Watching C17 nearby and noticed a big split between Baro and Geo altitude. Maybe Ive never looked close but it doesnt seem right
Altitude (Barometric):
33,975 ft
Altitude (Geometric):
35,000 ft
Check other planes at similar altitude.
Then you know what’s up.
just all my years of flying never saw a density/pressure alt so much different than Geo.
But thanks.
The difference will be bigger at higher altitudes.
But i’ll assume you’ve flown up at FL350 
If you aren’t referring to the flight levels, you used the altimeter setting to correct the altitude displayed in the plane.
The baro alt sent via 1090 MHz is always uncorrected, ATC applies the correction based on local altimeter.
But ADS-B decoders don’t know the local altimeter so it’s best to just display it uncorrected.
I have, I was a Naval Aircrewman. But, this was in the 70s and 80s. So we didnt have all the fancy stuff we have now. Most advanced Nav System was the Litton 51. Altimiters were set to 29.92 at 10K and we drove on.
But I see that ADSB doesnt so yes big split. Looking at other aircraft around I see up to 1K, but not that big of a split.
Good thing they standardized all the settings a way back when or collosions would be worse :).
Yeah that’s what is broadcast by the transponder, as if the altimeter was set to 29.92.
I don’t know how rare the 1000 ft split is, i don’t check regularly.
800 ft to day for the first plane i checked in the US.
1200 ft at FL410 over central Europe.
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