What does calibrated altitude equal to in MSL?

[GsquaredAerials]

So this Life-star helicopter flew right over my neighborhood this evening and I swear he was near 400 AGL max. I wasn't flying but I would have shipped my pants (Kmart commercial reference) if I was. I'm sure he has ADS-B but I just made a post this weekend about not getting ADS-B warnings on my radio form a Cessna flying over but at a much higher altitude. Anyway, I played back the Life-star flight and it says he was at 1650 calibrated altitude right over my house. Figuring that's MSL, I deducted 900ft from my home's MSL and got 750ft. Ain't no way he was 750ft AGL. Is my math wrong or am I leaving out some adjustment the pilot sets for barometric pressure?

Google says "Calibrated altitude is corrected for nonstandard atmospheric conditions. It is the actual height above mean sea level, as if measured with a tape measure. Elevations of airports, mountaintops, towers and other obstructions are given in true altitude".

I know sometimes looks can be deceiving when looking at objects in the distance or in this case in the air but I'm telling you, I'm pretty sure I know the difference between 400ish feet and 750ft. Just ranting. No point to this post.

 

[R.Perry]

So this Life-star helicopter flew right over my neighborhood this evening and I swear he was near 400 AGL max. I wasn't flying but I would have shipped my pants (Kmart commercial reference) if I was. I'm sure he has ADS-B but I just made a post this weekend about not getting ADS-B warnings on my radio form a Cessna flying over but at a much higher altitude. Anyway, I played back the Life-star flight and it says he was at 1650 calibrated altitude right over my house. Figuring that's MSL, I deducted 900ft from my home's MSL and got 750ft. Ain't no way he was 750ft AGL. Is my math wrong or am I leaving out some adjustment the pilot sets for barometric pressure?

Google says "Calibrated altitude is corrected for nonstandard atmospheric conditions. It is the actual height above mean sea level, as if measured with a tape measure. Elevations of airports, mountaintops, towers and other obstructions are given in true altitude".

I know sometimes looks can be deceiving when looking at objects in the distance or in this case in the air but I'm telling you, I'm pretty sure I know the difference between 400ish feet and 750ft. Just ranting. No point to this post.

View attachment 4142

750 feet, I would get lost at the altitude, I couldn't read the street signs. I was once a crop duster. In reality, judging the altitude of another aircraft can be tough because of the variations in the size of different aircraft. Helicopter pilots are a different breed and flying low is a norm for them. Main thing is we just need to stay out of their way.

 

[R.Perry]

Oh, by the way, when the barometric pressure changes pilots must reset their altimeters to the current pressure. This is critically important for pilots flying in IFR (that doesn't mean I FOLLOW ROADS ) conditions and severe weather where the pressure can change rapidly.

 

[GsquaredAerials]

Yeah I learned about that in the Pilot Institute training.

 

[BigAl07]

Barometric Pressure - As it changes the altimeter reading changes. So when you get the pressure at your landing/takeoff location you adjust your altimeter to reflect that change so that your altitude is more accurate for the area you're in.

It's VERY hard for the normal person to accurately judge an aircraft's altitude. It takes training and practice to even get remotely close and it requires some type of "reference" so you can compare the aircraft to it. Just looking at an aircraft you're going to get it wrong 99 out of 100 times. The larger the aircraft the less accurate you are.

 

[GsquaredAerials]

Barometric Pressure - As it changes the altimeter reading changes. So when you get the pressure at your landing/takeoff location you adjust your altimeter to reflect that change so that your altitude is more accurate for the area you're in.

It's VERY hard for the normal person to accurately judge an aircraft's altitude. It takes training and practice to even get remotely close and it requires some type of "reference" so you can compare the aircraft to it. Just looking at an aircraft you're going to get it wrong 99 out of 100 times. The larger the aircraft the less accurate you are.

Wow! Kind of reminds me of a bet I lost once about how far the other side of a large river was. I said for sure, no more than 300 yards across. It was more than double.

 

[Airmapper]

It says GPS altitude on that screenshot you posted. That is not impacted by pressure changes.

 

[GsquaredAerials]

No, the GPS altitude is a locked feature underneath.

 

[Airmapper]

No, the GPS altitude is a locked feature underneath.

Ok I see. You can probably look up the tail number on ADSBexchange, should not be a restricted feature on there. Go in the history field on the left hand panel, navigate to the date it flew and you should be able to pick a node at the desired location and get all the details. Will probably be labeled WGS84 Altitude.

Here is a link, you'll have to narrow down the location and time.

ADS-B Exchange - track aircraft live

ADS-B Exchange - track aircraft live - aircraft flight history

globe.adsbexchange.com

 

[GsquaredAerials]

Thanks for the link. I actually use ADS-B Exchange to follow military aircraft. Alright so my eyeballs were slightly off. My house is 338m MSL (1108ft) so 1675 - 1108 = 567ft. Again, that states barometric altitude so I guess I'd have to know the pressure that day at the airport he took off from and I'm good to just stop here