What altitude is the M20K 252/Encore certified for?

[Fix]

What altitude is the M20K 252 certified for?

M20K 231, has 25000 feet, listed in POH.
M20K 252 has 28000 feet, listed in POH.
M20K Encore has 25000 feet, listed in POH.

What do an upgraded M20K 252 with Encore mod have?

25000 feet or 28000 feet?

I'm looking on a uAvionix AV-30-C and this has a limitation for any aircrafts that are certified above 25000 feet.
They list M20K in their AML, but has a note about the 25000 feet limit.
 

[Pinecone]

25,000

Here is the cite from my POH (252 converted to Encore)

[Aerodon]

The Encore conversion requires replacement of the POH with an Encore POH.  So limitations like RPM. MP and max operating altitude written in the new POH apply.

 

Aerodon

[LANCECASPER]

You really don't want to go up to FL280 in a Mooney. Although it was legal once it was certified,  it would never be certified that way today and it just isn't smart. It's a very inhospitable environment up there. You have 10 minutes of useful consciousness at FL220 and only 2.5 minutes at FL280. 

https://en.wikipedia.org/wiki/Time_of_useful_consciousness

Foolishly, 30 some years ago in a 231 and then a couple years later in my first Bravo I used to go up FL250 all the time with the onboard oxygen with no backup and pulse oximeters weren't a thing back then. Then in 1999 the Payne Stewart accident turned the spotlight on the challenges and risks of flying in the flight levels and I began to re-evaluate on whether what I had been doing was a good idea. From that point on I had always had backup oxygen.

Realistically, flying the the teens gives you a great place to fly very little traffic and your options to get down safely are greater. Higher can be done but you really have to be aware of all of the risks and take it very seriously.

[kortopates]

You really don't want to go up to FL280 in a Mooney. Although it was legal once it was certified,  it would never be certified that way today and it just isn't smart. It's a very inhospitable environment up there. You have 10 minutes of useful consciousness at FL220 and only 2.5 minutes at FL280. 
https://en.wikipedia.org/wiki/Time_of_useful_consciousness
Foolishly, 30 some years ago in a 231 and then a couple years later in my first Bravo I used to go up FL250 all the time with the onboard oxygen with no backup and pulse oximeters weren't a thing back then. Then in 1999 the Payne Stewart accident turned the spotlight on the challenges and risks of flying in the flight levels and I began to re-evaluate on whether what I had been doing was a good idea. From that point on I had always had backup oxygen.
Realistically, flying the the teens gives you a great place to fly very little traffic and your options to get down safely are greater. Higher can be done but you really have to be aware of all of the risks and take it very seriously.

All excellent info Lance and I’ll add i never understood how the FAA let Mooney certify the ceiling at 28K when the installed O2 system is certified and approved only to 25K. We’re suppose to have the much more expensive diluter-demand O2
system above 25K!


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[Falcon Man]

Having flown my K models into the fight levels on a couple of occasions (once to get on top and a couple of times to see what the performance is like @ max HP), I learned a few things.

I discovered that to keep my O2 sat's above 90% I had to use two oxygen ports - one for nose cannula and another for the big blue mask with the mike over the cannula.

Also, I tried to hand fly at 23-25K and it was nearly impossible to trim for level flight. A functional autopilot was needed to maintain altitude.

On one flight the grease froze on the elevator drive, and after descending to warmer weather with reduced power, it defrosted.

I do not plan on repeating these types of flights. I wholeheartedly agree that flights in a K model between 15-18K are the sweet spot for efficient performance, safety and less turbulence.

[kortopates]

Having flown my K models into the fight levels on a couple of occasions (once to get on top and a couple of times to see what the performance is like @ max HP), I learned a few things.
I discovered that to keep my O2 sat's above 90% I had to use two oxygen ports - one for nose cannula and another for the big blue mask with the mike over the cannula.
Also, I tried to hand fly at 23-25K and it was nearly impossible to trim for level flight. A functional autopilot was needed to maintain altitude.
On one flight the grease froze on the elevator drive, and after descending to warmer weather with reduced power, it defrosted.
I do not plan on repeating these types of flights. I wholeheartedly agree that flights in a K model between 15-18K are the sweet spot for efficient performance, safety and less turbulence.

Maybe you need to get the altitude compensating stage of your O2 regulator function tested the next time you change out the bottle or have it hydro tested. Never had any of those problems. Agree about the sweet spot but sometime you may want the capability to top weather.

My wife, a retired high altitude mountaineer, can keep her pulse sat in the low 90’s just using the cannula, but i can’t and need the mask at 17K and up so it also could be a personal thing rather than equipment.


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[Falcon Man]

I don't have those airplanes any more so cannot now verify if there was an equipment problem, so it's a good point. I haven't ventured above 19K in my current 252 and either the cannula or mask works fine, both at the flow rate much less than indicated for the altitude, yet with acceptable O2 sats.

Living in the intermountain west @ 5,300 ft elevation I use O2 on every cross country flight because of all the mountains surrounding my home airport and have to be over 12,500 for safe altitude operations. I can use a cannula in the teens but prefer the mask for comfort with the O2 flow setting at the lowest.

Interesting point about flying on top in the flight levels. Here in the mountains that's nearly impossible because of the regular icing forecasts when there is IFR conditions.

[cliffy]

There are 4 types of hypoxia-

 

• Hypoxic Hypoxia (also known as Hypoxemic Hypoxia):

  Occurs due to a lack of oxygen in the blood, often caused by breathing air with insufficient oxygen, high altitude, or lung problems.
• Anemic Hypoxia (also known as Hypemic Hypoxia):

  Results from the blood's inability to carry enough oxygen, often due to low red blood cell count (anemia) or carbon monoxide poisoning.
• Stagnant Hypoxia (also known as Circulatory Hypoxia):

  Occurs when blood flow is insufficient to deliver oxygen to the tissues, potentially due to heart problems or shock.

  Histotoxic Hypoxia:

  Occurs when the cells are unable to use the oxygen delivered to them, often due to poisoning (like cyanide) or metabolic problems.

   

  We are only concerned, as pilot's, with the first 2-  Hypoxic  and Anemic Hypoxia

  We can dispose of the Anemic Hypoxia by saying we won't see that unless we succumb to Carbon Monoxide poising. 

   

  HYPOXIC HYPOXIA is our nemesis. It is a sneaky little bastard!  You may never realize you are compromised until its too late.

  JMO Unless you have been through an altitude chamber ride you have no business flying where you need oxygen!

  A short reflection- One of my chamber ride my partners  took off his mask as I monitored him. He did the drills the Instructor was 

  calling for for about 2 mins (25,000') at which time I saw he needed to put his ask back on. I told him to put it on to which he said OK

  He didn't reach down to put it on. I asked again to the same response, After the 3rd request he "rolled over" and I put it on him and he recovered in less than a minute. 

  You can be hypoxic, know full well you are hypoxic but not have the mental acuity to fix the issue. 

  If you think you are safe with a second source you may never get  the chance to transfer the supply.

  Never let that sneaky little bastard HYPOXIA jump on you.  You may not get a second chance. 

  Even IF you get your second supply working - GO LOWER NOW.

   

  One hard and fast rule to remember- IF you suffer an O2 problem (n matter how slight the interruption is) immediately start a max effort descent. The longer you try to "fix" the issue the closer you are to going to sleep- permanently. 

  Do not pass GO, DO NOT ASK FOR LOWER, DO NOT ASK PERMISSION TO GO LOWER- just get your arse down NOW

  Or you might not be able to collect the $200. .

  It is a for real emergency- time is of the essence.  

  Talk to ATC AFTER you are going down hell bent for leather. Not before. 

  We can find several hypoxic events on utube that ended in tragedy just because the pilot waited TO ASK PERMISSION TO GO LOWER! 

  In all 3 of my pressurization loss incidents at altitude I was going down at 6.000 fpm before I even tried calling ATC. 

   

  Thought to remember- the TUC tables (time of useful conscience) were made with young healthy military pilots- NOT those of us

  50+ and over weight. Take those times with a grain of salt!

   

  My first AME many years ago was the Doc who got cannulas certified for aviation - and ONLY to 18,000'

  After 18.000' we are required to go on the proper  mask.

  JMO again- going above 18,000' in our unpressurized airplanes is flirting with big problems. 

   

  Another thought-  IF your O2 supply dies and you take a minute to realize it-

  How long will it take you to get down to 10,000'?  How fast can you descend?

  Can you do 1,000 fpm constantly? Can your airplane do 2,000 fpm below the red line? Can you do 2,000 fpm constantly?

  Will you be conscious when you pass 10,.000? How long did you wait up there before you decided to try and get down?

   

  In doing many many sim training flights giving pilots a pressurization failure problem  the vast majority of crews

  failed to maintain the required max descent rate the first time it was tried. Most all of them shallowed out the descent 

  as soon as the speed picked up. You will too if you haven't practiced it. 

   

  25,000' at 2,000 fpm is 6 mins + getting down to 10.000'  IF your O2 fails to deliver.  You'll be 3 mins above 18,000'

  minimum- IF you can maintain a 2,000 fpm average descent. That's a big IF!

   

  Now a bit of history- Later in WWI young, healthy fighter pilots flew their fighters up to 20,000 ft and stayed there

  for an hour or more routinely, BUT they complained of headaches and malaise upon returning to earth.  

   

  As a famous TV program used to caution-  Ya'll be careful out there!

   

   

[Pinecone]

19 hours ago, kortopates said:

All excellent info Lance and I’ll add i never understood how the FAA let Mooney certify the ceiling at 28K when the installed O2 system is certified and approved only to 25K. We’re suppose to have the much more expensive diluter-demand O2
system above 25K!

USAF required pressure breathing above 25,000 if not pressurized.  That was the altitude limit on the T-37 for this reason.

[jlunseth]

The service ceiling of the 231

On 3/26/2025 at 1:57 PM, Fix said:

M20K 231, has 25000 feet, listed in POH.
M20K 252 has 28000 feet, listed in POH.
M20K Encore has 25000 feet, listed in POH.

 

The service ceiling of the 231 is 24,000. At least that is the ""Maximum operating altitude" in my POH. You aren't going to get much higher anyway. The critical altitude is 22,5, give or take depending on day temps, even with the Merlin, and with the MP knob all the way in and the MP dropping the climb rate is very anemic. I went there once to say I did it, so now I have done it and don't have to do it again.

[Yooper Rocketman]

I spoke with a Spruce Creek, FL friend that attended a Bonanza Society Clinic in Daytona, FL this winter where they discussed high altitude flying and the dangers.  The presenter was an AME and an ex military flight surgeon, and was running a business specializing in aero medicine.  He stated he didn't want ANYONE flying above 15K except for short (an hour max times for topping weather) while in an unpressurized GA airplane.  My friend told me because he knew I routinely fly from the U.P. of Michigan to Spruce Creek Air Park (10 miles south Daytona) in my M20K Rocket in the FL's.  I listened to his information but thought it was a bit over the top.  My next flight home, at FL210, I encountered "itching across my chest and arm pits" and noticed after landing, my chest was showing blue on the skin.  I mentioned this to my Bonanza friend, who's wife was a RN, and a few days later he approached me after discussing that with her and said that was a condition, similar to the bends from diving, that derived from high altitude exposure.  The condition is called HAPH, High Altitude Pulmonary Hypertension.

So, on my next trip down to Florida, with winds really advantageous at FL230 (and my first hour+ needs to be in the FL's to get over Laker Michigan safely) I filed and flew up there.  No issues in the first 90 minutes but then I notice the same arm pit and chest itching, and NOW my wife, extremely concerned, is noting the same symptoms.  I asked Indy center for 15K immediately and, within 20 minutes of leveling at 15k, our symptoms went away.  

We HAVE flown since at FL180 with no issues, but I no longer fly above FL180 for more than an hour or so.

Can't wait until I get my pressurized Lancair IVPT flying again !!!

Tom Sullivan

[dkkim73]

16 minutes ago, Yooper Rocketman said:

No issues in the first 90 minutes but then I notice the same arm pit and chest itching, and NOW my wife, extremely concerned, is noting the same symptoms.  I asked Indy center for 15K immediately and, within 20 minutes of leveling at 15k, our symptoms went away.  

We HAVE flown since at FL180 with no issues, but I no longer fly above FL180 for more than an hour or so.

It's tricky doing medicine over the Internet, but what you describe falls into the general spectrum of decompression sickness ("the bends"). There're a broad range of manifestations, less and more serious, type I and type II, respectively. A bit discussing cutaneous symptoms is here: 

https://dan.org/health-medicine/health-resource/dive-medical-reference-books/decompression-sickness/diagnosing-dcs/

You might consider visiting with a doc who has some expertise in the area, ideally someone with a dive/hyperbaric certification. I never went to DMO training though I wish in retrospect I had. 

IIRC they will sometimes dive people after the fact. 

I will have to read a bit more and reflect on the comments earlier in the post where the flight doc recommended that restriction. That feels aggressive, though I've talked to a few other knowledgeable people that do not like flying the FLs in unpressurized aircraft. 

D

[wombat]

I take my Rocket up to FL210 every now and then.  And I've been up to FL230 for one long flight with 73 knot tailwinds.

Yes, there are some increased dangers at those altitude.  If you are new to it, I recommend you read "An Aviator's Field Guide to Middle-Altitude Flying"
By Jason Blair  https://www.aopa.org/news-and-media/all-news/2018/may/21/field-guide-to-middle-altitude-flying

 

I recommend at least one experience with hypoxia either as a non-required crewmember or in an altitude chamber where you can focus on the hypoxia and not on flying.

 

One thing I've noticed repeatedly in aviation is that people tend to upgrade to aircraft with increasing capabilities and safety throughout their flying career.   Then after they have upgraded to something more safe, they will decry everything less than their current budget permits as 'too dangerous'.  The FAA sets the standard for minimum safety.    If you want to be more safe, that's great for you.  I quite often want to be more safe myself but I won't argue if others want to do no more than follow the rules.

[Fly Boomer]

8 hours ago, wombat said:

Yes, there are some increased dangers at those altitude.  If you are new to it, I recommend you read "An Aviator's Field Guide to Middle-Altitude Flying"
By Jason Blair 

Thanks for the tip — I just ordered a copy.

 

[Pinecone]

10 hours ago, wombat said:

I recommend at least one experience with hypoxia either as a non-required crewmember or in an altitude chamber where you can focus on the hypoxia and not on flying.

I also HIGHLY recommend an altitude chamber or PROTE ride for anyone flying above 12,000 feet.  And not a bad idea for everyone.

[Will.iam]

On 4/25/2025 at 1:35 PM, Yooper Rocketman said:

I spoke with a Spruce Creek, FL friend that attended a Bonanza Society Clinic in Daytona, FL this winter where they discussed high altitude flying and the dangers.  The presenter was an AME and an ex military flight surgeon, and was running a business specializing in aero medicine.  He stated he didn't want ANYONE flying above 15K except for short (an hour max times for topping weather) while in an unpressurized GA airplane.  My friend told me because he knew I routinely fly from the U.P. of Michigan to Spruce Creek Air Park (10 miles south Daytona) in my M20K Rocket in the FL's.  I listened to his information but thought it was a bit over the top.  My next flight home, at FL210, I encountered "itching across my chest and arm pits" and noticed after landing, my chest was showing blue on the skin.  I mentioned this to my Bonanza friend, who's wife was a RN, and a few days later he approached me after discussing that with her and said that was a condition, similar to the bends from diving, that derived from high altitude exposure.  The condition is called HAPH, High Altitude Pulmonary Hypertension.

So, on my next trip down to Florida, with winds really advantageous at FL230 (and my first hour+ needs to be in the FL's to get over Laker Michigan safely) I filed and flew up there.  No issues in the first 90 minutes but then I notice the same arm pit and chest itching, and NOW my wife, extremely concerned, is noting the same symptoms.  I asked Indy center for 15K immediately and, within 20 minutes of leveling at 15k, our symptoms went away.  

We HAVE flown since at FL180 with no issues, but I no longer fly above FL180 for more than an hour or so.

Can't wait until I get my pressurized Lancair IVPT flying again !!!

Tom Sullivan

I wonder what that AME would say about mountain climbers that spend a week at 15,000ft base camp unpressurized and then climb to 29,000ft for hours on end? It’s not the altitude that causes the bends but the rate of change that is the issue. Also if you pre-breathe oxygen at lower altitudes before you climb your body will displace more of the nitrogen that is in your body which is the gas that gives you the bends. That’s really all the dive chamber is doing is putting you under more pressure to get the nitrogen bubbles to reabsorb into your blood and then allow the nitrogen to off gas out your lungs. This is facilitated by breathing oxygen while in the pressurized chamber thus helping to displace the nitrogen levels in your body.  By breathing oxygen down low before you climb is better than putting the oxygen on right before you leave 12,500ft as by then the nitrogen might already be starting to come out of the blood in your body than out your lungs depending on how quick you are climbing. 

[Pinecone]

When we did the altitude chamber rides in USAF UPT, we would pre-breath 100% O2 for 30 minutes before "climbing" to altitude.

I would say it is combo of RATE of change and MAGNITUDE of change.  Mountain climbers spending time at 15,000 reduces the magnitude of change for climbs to 29,000.

[hubcap]

I have flown Myrtle in the flight levels a few times, but honestly, the sweet spot, for the M20K 231, as has been mentioned, is somewhere between 15,000' - 18,000'. The few times I flew in the flight levels it was to take advantage of the tailwinds but honestly at the end of the day I doubt I will venture up there again. The juice just isn't worth the squeeze for me, and to @LANCECASPER's point, if I were going to fly in the flight levels, I would definitely have some type of back-up O2 system. Another thing that has been mentioned is the difficulty in hand-flying in the flight levels.....I wouldn't do it without a good autopilot.

[dkkim73]

6 hours ago, Pinecone said:

When we did the altitude chamber rides in USAF UPT, we would pre-breath 100% O2 for 30 minutes before "climbing" to altitude.

I would say it is combo of RATE of change and MAGNITUDE of change.  Mountain climbers spending time at 15,000 reduces the magnitude of change for climbs to 29,000.

All true. There are also physiological differences between humans, not only are some conditioned better but some tolerate it better due to varying protoplasm. Some people, from what I've read/heard (not personal rx) get repeatedly "bent". IIRC diving them can sometimes reduce recurrence. But I'm not sure of the time window for that. 

Physiology of breathing 100% O2 as someone else mentioned above, displace N2.  Astronauts will pre-breathe prior to"spacewalk" as the EVA suits runs lower pressure. So also high-altitude pilots (think Spooky types). And doing it for a chamber ride is just cheap insurance. I used to do this in the Eagle while waiting on the ground, which some people thought was weird. But hey, it's essentially free. 

There would be near-zero downside to breathing max O2 if you feel funny in flight, in this context, whether CO or something else. Unless maybe you're a COPDer or have some other altered physiology, in which case you should talk to your AME. 

I agree with above rec of a chamber ride. I think it's better than PROTE/ROBD as you get to experience more, but either is better than nothing. Done it multiple times, probably should do it again as I'm older now. 

DK

[Yooper Rocketman]

I'm ordering the book recommended previously as I post this.  That said, I am not new to high altitude flying; I have been doing it for 25 years, most of that time on O2 as well.  I didn't post to alarm anyone, nor to show a bias against high altitude (on O2) flying.  Actually, to the contrary.  My flights south to Florida in the winter up high get me above the weather and, almost always, a much faster ground speed.  My rebuild of my Lancair (pressurized) Turbine will surely take me a couple years, so flying high on O2 will be a desirable option for the near term future.  I'm thinking about pre-breathing for flights where I will be going up into the FL's to see if that helps.  

As far as the chamber ride, I'm not opposed to it at all, just not something I can easily arrange based on where I live.  I HAVE had 3 hypoxic events, (all equipment malfunctions) all of which my early symptoms were very obvious, consistent, and easy to detect.   Corrective actions were implemented immediately, and the outcome of all three were as expected and desired.  Only one ended with a phone call to ATC afterwards, because the Supervisor was concerned with the active controllers improper response, not mine (I went to 121.5 when the response was inadequate, but DID NOT need to immediately descend as I was improvising O2 directly into my face.  That said, I WOULD HAVE descended immediately had the circumstances warranted it).  A last note, I always fly with a pulse ox and regularly check my O2 saturations whenever on O2.  

I appreciate the responses from DK.  It's evident your background is appropriate and I find value in them.

Tom

[Will.iam]

8 hours ago, Yooper Rocketman said:

I'm ordering the book recommended previously as I post this.  That said, I am not new to high altitude flying; I have been doing it for 25 years, most of that time on O2 as well.  I didn't post to alarm anyone, nor to show a bias against high altitude (on O2) flying.  Actually, to the contrary.  My flights south to Florida in the winter up high get me above the weather and, almost always, a much faster ground speed.  My rebuild of my Lancair (pressurized) Turbine will surely take me a couple years, so flying high on O2 will be a desirable option for the near term future.  I'm thinking about pre-breathing for flights where I will be going up into the FL's to see if that helps.  

As far as the chamber ride, I'm not opposed to it at all, just not something I can easily arrange based on where I live.  I HAVE had 3 hypoxic events, (all equipment malfunctions) all of which my early symptoms were very obvious, consistent, and easy to detect.   Corrective actions were implemented immediately, and the outcome of all three were as expected and desired.  Only one ended with a phone call to ATC afterwards, because the Supervisor was concerned with the active controllers improper response, not mine (I went to 121.5 when the response was inadequate, but DID NOT need to immediately descend as I was improvising O2 directly into my face.  That said, I WOULD HAVE descended immediately had the circumstances warranted it).  A last note, I always fly with a pulse ox and regularly check my O2 saturations whenever on O2.  

I appreciate the responses from DK.  It's evident your background is appropriate and I find value in them.

Tom

Maybe invest in an oxygen concentrator? I got inogen G5 used for $1200. I start breathing on that right after takeoff and it is good til 18k on one person. If i have a second person they claim it would be good to 14k. At least that way you already lowered your nitrogen levels and have not used any of your ships O2 until the inogen can’t keep up and if you had a malfunction of main ship O2 you could get on the inogen at 18k or lower to keep your wits about you as you came down to safer altitudes if you had a passenger with you. Maybe an option for you?

[Pinecone]

Years ago three of us (all pilots) were headed to upstate NY in a rented 182.  Due not being able to find any current charts (exact day of expiration), we had to go VFR.  To get over some weather, we had to go to 13,500 for a short period (less than 30 minutes).

I was in the left front seat.  The pilot in the left front was flying under the hood (working to CFII).  

I was fine, but I noticed the left seat guy's head was bobbing around.  And he was a bit sloppy flying.  I look in the back and that person was OUT.  I realized they were both hypoxic.  Again, I had no hypoxia symptoms.  They did not see the issue themselves as they had never done a chamber ride or flown high enough to experience their symptoms.

If you fly on O2, you REALLY should do a chamber or PROTE ride.  It could be life saving.  Not only your life, but of those flying with you.

[wombat]

10 hours ago, Pinecone said:

If you fly on O2, you REALLY should do a chamber or PROTE ride.  It could be life saving.  Not only your life, but of those flying with you.

I have also just taken pilots up to 17,999' (You can go higher if you want to be IFR) so they can experience it in real life.   I'm on O2, but they are not a required flight crewmember, so it's up to them.

[Pinecone]

As per my story, many people don't even need to go that high.

I was the outlier the other way.  During one of our chamber rides, they had every other person take off their mask at 25,000 foot pressure altitude.  This was for you to see YOUR hypoxia indicators.  During this time, you did simple math, copy sentences.  I was the one that was doing fine without 02.  They finally gave up on me and had my put my mask on.   My paper with writing was a bit more scrawled, but readable.

These days though, I can see some mild symptoms in the 9 - 10K range.  Getting old sucks.