N370MM NTSB Final Report

[Yetti]

If we are fixing things via sensors.  Have a Oxygen meter strapped to your finger that if it goes below a certain level, it fires the autopilot down to 7000 feet.  Computers are better at this than hypoxic people

[Jerry 5TJ]

2 hours ago, rbridges said:

I'm ashamed to ask this question since I work in the medical field, but how much oxygen is available at 25k feet?  I guess you pass out and revive at lower altitudes?  How long can you be "passed out" at that altitude with no ill effects?

At 25,000' the atmospheric pressure is about 5.5 psi, compared to 14.7 psi at sea level. 

The partial pressure of O2 at sea level is ~20% of 14.7 or a bit under 3 psi.  So at 25,000' breathing nearly 100% O2 (some air leaks around the typical mask) you can still have sea level partial pressure of O2 and get to 100% oxygen saturation.   

If you pass out and continue breathing air at 5.5 psi the O2 partial pressure is only ~1 psi so your body depletes O2 & after a time there's no recovery.  

There is an interval between the end of TUC and actual unconsciousness that varies with altitude and individual.   My one altitude chamber ride showed TUC at 25,000' of a few minutes followed by another few minutes of "useless consciousness" before the average person slumped over and  "passed out." 

Recovery was quick but not instant, perhaps 15-30 seconds to again reach useful consciousness once the instructor clapped their O2 mask on.  

Obviously the chamber ride didn't take anyone to fatal limits.  

My impression was that TUC is followed by an approximately equal interval of "useless consciousness"  then several more  intervals before it approaches irreversible.   

All that is moot because after TUC passes only an unimpaired copilot or an automatic descent can save you.  

I'm a reasonably fit non-smoker but at my age (64) I suspect my TUC is somewhat less than the chart predictions:   Perhaps half the table value if I exert myself some to reach around, get the mask, and turn on the backup O2 cylinder.  

So at 25,000' I need to recognize the problem, get the mask on, sealed and delivering 100% oxygen -- all in about  one minute.  

I doubt I can consistently achieve that.  Therefore I don't fly unpressurized and solo that high.

 

 

 

[aviatoreb]

3 hours ago, Jerry 5TJ said:

At 25,000' the atmospheric pressure is about 5.5 psi, compared to 14.7 psi at sea level. 

The partial pressure of O2 at sea level is ~20% of 14.7 or a bit under 3 psi.  So at 25,000' breathing nearly 100% O2 (some air leaks around the typical mask) you can still have sea level partial pressure of O2 and get to 100% oxygen saturation.   

If you pass out and continue breathing air at 5.5 psi the O2 partial pressure is only ~1 psi so your body depletes O2 & after a time there's no recovery.  

There is an interval between the end of TUC and actual unconsciousness that varies with altitude and individual.   My one altitude chamber ride showed TUC at 25,000' of a few minutes followed by another few minutes of "useless consciousness" before the average person slumped over and  "passed out." 

Recovery was quick but not instant, perhaps 15-30 seconds to again reach useful consciousness once the instructor clapped their O2 mask on.  

Obviously the chamber ride didn't take anyone to fatal limits.  

My impression was that TUC is followed by an approximately equal interval of "useless consciousness"  then several more  intervals before it approaches irreversible.   

All that is moot because after TUC passes only an unimpaired copilot or an automatic descent can save you.  

I'm a reasonably fit non-smoker but at my age (64) I suspect my TUC is somewhat less than the chart predictions:   Perhaps half the table value if I exert myself some to reach around, get the mask, and turn on the backup O2 cylinder.  

So at 25,000' I need to recognize the problem, get the mask on, sealed and delivering 100% oxygen -- all in about  one minute.  

I doubt I can consistently achieve that.  Therefore I don't fly unpressurized and solo that high.

 

 

 

How high do you fly?

[Jerry 5TJ]

23 minutes ago, aviatoreb said:

How high do you fly?

I haven't been solo above 17,000 this century in unpressurized aircraft.  

Others may do so safely but I decided long ago not to go into FL in unpressurized planes. 

 

 

[bradp]

I did recently watch a video about an autopilot that required a response from the pilot every x minutes or a descent would automatically be initiated (something from Garmin).  This plus an O2 saturation alarm with some sort of feed forward oxygen delivery loop would be the only methods by which I’d feel comfortable flying in the flight levels in an unpressurized aircraft.  

[carusoam]

Keep up the discussion...

Oxygen is needed to make simple decisions.  At the point you notice running out of O2, the cognitive skills may not be there to do any troubleshooting.

That may include looking at the pressure gauge and not recognizing it pointing to empty.  Last you knew it was full up. Now a lingering question of how did it get empty, that gauge can't be right.... clouds drift in, What was clear thinking, just a few minutes earlier...

If simple math is needed to calculate a descent...or turn to a heading.... don't expect it to be there...

The heart and brain both like their O2. Do whatever it takes to keep them served....

I like the discussions you all are taking part in...

• known procedures/hardware for automated descent.
• secondary systems that are ready to go, no assembly required.
• Primary systems that are as fail safe as possible.
• Avoidance.  Altitudes above 20k’ have such little TUC.
• When it comes to TUC, you may not have been given the warning that the TUC clock has started.
• Interesting actual use of partial pressure of O2 in air.
• Impact with the water at M20TN speeds while descending are bad.  An automated system that trims things for landing a slower flying speed could be helpful...

Similar Mooney experience came from @DanM20C's CO poisoning experience...  Take off, to unconsciousness, was about 15 minutes. (?) similar logic challenges lingered after he was on the ground.  CO is hard to displace even with pure O2 being delivered...

Back in the day, I noticed a couple of low O2 symptoms of my own while flying for more than an hour at 12k’...

 

Best regards,

-a-

 

 

 

[gsxrpilot]

Some don't fly unpressurized in the flight levels.
Some don't fly IFR
Some don't fly singles at night
Some don't fly small airplanes
Some don't fly

It's all risky... but there's a reason I fly a 252 and it's not to stay low.

Flying home to Austin from San Francisco late one night, IFR, I was comforted by the time and options that FL250 over the Sierra Nevada's and FL210 over west Texas would give me. The flight ended very uneventfully and on schedule just before 1am safely back in my hangar at KHYI.

[DanM20C]

36 minutes ago, carusoam said:

 

Similar Mooney experience came from @DanM20C's CO poisoning experience...  Take off, to unconsciousness, was about 15 minutes. (?) similar logic challenges lingered after he was on the ground.  CO is hard to displace even with pure O2 being delivered...

 

 

After reviewing the ATC transcripts I determined it was only 4-1/2 min from take off to deep slumber. I would guess only the first min would fall under “useful conciseness”. I was aware of a problem after that but didn’t have the cognitive ability at that point to trouble shoot and take action. 

Unfortunately Maj. Mari Metzler was called away on assignment and missed the Mooney Summit this year.  She was going to present on CO Poisoning and hypoxia/altitude sickness.  I spoke with her on the phone before the summit and she urged me to never fly my mooney in the Flight Levels.  She said she was hoping to convince everyone at the summit to consider giving up flying above 18k.  I didn’t ask her to elaborate as I thought I would get to hear her at the Summit.  For the past several years she has been focused on hypoxia and altitude sickness in the air force. I suspect she has some compelling evidence.  Hopefully she can make the Summit next year. 

I plan on keeping my 231 bellow 18k for now.  If my airplane was equipped with alt preselect, like @gsxrpilot, I would consider going higher. 

Cheers,

Dan

[DanM20C]

16 hours ago, pinerunner said:

A personal blood oxygen level meter would have offered a way to catch this. They're apparently not very expensive and fit over your finger. You might even be able to rig one up so it sets off an alarm (Sleep Monitor CMS50FW by Contec) if it goes below a certain level. If I mess with higher altitudes I think I'll get one.

Get a pulse Ox.  I  routinely flew between 9 an 11K without one. After my first flight with a pulse OX I ordered a potable O2 system.  I now use O2 when my sats get bellow 92%. Some times that is as low as 8K and other times is at 12K.  Everyone is different too, a good friend of mine (fellow pilot, and airplane owner, sort of.. Cessna) will usually be 10% below my readings when at alt.  If he concentrates and takes slow deep breaths he makes up some of the 10% but is never as high as me.   He is a fit, non smoker, in his 30’s.  

Cheers,

Dan

[Jerry 5TJ]

I use a pulse ox meter and adjust to mid 90s saturation.   That generally requires less flow than the "floating ball" meter suggests. 

Dont forget density altitude is what your lungs experience, not MSL.  On warm days in the Southwest I have been at 9,000 when DA is above 12,000.  

[Jerry 5TJ]

5 hours ago, gsxrpilot said:

....It's all risky... but there's a reason I fly a 252 and it's not to stay low....

That's fine, and I applaud the utility you are getting out of your 252.  It's your choice.  

The point of the thread is only that if your O2 system fails at FL250 and you are solo, you likely will not survive.  

My choice is to fly pressurized at up to FL280.  I know if the cabin goes "poof" I must get the mask on and working as job 1.  

 

 

[BradB]

@exM20K The mountain high O2D2 will alarm if you stop breathing.  It will also alarm if the flow of oxygen stops.   But the alarm is high pitched and not all that audible with noise canceling headphones.   I keep a pulse ox and check mine frequently in the FL’s.   

If you have one of the carbon monoxide detectors that it’s popular in another thread, the volume seems similar to that with headphones on.

Brad

 

 

[mike_elliott]

6 hours ago, DanM20C said:

After reviewing the ATC transcripts I determined it was only 4-1/2 min from take off to deep slumber. I would guess only the first min would fall under “useful conciseness”. I was aware of a problem after that but didn’t have the cognitive ability at that point to trouble shoot and take action. 

Unfortunately Maj. Mari Metzler was called away on assignment and missed the Mooney Summit this year.  She was going to present on CO Poisoning and hypoxia/altitude sickness.  I spoke with her on the phone before the summit and she urged me to never fly my mooney in the Flight Levels.  She said she was hoping to convince everyone at the summit to consider giving up flying above 18k.  I didn’t ask her to elaborate as I thought I would get to hear her at the Summit.  For the past several years she has been focused on hypoxia and altitude sickness in the air force. I suspect she has some compelling evidence.  Hopefully she can make the Summit next year. 

I plan on keeping my 231 bellow 18k for now.  If my airplane was equipped with alt preselect, like @gsxrpilot, I would consider going higher. 

Cheers,

Dan

Dan, Mari (Mars) is a fixture at the Mooney Summit, and yes, it was unfortunate she was called away at the last minute. She always provides entertaining and insightful seminars on physiology of pilots. Thats her day job also. She is involved with  hypobaric chamber at Tyndall, and regularly sees that our boys that fly the F22's are fit to fly. As a pilot herself, she knows what we are facing. She really gets how dangerous it is for the human body, not just the lack of O to be in the FL's . She is just one of the people that convinced me to keep the Bravo out of the FL's and did so with empirical data, not just suggestive opinion. She is a very smart, pleasant professional. She will be back at the Summit's

[aviatoreb]

1 hour ago, mike_elliott said:

Dan, Mari (Mars) is a fixture at the Mooney Summit, and yes, it was unfortunate she was called away at the last minute. She always provides entertaining and insightful seminars on physiology of pilots. Thats her day job also. She is involved with  hypobaric chamber at Tyndall, and regularly sees that our boys that fly the F22's are fit to fly. As a pilot herself, she knows what we are facing. She really gets how dangerous it is for the human body, not just the lack of O to be in the FL's . She is just one of the people that convinced me to keep the Bravo out of the FL's and did so with empirical data, not just suggestive opinion. She is a very smart, pleasant professional. She will be back at the Summit's

How high do you fly Mike?

[mike_elliott]

Just now, aviatoreb said:

How high do you fly Mike?

I am very comfortable at 17K and less now days in unpressurized. I am also old, and not in that big of a hurry. Even so, hypoxia is a real danger above 10K in our planes. I carry a portable bottle also. My mask also hurts to wear for any length of time.

[aviatoreb]

43 minutes ago, mike_elliott said:

I am very comfortable at 17K and less now days in unpressurized. I am also old, and not in that big of a hurry. Even so, hypoxia is a real danger above 10K in our planes. I carry a portable bottle also. My mask also hurts to wear for any length of time.

So when people say they avoid the flight levels, what does this mean? FL17?  Or are they saying the 20s?

I often go 17/18, and rarely have I been above 19, specifically because it feels "spooky" at 20+ in the sense that I am hyper aware of how inhospitable it gets as you go up from there.  I have not been working it as a problem as a "line in the sand" not to cross though, but I am thinking about it.  I am in excellent cardio health, as far as they come, for an aging graying, stereotypical ga pilot dude.

I have also been thinking about, for reasons of pure convenience, to let my standard 3rd class medical go when it is time next summer, and then go with the new medical standard that came out - the only thing extra that I can do with the 3rd class medical that I couldn't otherwise do is to fly 18 and above, which maybe we should all decide isn't a good idea anyway.

I love flying between 14 to 18 on the east coast, since it is very quiet there.  To high for most GA, and too low for the jets.  In the north east corridor, I nonetheless get really good routing, and very rarely need to be pointed out traffic.  Plus the turbo gets to be pretty fast there.  But even so, I sometimes will fly in the mid teens into a strong headwind for the other reason I like to fly high - like I fly direct over our local mountains (Adirondacks) and high teens over the lakes, even into a headwind, since I am thinking gliding distance, that altitude/glide distance is the parachute.

My feeling is that at 17 I might have a good chance to react and descend if need be, and I have tested this with a copilot at my side.  Much higher - and maybe not.  So I choose altitudes accordingly.

 

[donkaye]

7 hours ago, Jerry 5TJ said:

I use a pulse ox meter and adjust to mid 90s saturation.   That generally requires less flow than the "floating ball" meter suggests. 

Dont forget density altitude is what your lungs experience, not MSL.  On warm days in the Southwest I have been at 9,000 when DA is above 12,000.  

If I remember correctly, according to Dr. Bob Achtel it is Pressure Altitude that is important, not Density Altitude.

[donkaye]

On 10/23/2017 at 10:08 AM, exM20K said:

Thinking seriously about a MH O2D2, which will alarm if you quit breathing.  I just haven't figured out how to mount it into the ceiling O2 ports of the M20TN factory system without creating a forest of tubes.  Any tips on where to mount these devices so the alarms are useful but they are not in the way?

-de

I wouldn't think too hard about it, Dan.  On the recommendation of a student I bought one.  To make a long story short, I couldn't get my O2 sats above 92% even on the highest flow rate.  I spent the first hour of the first and only flight with it being completely distracted with the O2 system.  Additionally, the noise of breathing coming through the headset was annoying and distracting.  I disconnect the system and never used it again.  Since we were on our way to Oshkosh this year with it, I went to the MH booth.  They were every nice and I left the system with them to check it out.  After I got back home they called and said the system worked.  I said it didn't.  Awhile later they called and said it wasn't set up for an airplane that had an altitude compensating regulator like we have on the Bravo.  They refunded most of my money, but kept a 10% restocking charge.   I like the MH connectors and set up my backup O2 system with their regulator and connectors.

Another VERY important considerations when flying in the FL in an unpressurized airplane concerns the possibility of getting the Bends.  My SO has that tendency.  For her it would be worse than getting into a thunderstorm.  When I first got the plane, I didn't even know about the Bends in airplanes.  It took awhile and many conversations with people at UND and Brooks AF Medical Center in San Antonio to figure it out.  Dr. Bob Achtel in his "Into thin Air Course" goes over mitigations extensively.  For us time aloft is most important, then taking an aspirin 1 hour before flight, then keeping hydrated, and finally pre breathing O2 which isn't practical for us.  

On short flights I don't take the backup O2 bottle, but on any long cross country it goes along.  When I first got the plane I flew at FL 210 and 220 thinking I was a jet.  No longer.  15K to 17K gives me enough additional TAS and efficiency (the higher up the more efficient the airplane, since you're getting closer to best L/D).  Any time I'm going over 200 knots I'm a happy camper.

I also question the NTSB results.  On the high pressure side it would have been zero when he took off.  On the low pressure side without a kink in the line I don't see how the O2 could have leaked out so much in so little time.

 

[Piloto]

Another clue for lack of oxygen in your blood is the color of your nails (un-polish). As you climb the nails will become darker.

Blue nails typically signal poor oxygen levels and lung diseases, such as pneumonia.

José

[Marauder]

So when people say they avoid the flight levels, what does this mean? FL17?  Or are they saying the 20s?
I often go 17/18, and rarely have I been above 19, specifically because it feels "spooky" at 20+ in the sense that I am hyper aware of how inhospitable it gets as you go up from there.  I have not been working it as a problem as a "line in the sand" not to cross though, but I am thinking about it.  I am in excellent cardio health, as far as they come, for an aging graying, stereotypical ga pilot dude.
I have also been thinking about, for reasons of pure convenience, to let my standard 3rd class medical go when it is time next summer, and then go with the new medical standard that came out - the only thing extra that I can do with the 3rd class medical that I couldn't otherwise do is to fly 18 and above, which maybe we should all decide isn't a good idea anyway.
I love flying between 14 to 18 on the east coast, since it is very quiet there.  To high for most GA, and too low for the jets.  In the north east corridor, I nonetheless get really good routing, and very rarely need to be pointed out traffic.  Plus the turbo gets to be pretty fast there.  But even so, I sometimes will fly in the mid teens into a strong headwind for the other reason I like to fly high - like I fly direct over our local mountains (Adirondacks) and high teens over the lakes, even into a headwind, since I am thinking gliding distance, that altitude/glide distance is the parachute.
My feeling is that at 17 I might have a good chance to react and descend if need be, and I have tested this with a copilot at my side.  Much higher - and maybe not.  So I choose altitudes accordingly.
 

I think the answer to your first question should be based on your own physiological response based on a real experience inside a chamber.

I can tell you having flown a number of passengers over the years, some of those passengers sleeping at 11,000 feet were probably sleeping because of low O2 saturation levels.

I don’t have a turbo but do like to fly higher on cross country than most GA pilots without turbos fly. I can also tell you monitoring my O2 levels, that when I am at 9 or 10k, I’m running lower 02 saturation levels than I want to be at. I also know that toking on supplemental O2 lowers my chance of getting a headache.

I remember an accident of a co-worker who is a flatlander. We had a meeting in Colorado at a hotel. He got up in the middle of the night to go to the bathroom and found himself on the floor the next morning with a gash on his head from passing out and hitting the dresser.

Everyone responds differently to lack of oxygen. Probably best to understand that before embarking in those rarified air flights.


Sent from my iPhone using Tapatalk Pro

[aviatoreb]

10 minutes ago, Marauder said:

 

I think the answer to your first question should be based on your own physiological response based on a real experience inside a chamber.

I can tell you having flown a number of passengers over the years, some of those passengers sleeping at 11,000 feet were probably sleeping because of low O2 saturation levels.

I don’t have a turbo but do like to fly higher on cross country than most GA pilots without turbos fly. I can also tell you monitoring my O2 levels, that when I am at 9 or 10k, I’m running lower 02 saturation levels than I want to be at. I also know that toking on supplemental O2 lowers my chance of getting a headache.

I remember an accident of a co-worker who is a flatlander. We had a meeting in Colorado at a hotel. He got up in the middle of the night to go to the bathroom and found himself on the floor the next morning with a gash on his head from passing out and hitting the dresser.

Everyone responds differently to lack of oxygen. Probably best to understand that before embarking in those rarified air flights.


Sent from my iPhone using Tapatalk Pro

 

Good comments.

But one of my questions was what do people mean when they say the flight levels.  Not what is the best choice.  Since the way some people seem to use the phrase, I think it is upper teens and above.  Others seem to mean anything above the 12500 rule.  Others seem to mean just 20's and above.  So it is sort of a person specific phrase and therefore sort of useless to convey anything.

So I say "mid teens" or "upper teens" etc.

[TCC]

Good point. I’ve always considered FL180 (18000) as the bottom of the flight level since that’s what the military taught me. I know my hypoxia signs from multiple chamber rides, but still have a hard time justifying being above FL180 in an unpressurized aircraft. Not condemn anyone comfortable there, just my personal limit from having spent a lot of time in the 11K-14K band walking up, down, and around really big rocks with no supplemental O2

[LANCECASPER]

1 minute ago, TCC said:

Good point. I’ve always considered FL180 (18000) as the bottom of the flight level since that’s what the military taught me. I know my hypoxia signs from multiple chamber rides, but still have a hard time justifying being above FL180 in an unpressurized aircraft. Not condemn anyone comfortable there, just my personal limit from having spent a lot of time in the 11K-14K band walking up, down, and around really big rocks with no supplemental O2

Yes, Flight Levels begin at FL180 where you change altimeter to 29.92.

[yvesg]

I just purchased a portable O2 tank last week. It is getting certified this week. On long trips (in the past) I would borrow one from another Mooney owner but since I will have my own, I am more likely now to fly high due to the availability of the tank. 

My M20C is not turbo and I should set a personal limit (also aircraft limit) somewhere between 15K and 17K. My question is: If I fly at 17K and have an O2 failure, how useful would be a backup emergency cannister (like the ones suggested above)? Is the useful conciousness long enough at that altitude to allow emergency descent below 10K without the need of such a thing?

Thanks.

Yves

[donkaye]

17 minutes ago, yvesg said:

I just purchased a portable O2 tank last week. It is getting certified this week. On long trips (in the past) I would borrow one from another Mooney owner but since I will have my own, I am more likely now to fly high due to the availability of the tank. 

My M20C is not turbo and I should set a personal limit (also aircraft limit) somewhere between 15K and 17K. My question is: If I fly at 17K and have an O2 failure, how useful would be a backup emergency cannister (like the ones suggested above)? Is the useful conciousness long enough at that altitude to allow emergency descent below 10K without the need of such a thing?

Thanks.

Yves

Slightly greater than 20 minutes, so you would have plenty of time to get down if you recognized your symptoms soon enough.  At that altitude it is pretty easy to recognize your symptoms within a minute.  On a ferry flight at 17K I had multiple O2 tanks with which I was not familiar.  Not realizing which way was on on one of them because of the way they were hooked together, I got it backwards. Within a minute I recognized my particular symptom and did a Pulse Oximeter check.  It was 85%.  I turned the knob the other way and all was quickly good again.