Unpressurized at altitude?

Saw this in another thread and got me wondering what things are like for civilian flying. Guess I could look it up regs but it seems easier to start a thread here In my world you gotta be on oxygen above 10k which means that high altitude drops tend to get done around 9k and I haven't noticed any after effects from that. I have been up to 18k unpressurized in an extraordinary circumstance.... how high do civilian pilots generally fly unpressurized?

 

FAA rules, here for jets, recips a little different Sec 121.327

Sec. 121.329 - Supplemental oxygen for sustenance: Turbine engine powered airplanes.

(a) General. When operating a turbine engine powered airplane, each certificate holder shall equip the airplane with sustaining oxygen and dispensing equipment for use as set forth in this section:

(1) The amount of oxygen provided must be at least the quantity necessary to comply with paragraphs (b) and (c) of this section.

(2) The amount of sustaining and first-aid oxygen required for a particular operation to comply with the rules in this part is determined on the basis of cabin pressure altitudes and flight duration, consistent with the operating procedures established for each operation and route.

(3) The requirements for airplanes with pressurized cabins are determined on the basis of cabin pressure altitude and the assumption that a cabin pressurization failure will occur at the altitude or point of flight that is most critical from the standpoint of oxygen need, and that after the failure the airplane will descend in accordance with the emergency procedures specified in the Airplane Flight Manual, without exceeding its operating limitations, to a flight altitude that will allow successful termination of the flight.

(4) Following the failure, the cabin pressure altitude is considered to be the same as the flight altitude unless it is shown that no probable failure of the cabin or pressurization equipment will result in a cabin pressure altitude equal to the flight altitude. Under those circumstances, the maximum cabin pressure altitude attained may be used as a basis for certification or determination of oxygen supply, or both.

(b) Crewmembers. Each certificate holder shall provide a supply of oxygen for crewmembers in accordance with the following:

(1) At cabin pressure altitudes above 10,000 feet, up to and including 12,000 feet, oxygen must be provided for and used by each member of the flight crew on flight deck duty and must be provided for other crewmembers for that part of the flight at those altitudes that is of more than 30 minutes duration.

(2) At cabin pressure altitudes above 12,000 feet, oxygen must be provided for, and used by, each member of the flight crew on flight deck duty, and must be provided for other crewmembers during the entire flight at those altitudes.

(3) When a flight crewmember is required to use oxygen, he must use it continuously except when necessary to remove the oxygen mask or other dispenser in connection with his regular duties. Standby crewmembers who are on call or are definitely going to have flight deck duty before completing the flight must be provided with an amount of supplemental oxygen equal to that provided for crewmembers on duty other than on flight duty. If a standby crewmember is not on call and will not be on flight deck duty during the remainder of the flight, he is considered to be a passenger for the purposes of supplemental oxygen requirements.

(c) Passengers. Each certificate holder shall provide a supply of oxygen for passengers in accordance with the following:

(1) For flights at cabin pressure altitudes above 10,000 feet, up to and including 14,000 feet, enough oxygen for that part of the flight at those altitudes that is of more than 30 minutes duration, for 10 percent of the passengers.

(2) For flights at cabin pressure altitudes above 14,000 feet, up to and including 15,000 feet, enough oxygen for that part of the flight at those altitudes for 30 percent of the passengers.

(3) For flights at cabin pressure altitudes above 15,000 feet, enough oxygen for each passenger carried during the entire flight at those altitudes.

 

and for recips:
Sec. 121.327 - Supplemental oxygen: Reciprocating engine powered airplanes.

(a) General. Except where supplemental oxygen is provided in accordance with §121.331, no person may operate an airplane unless supplemental oxygen is furnished and used as set forth in paragraphs (b) and (c) of this section. The amount of supplemental oxygen required for a particular operation is determined on the basis of flight altitudes and flight duration, consistent with the operation procedures established for each operation and route.

(b) Crewmembers. (1) At cabin pressure altitudes above 10,000 feet up to and including 12,000 feet, oxygen must be provided for, and used by, each member of the flight crew on flight deck duty, and must be provided for other crewmembers, for that part of the flight at those altitudes that is of more than 30 minutes duration.

(2) At cabin pressure altitudes above 12,000 feet, oxygen must be provided for, and used by, each member of the flight crew on flight deck duty, and must be provided for other crewmembers, during the entire flight time at those altitudes.

(3) When a flight crewmember is required to use oxygen, he must use it continuously, except when necessary to remove the oxygen mask or other dispenser in connection with his regular duties. Standby crewmembers who are on call or are definitely going to have flight deck duty before completing the flight must be provided with an amount of supplemental oxygen equal to that provided for crewmembers on duty other than on flight deck duty. If a standby crewmember is not on call and will not be on flight deck duty during the remainder of the flight, he is considered to be a passenger for the purposes of supplemental oxygen requirements.

(c) Passengers. Each certificate holder shall provide a supply of oxygen, approved for passenger safety, in accordance with the following:

(1) For flights of more than 30 minutes duration at cabin pressure altitudes above 8,000 feet up to and including 14,000 feet, enough oxygen for 30 minutes for 10 percent of the passengers.

(2) For flights at cabin pressure altitudes above 14,000 feet up to and including 15,000 feet, enough oxygen for that part of the flight at those altitudes for 30 percent of the passengers.

(3) For flights at cabin pressure altitudes above 15,000 feet, enough oxygen for each passenger carried during the entire flight at those altitudes.

(d) For the purposes of this subpart cabin pressure altitude means the pressure altitude corresponding with the pressure in the cabin of the airplane, and flight altitude means the altitude above sea level at which the airplane is operated. For airplanes without pressurized cabins, "cabin pressure altitude" and "flight altitude" mean the same thing.

 

In addition to the FARs posted below, when I was in the AF (ours), we required full time O2 above 10K.

Remember also, that these numbers are based on human performance tests, which can be extremely affected by other things.
We used to always say, if you were a regular smoker, you should consider your lungs at 8000 feet on the ground, and when you fly use O2 appropriately. Although it is less clear in the FAA written guidance, these cabin altitudes should be regarded as PRESSURE altitudes, and can be higher than you think depending on conditions.

Other factors such as time at altitude, hydration status, fatigue, chronic or acute illness and over the counter meds may also adversely affect aircrew performance when combined with low ambient oxygen concentrations and pressures.

That's enough to get started with some basics at this late hour. I know I am a weenie, but I never fly above 10K indicated without O2 for any length of time.

good AvChat topic for discussion.
best

Russ

 

Thanks for replying, Rob.
This is a good discussion of O2 requirements. Isn't it interesting that private and commercial O2 requirements differ, while the performance requirements are the same?

 

I used to cruise between 10 and 12K pretty regularly. My plane was equipped with an O2 tank and masks for all 4 seats; probably good for 3+ hours with all passengers on O2 at full flow as I recall. However, I also purchased a finger Pulse-Oximeter to measure blood O2 saturation to help monitor the flow settings. They were expensive back then (about $400), but I see some cheaper ones are around for $1-200 now (not sure how they compare accuracy wise, the one I had measured with good precision to hospital units). Within the saturation range in low 90's or higher, you were generally good. In the mid-80's you could notice tunnel vision, loss of color vision, sleepiness, etc.

 

While I think you probably could, the regs are written for the community as a whole, which means folks with reduced capacity for whatever reason. And as we said before, what you can tolerate one day, you may not be able to on another if there are intervening factors. Hypoxia is widely variable person to person and can be a little sneaky. There are hypoxia courses for private pilots utilizing altitude chambers or diluter masks to teach folks their individual symptoms of hypoxia - if you can do one, they are really quite good to learn one's limits

 

I tried to post this earlier today but screwed it up. I can speak from experience about the lack of oxygen. I failed to take a walkaround bottle with me when I went from the waist to the flight deck. I made it 90% of the way back. I woke up with the flight engineer in the tunnel to the nose position who had shoved a supply hose into my mouth to feed me 100% O2. he saw my head come up to the flight deck and then disappear and he figured out what the problem was. The metal fitting on the hose froze to my mouth so I got a bloody mouth, a chewing out, a headache, and a good lesson about how one can get hit with hypoxia and never know it.

 

How high? What kind of aircraft? Inquiring minds

 

B-24, 22000 ft. 1945, Langley Field, Va.

 

I failed to mention that I got hung up on the catwalk when my chute harness got tangled in the bomb racks. The good ol' catwalk. On my first flight in the B-24 the pilot waited until I was midway from the waist to the flight deck on the catwalk (which was about 10" wide) and pushed forward on the controls, leaving me scrambling for a grip in mid air for a LOOONg time. Sometimes when you kicked the bombay doors they could open and landing on them in this case was not wise if you weren't wearing your chute.

 

I have had the.... for lack of a better word..... pleasure of being able to partake in an altitude chamber ride. We went up to a equivalent pressure of 25,000 ft and proceded to take off our oxygen masks, I had to take one of those toys that todlers have that are a cube with shapes cut into it and corosponding shapes to put through the holes. (like this http://www.discountattic.com/toysandgames/34817-ToddlerSortingToy.jpg) Well long story short after about 3 minutes that was an extremely difficult task to complete. I even got to the point where I carried on a conversation with someone else in the chamber that I dont remeber at all. Scary stuff. The point behind it was to be able to recognize the effects of hypoxia. Im glad i got to do it cause now i know what to look out for and its somthing I make sure to encorage my students to do as well.

 

Back when I was in the AF, I got high altitude training in preparation for a back seat ride in a F-15D. We did our training at Offutt AFB in Nebraska. We did rapid decompression training to get use to doning masks and turning on O2 flow quickly. We also went up to about 30k feet in the chamber and then removed our masks (on the buddy system) and were asked to do simple math, color vision and coordination tests. I lasted probably about 1 minute without the mask before my partner had to lift me up (I slumped over) and get my mask on. Very embarassing, but a great lesson in understanding how my body reacted to oxygen deprivation and I got my high altitude endorsement. Later in my career when I worked for Cessna designing ECS and presurization systems on the Citation line, I had a healthy respect for the importance of those systems.