Welcome Guest. Sign in or Signup

5 Answers

Supplemental oxygen in non-pressurized craft.

Asked by: 2185 views , , , , ,
Aircraft Systems, Commercial Pilot

91.211 says that supplemental oxygen requirements are "above-type requirements for cabin pressure altitude", so if I'm in an unpressurized c182 at 12500' how do I determine my cabin pressure altitude?  

Ace Any FAA Written Test!
Actual FAA Questions / Free Lifetime Updates
The best explanations in the business
Fast, efficient study.
Pass Your Checkride With Confidence!
FAA Practical Test prep that reflects actual checkrides.
Any checkride: Airplane, Helicopter, Glider, etc.
Written and maintained by actual pilot examiners and master CFIs.
The World's Most Trusted eLogbook
Be Organized, Current, Professional, and Safe.
Highly customizable - for student pilots through pros.
Free Transition Service for users of other eLogs.
Our sincere thanks to pilots such as yourself who support AskACFI while helping themselves by using the awesome PC, Mac, iPhone/iPad, and Android aviation apps of our sponsors.

5 Answers



  1. Jeff Baum on Feb 23, 2021

    Indicated Altitude is the altitude shown on the altimeter for the set barometric pressure. The set barometric pressure IS the “altimeter setting” which you adjust in the Kollsman window.

    To find your Pressure Altitude, adjust the altimeter to 29.92. This is also used for most performance calculations as well. (Don’t forget to return it to the current “local altimeter” setting when you have the Pressure Altitude)

    BUT, since a 0.10 change in the altimeter setting equals only a 100 foot change, the difference between flying at 12,500 Indicated Altitude with a barometric setting of 30.12 (12,300 Pressure Altitude) or 12,500 with a barometric setting of 29.72 (12,700 Pressure Altitude) is kind of irrelevant to your Blood Oxygen Saturation Level (AKA – O2 SAT), which is what the regulation is all about.

    +1 Votes Thumb up 1 Votes Thumb down 0 Votes



  2. John D Collins on Feb 24, 2021

    I think Jeff already answered what you were looking for with your question, but I don’t understand your meaning of the quoted phrase: “above-type requirements for cabin pressure altitude”. The quoted phrase does not appear in 91.211 and I find it is confusing phraseology.

    0 Votes Thumb up 0 Votes Thumb down 0 Votes



  3. ben.mirsky on Feb 24, 2021

    is there an altitude at which an aircraft must be pressurized to operate above? or is the requirement for supplemental o2 only?

    0 Votes Thumb up 0 Votes Thumb down 0 Votes



  4. Jeff Baum on Feb 24, 2021

    There is no requirement to pressurize an aircraft, it’s all about oxygen requirements per Cabin Pressure Altitude. The requirements stated in 91.211 are listed as “Cabin Pressure Altitude”. If the aircraft is pressurized, the aircraft may be flying at Flight Level 370 (37,000 exterior Pressure Altitude) with a Cabin Pressure Altitude of 8,000, so no need to USE supplemental oxygen. Should you lose pressurization, the Cbin Pressure Altitude would start to rise to equalize with the exterior Pressure Altitude. NOW, the Cabin Pressure Altitude would be well above 12,500 pressure altitude and you would need to use supplemental oxygen.

    Unpressurized aircraft are just that… unpressurized. So, the exterior Pressure Altitude and the Cabin Pressure Altitude are the same. Under Part 91 regulation, once you climb your unpressurized 182 above 12,500 Pressure Altitude for more than 30 minutes, you are required to use supplemental oxygen. Should you climb above 14,000 PA you would be required to use supplemental oxygen at that time. If you really like to climb, and you exceed 15,000 PA you must provide oxygen to your passengers. The highest altitude which I have flown an unpressurized airplane is 25,000 sucking on oxygen.

    Now, part 135 and 121 operations have lower Cabin Pressure Altitude requirements.

    +1 Votes Thumb up 1 Votes Thumb down 0 Votes



  5. Jeff Baum on Feb 25, 2021

    Also, your original question referenced “above-type requirements…” That seems to be referring to where the regulation said “when above 12,500 Cabin Pressure Altitude” or “when above 15,000 Cabin Pressure Altitude”. If you remain AT a Cabin Pressure Altitude of 12,500 you would not be required to use supplemental oxygen. But if you are at 12,501 then you are above 12,500 and now fall under that part of the regulation.

    +1 Votes Thumb up 1 Votes Thumb down 0 Votes


The following terms have been auto-detected the question above and any answers or discussion provided. Click on a term to see its definition from the Dauntless Aviation JargonBuster Glossary.

Answer Question

Our sincere thanks to all who contribute constructively to this forum in answering flight training questions. If you are a flight instructor or represent a flight school / FBO offering flight instruction, you are welcome to include links to your site and related contact information as it pertains to offering local flight instruction in a specific geographic area. Additionally, direct links to FAA and related official government sources of information are welcome. However we thank you for your understanding that links to other sites or text that may be construed as explicit or implicit advertising of other business, sites, or goods/services are not permitted even if such links nominally are relevant to the question asked.