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A comment on WiFi without internet on a Southwest flight. Parent comment

Re:WiFi without internet on a Southwest flight by chatmasta on Thursday September 28, 2023 @02:20PM (#37693532)
The plane is measuring altitude, which is relative to a reference point, unlike elevation which is relative to sea level. And if the altitude is determined by pressure sensor, musn't it be relative to the ground directly below the plane, anyway?

(Although personally, I agree with the sibling comment that the variability is likely an artifact of the sensor resolution.)

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Re:WiFi without internet on a Southwest flight by adastra22 on Thursday September 28, 2023 @02:44PM (#37693869)
Planes dont measure height relative to the ground. How would that even work? Their sensor is air pressure, which is treated as a function of elevation.
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Re:WiFi without internet on a Southwest flight by jjwiseman on Thursday September 28, 2023 @02:49PM (#37693935)
They do sometimes! Via radar altimeters, when relatively close to the ground. And sometimes to keep autopilots from freaking out, we have to build radar reflectors to make the ground look level to radar even when it's really not. https://lustublog.com/2017/02/17/artificiel-mais-pas-superfi...
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Re:WiFi without internet on a Southwest flight by jjwiseman on Thursday September 28, 2023 @02:44PM (#37693873)
When you climb to the top of Mt. Everest, the air pressure is about 1/3 of what it is at sea level even though you're standing on the ground.
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Re:WiFi without internet on a Southwest flight by chatmasta on Thursday September 28, 2023 @04:58PM (#37695743)
Yeah, you make a very good point. Fortunately the blast radius of my scientific hubris is limited to whatever code I manage to deploy to the internet, and I'm not involved in designing or building aircraft.

btw: Aren't you the guy who tracks planes flying in circles? I follow you on Twitter. Such a cool project!

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Re:WiFi without internet on a Southwest flight by victortroz on Thursday September 28, 2023 @03:01PM (#37694091)
It's relative to sea level. After transition altitude (18k feet in most places) the pressure setting to the altimeter is changed to standard (iirc 1013 hPa) so all aircrafts are in the same reference regardless of terrain.
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Re:WiFi without internet on a Southwest flight by epse on Thursday September 28, 2023 @04:11PM (#37695134)
Most places in the US, but accurate
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