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OLC max altitude self censorship



 
 
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Old February 13th 19, 05:19 AM posted to rec.aviation.soaring
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Default OLC max altitude self censorship

I soar for fun, usually alone when normal people are working or doing some other socially responsible activity.Â* XCSoar or a (GPS-based) flywithCE position recorder is all I need for uploading .igc files to OLC.

On a warm/hot day over the Rocky Mountains, it's common to see 17,900' MSL on my barometric altimeter and 19,000' or more on any GPS height indicator I might have with me.Â* Class A airspace starts at 18,000' / FL180 / 5486m, so everything is legit, since we fly by barometric altitudes not GPS/geometric altitudes.Â* (I can get permission to fly higher, but that's not relevant to this post.)

This phenomenon of GPS altitudes exceeding barometric altitudes on warmer than "standard" (ISA) days is well explained, including in Mike Borgelt's article, "GPS Altitude vs Pressure Altitude".Â*

Before I understood this phenomenon, I thought there was something wrong with my glider's altimeter when I saw the flight's .igc (GPS only) altitude trace, which max'ed out above 19,000'.Â* Maybe I grossly busted into Class A airspace, I thought.Â* So don't upload that flight, I concluded.

Even after I understood the difference between baro vs. GPS altitudes, I found myself limiting my climbs so my.igc altitude trace shown on OLC would not raise any doubt about my maximum altitude.Â* Of course, that meant I artificially lowered my ceiling by about 1,000' on warmer days.

So my question is:Â* Has anyone using GPS-only recorders done the same -- effectively altitude "censored" yourself because of that very visible OLC altitude profile.Â* When I look at people's flights, I see lots of traces which "bounce" against that 5486m ceiling, at least over the western U..S. in the summer.Â* Sometimes, I see higher climbs with the pilot's comment that says something like, "Got ATC clearance into Class A".Â* Sometimes, I see excursions above 5486m with no comment.Â*

In other parts of the world where airpaces are different, the numbers would be different, but I imagine that kind of altitude self censorship might be happening too.

Nowadays, I generally have no problems with uploading to OLC even if my maximum GPS altitudes go above 5486m when (and because), in fact, I was legitimately (barometrically) below FL180 the whole time.Â* But I do suspect that most ATC/FAA types and even most soaring pilots would look at the altitude graph and wonder about my airspace compliance.

A related question to those who use fully IGC approved flight recorders with barometric sensors:Â* Do your .igc altitude numbers record your barometric or GPS altitudes?
 




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