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Flat Earth General / Re: Why do airplanes fly at the height they fly at?
« on: January 24, 2021, 04:20:25 AM »
@jack44556677
In aviation there are strict definitions for the terms "height", "altitude", and "pressure altitude" (referenced to "standard" 1013.2 hpa). Do a bit of googling!! A pressure change of 1 hpa (mb) equates to approx 30ft. Also google "altimeter temperature errors" and "international standard atmosphere (isa)". If the air beneath the aircraft is colder than standard, the aircraft will be lower than indicated (and vice versa). A barometric altimeter is effectively measuring the weight of air beneath the aircraft to derive a reading.
As I'm sure Gonzo will confirm, on really really cold days aircraft on approach will be vectored in at higher platform altitudes to maintain ground and obstacle clearance. Altimeter error is approx 4% for every 10 degrees above or below isa. If it's cold, the air beneath the aircraft is denser. If flying a non-precision approach (more google research for you) on cold days we make corrections to the final approach altitude profile to adjust for this error.
Barometric altimeters are very accurate, you just have to know what they are measuring!
@Gonzo
I guess we've spoken to each other many times!!
In aviation there are strict definitions for the terms "height", "altitude", and "pressure altitude" (referenced to "standard" 1013.2 hpa). Do a bit of googling!! A pressure change of 1 hpa (mb) equates to approx 30ft. Also google "altimeter temperature errors" and "international standard atmosphere (isa)". If the air beneath the aircraft is colder than standard, the aircraft will be lower than indicated (and vice versa). A barometric altimeter is effectively measuring the weight of air beneath the aircraft to derive a reading.
As I'm sure Gonzo will confirm, on really really cold days aircraft on approach will be vectored in at higher platform altitudes to maintain ground and obstacle clearance. Altimeter error is approx 4% for every 10 degrees above or below isa. If it's cold, the air beneath the aircraft is denser. If flying a non-precision approach (more google research for you) on cold days we make corrections to the final approach altitude profile to adjust for this error.
Barometric altimeters are very accurate, you just have to know what they are measuring!
@Gonzo
I guess we've spoken to each other many times!!