OLC max altitude self censorship

[[email protected]]

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?

[kinsell]

On 2/12/19 9:19 PM, wrote:

>
> 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?
>

They record both, and you generally just look at the barometric numbers.

I feed data from a Cambridge 302 into TopHat running on a tablet, so
Tophat has access to the gps data as well as barometric altitude and
wind info.

[Roy E]

On Tuesday, February 12, 2019 at 10:19:50 PM UTC-6, wrote:
> 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*
>
>
> 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?

Yes, I have experienced the same phenomenon over mountainous terrain. My primary flight logger is an Oudie2, which is connected to a portable FLARM. The GPS altitudes are typically at least 1,000 feet higher than my altimeter, whenever I climb above about 15,000' or so. The Oudie starts bleating an airspace warning before I even reach 17,000'. This is a nuisance on great soaring days in the mountains. On those days, I sometimes stay below 17,000' just to avoid the nuisance.

I had my altimeter checked and calibrated about a year ago, so I am very confident in its accuracy, as opposed to the GPS altitude. However, without a transponder, is there any record anywhere to prove that I have NOT busted airspace floors or ceilings? If I post an OLC claim with my Oudie, where is my proof that the Oudie altitude trace is wrong? Who is going to take my word about my altimeter on any given flight?

Thankfully, I have a functioning 15-year old Colibri logger, which still works just fine. It has a piezo pressure transducer, rather than GPS altitude.. The Colibri altitude read-out typically agrees with my altimeter within about 200'. For any flight where I come close to airspace boundaries, I use the Colibri to file my OLC flight claim. A public OLC record of my flight could be used as evidence, in case anyone claims that I violated airspace.

The old Colibri loggers were very useful for a couple of us at the Cowley, Alberta 2018 summer camp. Conditions were excellent, with many high altitude and long distance XC flights. But it can be quite challenging to legally navigate all the airspace restrictions in the Cowley vicinity and north to Calgary, Alberta.

So that's my fix for this issue. Cheers!
Roy

[[email protected]]

> I had my altimeter checked and calibrated about a year ago, so I am very confident in its accuracy, as opposed to the GPS altitude. However, without a transponder, is there any record anywhere to prove that I have NOT busted airspace floors or ceilings?
>

Interesting and useful info from kinsell and Roy.Â* Thanks.

Good thought about having a transponder, if your glider has one, as a documented backup on your altitude compliance.Â* I looked up the "Flight Track Log" on FlightAware for one of my flights where I purposely limited my climb to about 17'K.Â* It showed that various ADS-B receivers pinged my ADS-B Out every 20 to 30 seconds throughout the flight, showing, among other things, my pressure altitudes.Â* Sure enough, several pings showed me topping out at 17,025'.Â* At the same time, the flywith CE log showed my max GPS altitude at 18,054'. So I could have climbed almost a thousand feet higher.

As an aside, if you have a transponder but no ADS-B Out, FlightAware would likely show you being pinged by various ATC radars (assuming you were under coverage) but at a slower ping rate, like once every minute.Â* Still useful in documenting your baro altitudes.

[Dan Daly[_2_]]

> Yes, I have experienced the same phenomenon over mountainous terrain. My primary flight logger is an Oudie2, which is connected to a portable FLARM. The GPS altitudes are typically at least 1,000 feet higher than my altimeter, whenever I climb above about 15,000' or so. The Oudie starts bleating an airspace warning before I even reach 17,000'. This is a nuisance on great soaring days in the mountains. On those days, I sometimes stay below 17,000' just to avoid the nuisance.
>
> I had my altimeter checked and calibrated about a year ago, so I am very confident in its accuracy, as opposed to the GPS altitude. However, without a transponder, is there any record anywhere to prove that I have NOT busted airspace floors or ceilings? If I post an OLC claim with my Oudie, where is my proof that the Oudie altitude trace is wrong? Who is going to take my word about my altimeter on any given flight?

> Roy

@Roy - your PowerFLARM Portable is cal'd to the ISA and that's what it records. See the approval doc at http://www.ukiws.demon.co.uk/GFAC/approvals/powerflarm.pdf
Some here: "...1.6 Pressure altitude sensor. AMS 5540 or MS 5607 Pressure Altitude sensor by MEAS Switzerland SA, formerly Intersema Sensoric SA (www.meas-spec.com) is fitted. This is compensated for temperature variation and calibrated to the ICAO ISA. It is shown in the header record of IGC files in the form: "HF PRS PressAltSensor: MEAS MS5607". The recorder case is not pressure-sealed and "cockpit static" pressure is recorded on the IGC file."

Your PowerFLARM sends pressure altitude to your Oudie2 (mine did before I changed and now my ClearNav vario does). Set up an info box with it. It will diverge from the altimeter setting on your altimeter and the GPS altitude but let you know how you are doing wrt Class A. I don't understand why your Oudie is set to alarm for GPS altitude. Oudie2 Lite running XC Soar doesn't (I assume when you say Oudie you mean SeeYou Mobile?).
Dan

[[email protected]]

Whatever your available altitude source or sources, for airspace avoidance, always fly by the one in your glider flight recorder that could be used as evidence against you.

[son_of_flubber]

If you have ADS-B out or TABS, the FAA has a record of your airspace compliance (both barometric and GPS altitudes).

https://www.faa.gov/nextgen/programs/adsb/faq/#g7

ATC's network of ADS-B receivers provides coverage in many places where radar is blocked by mountains. ADS-B Performance reports are eye-opening wrt coverage https://adsbperformance.faa.gov/paprrequest.aspx

[Dan Marotta]

The FAA and, I would guess, all other airspace control agencies, assign
altitudes according to the local altimeter setting, not GPS. Not all
aircraft are equipped with GPS (yet).Â* Above 18,000' MSL, all aircraft
set their altimeters to 29.92 in Hg (or the metric equivalent).Â*
Regardless of your GPS data points, your barometric altimeter is the
controlling instrument in flight.Â* Note that I did not bother to address
the lowest usable flight level (when atmospheric pressure is below
29.92") as I've never seen that actually used.

I've been told that the Oudie can run XCSoar should you want to do so.Â*
From my XCSoar days (and I actually still run it on the right side of
my Stemme's cockpit), I recall that, when an airspace boundary is
approached, the user is presented with a warning and buttons to ACK the
warning once (which will reset the sensing) or ACK Day (which
acknowledges the warning for the day and it won't bother you again).Â* Of
course you'll then be responsible for monitoring your own position just
like in the good old days when men were men and women were women.

My ClearNav only allows me to silence the Controlled Airspace warning
and, after pressing the "OK" button, is reset for another go.Â* That can
be annoying when a thermal is right at the side of a Restricted Area as
every time the glider's heading is towards the area, the warning goes
off again.Â* I'll have to check my manuals to see if CN has an ACK Day
ability.

Bottom line to the above long-winded story is don't worry about your GPS
track getting you into trouble on altitude so long as your altimeter is
good.Â* It's a different story with the horizontal boundaries of
controlled airspace.

On 2/14/2019 7:46 AM, son_of_flubber wrote:
> If you have ADS-B out or TABS, the FAA has a record of your airspace compliance (both barometric and GPS altitudes).
>
> https://www.faa.gov/nextgen/programs/adsb/faq/#g7
>
> ATC's network of ADS-B receivers provides coverage in many places where radar is blocked by mountains. ADS-B Performance reports are eye-opening wrt coverage https://adsbperformance.faa.gov/paprrequest.aspx

--
Dan, 5J

[Roy E]

On Thursday, February 14, 2019 at 7:01:23 AM UTC-6, Dan Daly wrote:
> >
> > I had my altimeter checked and calibrated about a year ago, so I am very confident in its accuracy, as opposed to the GPS altitude. However, without a transponder, is there any record anywhere to prove that I have NOT busted airspace floors or ceilings? If I post an OLC claim with my Oudie, where is my proof that the Oudie altitude trace is wrong? Who is going to take my word about my altimeter on any given flight?
>
> > Roy
>
> @Roy - your PowerFLARM Portable is cal'd to the ISA and that's what it records. See the approval doc at http://www.ukiws.demon.co.uk/GFAC/approvals/powerflarm.pdf
> Some here: "...1.6 Pressure altitude sensor. AMS 5540 or MS 5607 Pressure Altitude sensor by MEAS Switzerland SA, formerly Intersema Sensoric SA (www.meas-spec.com) is fitted. This is compensated for temperature variation and calibrated to the ICAO ISA. It is shown in the header record of IGC files in the form: "HF PRS PressAltSensor: MEAS MS5607". The recorder case is not pressure-sealed and "cockpit static" pressure is recorded on the IGC file."
>
> Your PowerFLARM sends pressure altitude to your Oudie2 (mine did before I changed and now my ClearNav vario does). Set up an info box with it. It will diverge from the altimeter setting on your altimeter and the GPS altitude but let you know how you are doing wrt Class A. I don't understand why your Oudie is set to alarm for GPS altitude. Oudie2 Lite running XC Soar doesn't (I assume when you say Oudie you mean SeeYou Mobile?).
> Dan

Dan,
Yes my Oudie2 runs on SeeYou. I bought it about 5 years ago and connected it to the portable FLARM with the Oudie2 cables. My Oudie2 altitude trace, as filed on OLC, has always shown the GPS altitude. That was one reason why I had my altimeter re-calibrated ($500). Perhaps there's a setting or "switch" for the pressure altitude output, which I'm supposed to configure in the FLARM and/or the Oudie2??
I'll have to check that out in the glider, if and when spring ever arrives.

Also: Other users claim that their Oudie shows flarm targets on the Oudie display. Mine has never done that. I asked Dave Springford about that a few years ago, and he sent me a copy of the configuration file to make that work. But mine was already set that way. So I'm lost.

Thanks!
Roy

[mic pilot]

On Tuesday, February 12, 2019 at 10:19:50 PM UTC-6, wrote:
> 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?

Just make sure to update the setting in your baro window to what ATC is issuing other traffic. The rule is use a setting with in 100nm. The only time you would be too high (ie in class A) is if your setting was say 29.82 and the actual was 29.92. That case you would be 100 feet higher than your altimeter and 17,900 would be in class A.

[[email protected]]

> Just make sure to update the setting in your baro window to what ATC is issuing other traffic. The rule is use a setting with in 100nm. The only time you would be too high (ie in class A) is if your setting was say 29.82 and the actual was 29.92. That case you would be 100 feet higher than your altimeter and 17,900 would be in class A.

Unless I'm in taking off or landing, my radio is usually on frequency scan mode to listen to several tower/approach/center frequencies, so having the appropraite altimeter setting is never a problem.Â* But it's a good point to make about checking and dialing it in.

[kirk.stant]

> Dan,
> Yes my Oudie2 runs on SeeYou. I bought it about 5 years ago and connected it to the portable FLARM with the Oudie2 cables. My Oudie2 altitude trace, as filed on OLC, has always shown the GPS altitude. That was one reason why I had my altimeter re-calibrated ($500). Perhaps there's a setting or "switch" for the pressure altitude output, which I'm supposed to configure in the FLARM and/or the Oudie2??
> I'll have to check that out in the glider, if and when spring ever arrives.
>
> Also: Other users claim that their Oudie shows flarm targets on the Oudie display. Mine has never done that. I asked Dave Springford about that a few years ago, and he sent me a copy of the configuration file to make that work. But mine was already set that way. So I'm lost.
>
> Thanks!
> Roy

Roy,

I would bet your PF is not sending any data to your Oudie; which would explain your indications - the log file is using the Oudie's GPS to make the trace. I don't have my Oudie with me right now, but there is a page you can check to see what data is coming in to it; I would look there. If all works correctly, you will get pressure alt and Flarm/ADS-B/PCAS targets on your Oudie display.

Kirk
66

[Dan Marotta]

Just to add to that, with XCSoar, on the page which controls the
interfaces (Config -> Devices), when you select one of the interfaces,
i.e., Flarm, there's a Monitor button which, when pushed, displays the
message traffic in real time.Â* There are also similar buttons for the
ClearNav interface/data stream.Â* Maybe there's something similar with
the Oudie/SeeYou?

On 2/28/2019 1:47 PM, kirk.stant wrote:
>> Dan,
>> Yes my Oudie2 runs on SeeYou. I bought it about 5 years ago and connected it to the portable FLARM with the Oudie2 cables. My Oudie2 altitude trace, as filed on OLC, has always shown the GPS altitude. That was one reason why I had my altimeter re-calibrated ($500). Perhaps there's a setting or "switch" for the pressure altitude output, which I'm supposed to configure in the FLARM and/or the Oudie2??
>> I'll have to check that out in the glider, if and when spring ever arrives.
>>
>> Also: Other users claim that their Oudie shows flarm targets on the Oudie display. Mine has never done that. I asked Dave Springford about that a few years ago, and he sent me a copy of the configuration file to make that work. But mine was already set that way. So I'm lost.
>>
>> Thanks!
>> Roy
> Roy,
>
> I would bet your PF is not sending any data to your Oudie; which would explain your indications - the log file is using the Oudie's GPS to make the trace. I don't have my Oudie with me right now, but there is a page you can check to see what data is coming in to it; I would look there. If all works correctly, you will get pressure alt and Flarm/ADS-B/PCAS targets on your Oudie display.
>
> Kirk
> 66
>

--
Dan, 5J

[Roy E]

On Thursday, February 28, 2019 at 2:47:54 PM UTC-6, kirk.stant wrote:

> Roy,
>
> I would bet your PF is not sending any data to your Oudie; which would explain your indications - the log file is using the Oudie's GPS to make the trace. I don't have my Oudie with me right now, but there is a page you can check to see what data is coming in to it; I would look there. If all works correctly, you will get pressure alt and Flarm/ADS-B/PCAS targets on your Oudie display.
>
> Kirk
> 66

Thanks Kirk,
That was indeed the root cause. Dave Springford guided me through the proper settings on the Oudie. After selecting the proper settings, the Oudie reads the pressure altitude and the Flarm display is visible on the Oudie. This is with the glider sitting indoors. I'm very hopeful that the targets will show in flight!
Thanks again,
Roy