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Re: I want to understand altimetry - Part 2

Post by CodyValkyrie »

Another cool thing you can do, is that if you know the airfield elevation (as long as it doesn’t vary much), you can figure out the barometric pressure as well. Set your altimeter to the field altitude, and BAM, there you go. I believe in the old days, it was common to check airport elevation ASL before takeoff. At many airports you can find the altitude even posted near the run up ramp or FBO (as well as being posted in appropriate charts).
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Simicro
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Re: I want to understand altimetry - Part 2

Post by Simicro »

Cool tip and info. I will try that.

Thanks CodyValkyrie!
P3Dv4.5 - V35B - C172 - Cherokee
i5 4670K @4.3 Ghz - 32 Gb DDR3 - GTX 1080 8 Gb - 2K @165 Hz G-Sync - Win 7 x64
Microsoft Force Feedback 2 modded with CH Fighterstick - VKB Sim T-Rudder Mk.IV Pedals

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