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.