Inogen

[dkkim73]

Some construct based models with a few parameters would a good start. Fun project to work on ....

[N201MKTurbo]

9 hours ago, dkkim73 said:

And I thought actual science was dead in the centralized funding + corporate media era. 

Great thread. 

This is an area begging for some inexpensive NORSEE safety equipment. 

I think the guy who mentioned capnography has some ideas...

For effective breathing, we need to inhale through out noses and exhale through out mouths. That would require a CO2 sensor in your mouth. Perhaps it could be built into your headset microphone.

[Marc_B]

I reached out to FAA Civil Aerospace Medical Institute (CAMI) and they're looking to see if any recent studies have been performed with modern oxygen concentrators.  They sent me a prior study using molecular sieve oxygen concentrators, and the AC on portable oxygen concentrator use in flight (more geared to pax bringing concentrator than pilot use).

From their comments:

*  Generally, 1.5 Liter per min flow rate is only good up to 15,000 feet. 2.0 liter flow is good up to 20,000 feet. You see the connection. 2.5 liters would be required at 25,000 and 2.8 at 28,000. Obviously if you’re over 25,000 feet you would be in a pressurized aircraft (by FAR). And if these are molecular sieves that concentrate the oxygen there is typically an argon build up int stored oxygen (some units are high as 5%. That would account for the variability of the oxygen % levels. But that was with older models…newer ones may be better at scrubbing the argon out.

*  Questions about the practicality (and regulation) of using portable oxygen (O2) concentrators designed for medical use in general aviation (GA) aircraft have come up a lot lately.  It’s questionable as to whether these units can remain efficient in an unpressurized cabin at higher altitudes (~ 10,000 up to 25,000 feet), even with a cranked up O2 flow rate.  CAMI tested some portable O2 concentrators in an altitude chamber up to 30,000 feet back in the early 1990s (1st attachment),  but this research was with very early model concentrators, which I suspect have vastly improved since then. CAMI has conducted no further/recent research on such units. We’re doing a trawl of the research/medical/aviation literature to see if there’s anything more recent; I’ll let you know if we come up with anything.

 

The general gist is that there was WIDE variety of altitude limits show with the study done in 1992 from equipment to equipment (see page 6, figure 2).  Modern oxygen concentrators MAY, or MAY NOT, have better efficiency and efficacy with oxygen concentration.  The big question is what is the composition of concentrator output at high altitude?  Given that the density of air at high altitude is less, the total amount of oxygen in the air is low even if it's much higher concentration proportionally.  So in many respects, what we have to base use on is manufacturing data (not sure the details of what was tested and how in many cases), and field trials.  But we do have the use of pulse oximeters that can help guide individual use to say that at minimum if equipment is, or is not, able to provide basic SPO2 requirements.

Regardless of the equipment you use, I'd recommend that every pilot use a pulse oximeter regularly and test flight performance of their equipment on routine basis to make sure that the cannula, mask, flow rate, pulse dose, etc. work with their physiology and flight profile.

Portable Oxygen Concentrators (AC_120-95A; 24 MAY 2016)-1.pdf Comparisons of Molecular Sieve O2 Concentrators for Potential Medical Use Aboard Commercial ACFT (England et al., 1992)_DOT-FAA-AM-92_22-1.pdf

[201Mooniac]

2 minutes ago, Marc_B said:

Obviously if you’re over 25,000 feet you would be in a pressurized aircraft (by FAR). 

Unless you are in a 252 :-), certified to 28,000ft, I've never flown one above 25,000 though and that only once and with another pilot on a separate O2 source, maybe I'm chicken but 25,000 is a little too high for me to feel comfortable alone given how rapidly hypoxia can set in with an O2 failure.

[Jeff Uphoff]

58 minutes ago, 201Mooniac said:

Unless you are in a 252 :-), certified to 28,000ft, I've never flown one above 25,000 though and that only once and with another pilot on a separate O2 source, maybe I'm chicken but 25,000 is a little too high for me to feel comfortable alone given how rapidly hypoxia can set in with an O2 failure.

Did the follow-on M20K incarnation, the Encore, also carry the 252's FL280 ceiling?

(I rarely took my 231 above 17k'--a few times to FL190 and I think once to FL210; I didn't care much for my chances in the event of an O2 failure up there, either.)

--Up.

[201Mooniac]

28 minutes ago, Jeff Uphoff said:

Did the follow-on M20K incarnation, the Encore, also carry the 252's FL280 ceiling?

I don't know, I never flew one.  I flew a 252 with Chris W. from CA to NY and we took that one as high as FL250 but no higher.

[Marc_B]

I was always curious about the change to the Encore that made Mooney decide to show the operating altitude of the 252 as FL280 vs FL250 for the Encore.  But it's certainly in the POH.  Does anyone know the background history for this??

 

From POH 3303 revA for the M20K Encore:

 

But for the M20K 252 Information manual Number 0033550, Date 3-90:

[Jeff Uphoff]

1 minute ago, 201Mooniac said:

I don't know, I never flew one.  I flew a 252 with Chris W. from CA to NY and we took that one as high as FL250 but no higher.

Was that Vince's? When y'all flew it east for him and then a bunch of us wound up on Tangier Island?

--Up.

[201Mooniac]

18 minutes ago, Jeff Uphoff said:

Was that Vince's? When y'all flew it east for him and then a bunch of us wound up on Tangier Island?

Yep, that's the one.

[Paul Thomas]

1 hour ago, Marc_B said:

I was always curious about the change to the Encore that made Mooney decide to show the operating altitude of the 252 as FL280 vs FL250 for the Encore.  But it's certainly in the POH.  Does anyone know the background history for this??

 

From POH 3303 revA for the M20K Encore:

 

But for the M20K 252 Information manual Number 0033550, Date 3-90:

I have read that the test pilots took it to 28,000 in testing to achieve the numbers set by the marketing department.

[Fly Boomer]

2 hours ago, Marc_B said:

I was always curious about the change to the Encore that made Mooney decide to show the operating altitude of the 252 as FL280 vs FL250 for the Encore.

It's my understanding, although I can't cite a reference, that the FAA paperwork for 28,000 dwarfs the paperwork for 25,000.  Mooney probably lost their appetite for having the highest flying light airplane around.

[MikeOH]

38 minutes ago, Fly Boomer said:

It's my understanding, although I can't cite a reference, that the FAA paperwork for 28,000 dwarfs the paperwork for 25,000.  Mooney probably lost their appetite for having the highest flying light airplane around.

Related, but TOTAL thread drift.

Close to 200 people have CLIMBED Mt. Everest (29,000 feet) WITHOUT oxygen!!  I find that little fact INSANE!

[donkaye, MCFI]

3 minutes ago, MikeOH said:

Related, but TOTAL thread drift.

Close to 200 people have CLIMBED Mt. Everest (29,000 feet) WITHOUT oxygen!!  I find that little fact INSANE!

Being Hypoxic, they probably didn't know what they were doing.

[N201MKTurbo]

322 people have died climbing  Mt Everest mostly from Acute Mountain Sickness (hypoxia)

[Pinecone]

12 hours ago, Jeff Uphoff said:

Did the follow-on M20K incarnation, the Encore, also carry the 252's FL280 ceiling?

No, the Encore is 25K.  And if you convert a 252 to Encore, you inherit the Encore POH, so lower max altitude.

[Pinecone]

10 hours ago, Paul Thomas said:

I have read that the test pilots took it to 28,000 in testing to achieve the numbers set by the marketing department.

And Bob Kromer said that once was enough, he never wanted to do that again.

 

[Pinecone]

14 hours ago, Marc_B said:

*  Generally, 1.5 Liter per min flow rate is only good up to 15,000 feet. 2.0 liter flow is good up to 20,000 feet. You see the connection. 2.5 liters would be required at 25,000 and 2.8 at 28,000. Obviously if you’re over 25,000 feet you would be in a pressurized aircraft (by FAR). And if these are molecular sieves that concentrate the oxygen there is typically an argon build up int stored oxygen (some units are high as 5%. That would account for the variability of the oxygen % levels. But that was with older models…newer ones may be better at scrubbing the argon out

Interesting.  The Inogen One G5 specs I found says it delivers a max of 1.26 liters per minute.  So you would only be good to 12,600 according to that data.

But we know that it works for many people, including me, at 17,000 for one person and 14,000 for two people.  But it, like the Mountain High O2D2 delivers a pulse of O2 on inhalation, so all the oxygen delivered goes into the lungs versus a continuous flow system that is blowing O2 even while you exhale.

I just looked up the manual for the O2D2 and the section on oxygen duration.  From their table, it looks like it delivers about 0.272 LPM at 10,000 feet, 0.562 LPM at 15,000, and about 0.722 LPM at 18,000.

Based on those numbers and the pulse delivery, 14,000 for two on an Inogen is reasonable and for a single person it should be good to over 18,000.  With 2 people on an Inogen, it is wasting some oxygen as one person inhales and the other person is not, it delivers to both cannulas.

Here is an AOPA article that also points to 1 LPM per 10,000 feet

https://www.aopa.org/news-and-media/all-news/1998/september/pilot/o2-issues

And an FAA report on portable O2 systems, but I have not had time to really read it yet, so don't know if it talks about flow rates.

https://www.faa.gov/sites/faa.gov/files/data_research/research/med_humanfacs/oamtechreports/AM98-27.pdf

[Jeff Uphoff]

50 minutes ago, Pinecone said:

And Bob Kromer said that once was enough, he never wanted to do that again.

 

I remember him posting some to the old Mooney email lists about the 252 flight testing....

--Up.

[Marc_B]

On 7/8/2025 at 6:01 AM, Pinecone said:

Based on those numbers and the pulse delivery, 14,000 for two on an Inogen is reasonable and for a single person it should be good to over 18,000.  With 2 people on an Inogen, it is wasting some oxygen as one person inhales and the other person is not, it delivers to both cannulas.

I think this is a little more nuanced than just flow rate. The 1LPM per every 10,000 feet is a rough rule of thumb and based on aviation grade oxygen equipment.

There is a difference in the composition of the output from a bottle of oxygen and an oxygen concentrator (potentially dramatically at altitude). I.e. aviation grade as well as medical grade is 99.5% (or better) pure oxygen. But oxygen concentrators may not be able to provide that above a certain altitude as the partial pressure of oxygen is much lower than sea level. 
 

From the study I linked above from CAMI, some of the concentrators they tested reached a certain altitude and dropped the oxygen output quite a bit. Sounds like some of them also started to rise in levels of other noble gases like argon. BTW, argon is inert and non toxic but can displace oxygen in a "confined space" because it is more dense than oxygen  

 

This discussion isn’t one of “you can’t do this” or “you shouldn’t do that”. It’s a nuanced discussion of the actual limited data we have pertaining to oxygen concentrators. They aren’t all the same and may not all perform the same at altitude. We need more data to replace the speculation. 

[kortopates]

1 hour ago, Pinecone said:

And Bob Kromer said that once was enough, he never wanted to do that again.

 

It certainly wasn't just factory test pilots that flew it high. There was at least one 252 owner I knew of that flew his 252 at 28K as often as he could for the added speed.

FL280 certification testing was done on on the 252 only be able to claim 252 mph cruise. Of course they would have been happier if they got that at 25K but it fell short.

After that the goal of Encore was fixing the limited useful load issue in all the K's since it kept going lower with all the standard options. Nobody really cared about ceiling limits, just preserving speed and adding useful load. 

[MikeOH]

4 hours ago, Marc_B said:

This discussion isn’t one of “you can’t do this” or “you shouldn’t do that”. It’s a nuanced discussion of the actual limited data we have pertaining to oxygen concentrators. They aren’t all the same and may not all perform the same at altitude. We need more data to replace the speculation. 

Exactly!

The question I have is, if your O2 monitor shows good SpO2 does it matter where the O2 is coming from?  I.e., doesn't that render all of these O2 concentration, Ar dilution, etc. issues moot?

[Marc_B]

I would think that a normal SPO2 if it correlates should confirm that oxygen equipment is working as intended in the absence of CO poisoning which could result in falsely elevated SPO2. 
 

However the previous general “rules of thumb” that may have applied with other equipment doesn’t necessarily apply to different equipment with potentially different outputs.

The big “catch 22” is that oxygen concentrators may have a service ceiling that affects output concentrations, whereas a bottle of aviator grade oxygen is 99.5% + oxygen regardless of altitude.

So when you factor in pulse delivery vs constant flow, variability in oxygen concentration, and unknown service ceiling…you have to realize that you’re potentially a test pilot and should test yourself and occupants as well as monitor your SPO2 accordingly.

You can’t use the flow rate of on board oxygen as synonymous to a concentrator at altitude. It’s not the same thing. Of course when I’m flying at altitude I’m “titrating to effect” based on pulse ox, as I’m sure we all do these days.

It wasn’t that long ago that we didn’t have ubiquitous and accurate ways to monitor oxygen saturation real time and flew based on “rules of thumb”. 

[Pinecone]

22 hours ago, Marc_B said:

I think this is a little more nuanced than just flow rate. The 1LPM per every 10,000 feet is a rough rule of thumb and based on aviation grade oxygen equipment.

There is a difference in the composition of the output from a bottle of oxygen and an oxygen concentrator (potentially dramatically at altitude). I.e. aviation grade as well as medical grade is 99.5% (or better) pure oxygen. But oxygen concentrators may not be able to provide that above a certain altitude as the partial pressure of oxygen is much lower than sea level. 
 

From the study I linked above from CAMI, some of the concentrators they tested reached a certain altitude and dropped the oxygen output quite a bit. Sounds like some of them also started to rise in levels of other noble gases like argon. BTW, argon is inert and non toxic but can displace oxygen in a confined space (ie mask) because it is more dense than oxygen  

This discussion isn’t one of “you can’t do this” or “you shouldn’t do that”. It’s a nuanced discussion of the actual limited data we have pertaining to oxygen concentrators. They aren’t all the same and may not all perform the same at altitude. We need more data to replace the speculation. 

The point was that the manufacturer recommendations and the experience of those using an Inogen seem to match to the delivery from the Mountain High O2D2.   Just another data point.

FYI there is NO WAY for argon to concentrate in a mask.  The turbulence in the mask will keep all the gases mixed in that small volume.  

If what you say was true, it would be easy to separate out the various gases by letting a container sit the removing one layer at a time.

[Aaviationist]

10 minutes ago, Pinecone said:

The point was that the manufacturer recommendations and the experience of those using an Inogen seem to match to the delivery from the Mountain High O2D2.   Just another data point.

FYI there is NO WAY for argon to concentrate in a mask.  The turbulence in the mask will keep all the gases mixed in that small volume.  

If what you say was true, it would be easy to separate out the various gases by letting a container sit the removing one layer at a time.

I don’t believe we have seen a direct comparison as a real world test in this thread. 
 

what we do have is someone that went well into the flight levels, with 2 people, without a mask, and advertised they were still at 90% (or something like that)

those are not good numbers and that IS hypoxic. 
 

we also know that the most popular sensors tend to be inaccurate at concentrations below 95% so we don’t REALLY know in this example. 

[wombat]

On 7/8/2025 at 11:07 AM, MikeOH said:

Exactly!

The question I have is, if your O2 monitor shows good SpO2 does it matter where the O2 is coming from?  I.e., doesn't that render all of these O2 concentration, Ar dilution, etc. issues moot?

In some cases, I think it does.   For example, I think you are prohibited from using a nasal cannula above 18,000' MSL, if that device has been certified for aviation use and has a prohibition against use above 18,000'.  This is because the FAA has made the manufacturers prohibit it in order to be certified.   The way I see it, that's no different than exceeding VnE or max gross weight.    But instead of a cannula, if you literally stick the end of the hose up your nose, as far as I know, that isn't prohibited.  Is it a worse solution? Yes.  Is it legal?  Maybe?

 

Does every product you use have a requirement to be 'certified' or 'allowed' for use in the particular way you are using it in order to be legal?   No.....  If you want to wear your underwear on the outside of your pants and fly around, I doubt the FAA's complaint would be that you were using your fruit-of-the-looms incorrectly.   No matter how much absolutely every one of us wishes you didn't do that.  Or make up your own example of something that doesn't have a clearly defined use guideline.

What about using your Ferrari gloves for flying, when the manufacturer says "For use only when driving Ferrari automobiles." ?  I bet the FAA wouldn't violate anyone for that.  But it's closer to the oxygen concentrator example

What about using an oxygen concentrator that has been certified for non-aviation purposes?    Can you use that?  What if it says that it's usable by 2 people up to 10,000' and 1 person up to 14,000', but doesn't explicitly say it's prohibited otherwise?  What if it says nothing at all?  What if all there is for this is marketing copy but nothing in the manual?

Bah... All of this is pretty meaningless.   Unless or until there is some sort of problem, pilots are generally free to do what they want.  You want to use a concentrator?  You want to split it between two of you at 15,000' ?  Want to use a pulse oximeter?   Unless someone can provide authoritative guidance that says you can't, I say go for it.  Please be safe.

 

 

 

 

5 hours ago, Aaviationist said:

we also know that the most popular sensors tend to be inaccurate at concentrations below 95% so we don’t REALLY know in this example. 

[citation needed]