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Altimeter Setting vs Field Elevation

Vflyer

Well-Known Member
#1
The last couple of flights I've had I noticed the altimeter did not match the field elevation when inputting the current baro pressure from ATIS. In fact it was off by 150-200ft. I'm embarrassed to admit I can't figure out why. I was trying to equate it to temperature, but it would seem the pressure at a given level, is the pressure regardlesss of temp.

The field is basically at sea level (10ft) yet the altimeter typically indicates 200ft below this. It makes me wonder if I should be accounting for this "error" or assume the altimeter setting is correct and fly at assigned altitudes regardless.

I did some googling to no avail so hopefully this question isn't too dumb!
 

Cessnaflyer

Wooooooooooooooooooooooooooooooo
#5
The last couple of flights I've had I noticed the altimeter did not match the field elevation when inputting the current baro pressure from ATIS. In fact it was off by 150-200ft. I'm embarrassed to admit I can't figure out why. I was trying to equate it to temperature, but it would seem the pressure at a given level, is the pressure regardlesss of temp.

The field is basically at sea level (10ft) yet the altimeter typically indicates 200ft below this. It makes me wonder if I should be accounting for this "error" or assume the altimeter setting is correct and fly at assigned altitudes regardless.

I did some googling to no avail so hopefully this question isn't too dumb!
Temperatures do have affect reading but I doubt it was cold enough at sea level to be reading 200 feet lower unless you were in the polar regions.
 

Vflyer

Well-Known Member
#6
Thanks that's good to know. The plane is a rental so best I can do is squawk it for now. I don't think it gets used much for ifr so there probably won't be much motivation to fix it.
 
#7
Thanks that's good to know. The plane is a rental so best I can do is squawk it for now. I don't think it gets used much for ifr so there probably won't be much motivation to fix it.
I would consider 200' to be a safety of flight issue. If it is a rental, vote with your feet. Don't fly it until it is fixed or replaced (more likely). They aren't that expensive...
 

Roger Roger

Paid to sleep, fly for fun
#8
I would consider 200' to be a safety of flight issue. If it is a rental, vote with your feet. Don't fly it until it is fixed or replaced (more likely). They aren't that expensive...
This is why I started doing altimeter certs even on our VFR only planes.
 
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Roger Roger

Paid to sleep, fly for fun
#9
They aren't that expensive...
About 12 airplane bucks for the ones we use. Might could get it repaired but typically the shop says that by the time they're that far out it's cheaper to buy a new one than to replace, depending on the age and type of altimeter. Of course a real operation should have a current cert altimeter on hand that they could swap in and not have an AOG but...
 
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BaronPete

Jaw Harp Troubadour
#12
So an altimeter replacement is about 1200$ ?

I realize everything is expensive, but I wouldn't have guessed that. I figured 400-500 tops.

But then again, I'm dumb.
 

flyboy6585

Well-Known Member
#14
Just make sure you are comparing it to known elevation points. Just because the airfield elevation is 10' doesn't mean there aren't places that differ significantly. Quite possible not the issue here, just worth bringing up.