Garmin 496 altitude 450 feet off

Bubblehead · #1 07-12-2011, 02:56 PM

I've been flying with my Garmin 496 for almost 4 years now and the altitude readout on the instruments page always shows me about 450 feet higher than my altimeter says. I really did not pay any attention to that until a couple of months ago.

Is there a way to correct that? Anyone know why that is?

n5lp · #2 07-12-2011, 03:21 PM

Quote:

Originally Posted by Bubblehead

I've been flying with my Garmin 496 for almost 4 years now and the altitude readout on the instruments page always shows me about 450 feet higher than my altimeter says. I really did not pay any attention to that until a couple of months ago.

Is there a way to correct that? Anyone know why that is?

How does the 496 altitude display compare to a known ground elevation when you are just sitting still?

Walt · #3 07-12-2011, 03:25 PM

GPS and pressure altitude are two different things, sit back relax and read all about it HERE

gasman · #4 07-12-2011, 06:43 PM

I have a 2000C and I get upset when it gets more than 50 feet off.
And it never gets more than 100 feet off.

LifeofReiley · #5 07-12-2011, 06:49 PM

Quote:

Originally Posted by gasman

I have a 2000C and I get upset when it gets more than 50 feet off.
And it never gets more than 100 feet off.

Pretty much the same here and it sure won't be a constant... 450 ft off all the time, something has to be wrong somewhere.

Wayne Gillispie · #6 07-12-2011, 07:33 PM

is always within 50' of altimeter too as I recall.

L.Adamson · #7 07-12-2011, 07:54 PM

Quote:

Originally Posted by gasman

I have a 2000C and I get upset when it gets more than 50 feet off.
And it never gets more than 100 feet off.

Then you don't fly to enough places...

When I reset my altimeter to a current pressure setting, the "six pac" page of my Garmin 696 & aircraft's alimeter will often read nearly exactly the same. The dials will just follow each other. This might last 10 mins or so..........considering there is variations with barametric pressure.

And once I've moved a bit on the ramp, the 696 also nails the airport altitude within feet. But I have seen variations of 200+ feet between the two, while in flight. If anything, the GPS is showing a more accurate altitude in regards to terrain. The altimeter is showing an altitude needed for ATC and seperation.

L.Adamson --- RV6A

Frank Smidler · #8 07-12-2011, 07:57 PM

I also noted the same issue with my Garmin 296. The other day it was very hot and at an altitude of 4500 ft the GPS showed a higher altitude by 270 to 300 ft. On the ground they both showed the correct altitude.

etekberg · #9 07-15-2011, 01:54 PM

Your altimeter lies to you. It does not correct for temperature and it only is accurate when you are very close in altitude to the report station (the airport). The higher you are the farther it is off. When it is hotter than standard it reports lower than you actually are (a safe condition). When it is colder than standard it report higher than you actually are (a dangerous condition). That is why you will see notes on instrument charts that say Baro VNAV N/A below XX degrees.

GPS altitude is more correct, especially WAAS enhanced GPS.

Kevin Horton · #10 07-15-2011, 04:29 PM

Quote:

Originally Posted by etekberg

GPS altitude is more correct, especially WAAS enhanced GPS.

But the definition of "correct" depends on exactly what you are trying to do. If you are trying to measure the elevation of mountain top, GPS is almost certainly more correct than the barometric altimeter out of your aircraft. But, if you are trying to follow ATC's instruction to fly at 6000 ft, the barometric altimeter on your instrument panel will be much, much more correct than the GPS. Given that this forum is about aircraft in today's ATC environment, the barometric altimeter is the correct reference as everything is based on barometric altitudes.