The aircraft fuselage is pressurized to a "differential pressure". At 51,000 feet, outside air is about 1.6PSI. So the cabin would have a total of 12.6 PSI absolute. Which is about the same as a 4200 foot elevation.
Depressurization incidents..
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Cujet,
So if sea level atmospheric pressure is 14.7, and at 51,000 ft. it is 1.6, that's about 9 times less. I'm curious, with so much of the atmosphere underneath you, what does the airplane handle like at that altitude?
Is it much less responsive and "mushy"? And is your bank angle more severely limited? I just wondered how the airplane hand flies in that very rarefied air?
So if sea level atmospheric pressure is 14.7, and at 51,000 ft. it is 1.6, that's about 9 times less. I'm curious, with so much of the atmosphere underneath you, what does the airplane handle like at that altitude?
Is it much less responsive and "mushy"? And is your bank angle more severely limited? I just wondered how the airplane hand flies in that very rarefied air?
Cujet, you mention once mask is on with 100% selected, you learned to exhale then inhale deeply. What made you choose this specific breath pattern? Genuinely curious, as I have never seen nor heard any advice on how to breathe once the mask is on and doing it's thing. Thanks in advance.
Some civilian aircraft are certified to 51,000'. If a rapid decompression occurs at 51,000' your blood boils, all gases come out of solution.
The highest I ever commanded an aircraft too was 45,000'. We practiced "pressure breathing" and emergency decents in the sim annually.
The highest I ever commanded an aircraft too was 45,000'. We practiced "pressure breathing" and emergency decents in the sim annually.
I thought that was 62,000 - 63,000 ft? Also known as, "Armstrong's Line".
Armstrong limit - Wikipedia
"The U.S. Standard Atmospheric model sets the Armstrong pressure at an altitude of 63,000 feet (19,202 m)."
The air is coming out of the lungs, no matter what. There is no choice with that. Best to not try to hold it in, and instead work to push it out, then inhale deeply. In my mind it's a time saver, as you get fresh O2 in sooner, than trying to hold any remaining breath.
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The Gulfstream wing is very large. So it performs well at altitude. Gulfstream used to demonstrate 45 degree turns at FL510. Umm, I don't think this is a great idea, as AOA is well into the yellow when doing so. Always on autopilot at FL510.
And before someone accuses me of lens distortion, the sun shade is square...
IIRC Pilot mask in the jets I flew had mask settings of a) on demand like scuba diving regulator , and b) pressure breathing were the 02 is FORCED into your lungs. Takes practice and its difficult to communicate with crew and atc.
Thanks for the further info. Sound logic in there, will add it to my thought process and hope to never need it. Appreciate it.
In the early 80s I did a high altitude course with a chamber ride at Brooks AFB. WOW
All that I flew handled poorly/mushy at 40+. Always had it on autopilot. I never horsed it around at altitude, but sometimes turbulence horses you around and its not fun.
Some Learjet models (large tip tanks) required 2 operational yaw dampeners for dispatch.
Cujet,
I could look at those pictures from 51,000 ft. all day long. It has to do something to you being up there, knowing everyone, along with all the B.S. in the world is 9.6 miles beneath you.
I could look at those pictures from 51,000 ft. all day long. It has to do something to you being up there, knowing everyone, along with all the B.S. in the world is 9.6 miles beneath you.
From an ATC perspective, my answer is no: Rapid decompression incidents are VERY few and far between. We run about 5000 flights daily though our airspace and I generally work only 3-4 depressurizations a year. Almost all are GA. Honestly can’t remember the last time a commercial airliner depressurized. The more typical events tend to be either an aircraft that just came out of MX that won’t pressurize on climb-out or a high performance GA single or twin that has a precautionary warning. I’ve only had the misfortune of working 2 hypoxia events in 18 years. It’s gut wrenching.
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Good to know but I have a question please.
If we need to perform an emergency descent ( loss of pressurization or thick smoke in the plane…need to get down to depressurize and open ram air to ventilate ) , our airline policy is to advise ATC ( mayday ) and rely on them for terrain clearance ( charts with minimum safe altitudes is only if ATC is unable ) while we leave cruise altitude ASAP down to 10,000 if possible.
As pilots, we all understand minimum radar vectoring altitudes ( normally down low , close to the airport ) but how do you know what the safe altitude is when a flight performs an emergency descent and high terrain is present ( folks, pilots know, we have charts, but )?
The high level controller doesn’t think about terrain and that’s who we would in contact with and not on radar vectors in cruise.
Normally pilots are responsible for terrain clearance unless on radar vectors only ( some airline pilots still don’t grasp or remember that which has caused a few GPWS issues when coming in for approaches and I will leave it at that ) so how do you guarantee flights the lowest safe altitude in high terrain in an emergency like loss of cabin pressure?
If a was “ on coarse “ ( not on radar vectors ) and asked for the lowest ATC safe altitude over the Rockies , how does ATC handle that?
e.g YUL - LAX and lose pressurization 50 miles west of DEN.
If I am on the company flight plan route , it has a MORA ( 5 nm either side of track ) that safely allows us to descend to a specified altitude ( 2000 feet obstacle clearance over mountains , 1000 everywhere else ) but if we are flying off flight plan ( ATC request or we request direct to some fix ) , our charts say the lowest I can go is 17,000 feet when about 50 miles west of Denver.
The Airbus has around 13 minutes oxygen minimum ( when NOT on 100% ….therefore diluted ) and I need to get lower than 18,000 after 12 minutes from the time the emergency descent was initiated ( so after about 75 - 100 miles ) and down to 13,000 within 13 minutes.
How would ATC get us down as low as possible in that situation?
I am asking for others on BITOG who might be curious.
As a pilot, I know how to get down but people on this site might like to hear how ATC would handle a flight in a situation like that.
Thanks
Ok so background, I’m speaking purely in center terms.
Typically, each sector you fly though is part of a cluster of high & low sectors that make up geographical areas in each center. Ie; the center I work in has 6 areas, with a mix of 6-8 high and low sectors covering that specific area. Generally speaking, the controller you are talking to has an intimate knowledge of both the high and low airspace for that geographic area. I say all that to set up that we have specific display maps for high or low airspace. On all low maps, the entire map has a selectable MIA coverage overlay. There isn’t any part of the entire center that I can’t call up the MIA immediately regardless of the stratum I’m working.
So case in point, if you’re with me at FL390 and declare an emergency for depressurization (I already know what the emergency is because I can hear you with your mask on), I’m going work you all the way down to 10, through the low altitude controllers airspace and traffic, and get you stabilized before handing you off to the low. Only rare circumstances dictate that I have to hand you off to the low altitude controller in the middle of your emergency descent. We’re moving everyone out of your way and we aren’t planning on you stopping anywhere before 10. I’ve never seen an emergency descent to 10 take more than 10 minutes. My highest MIA is 4600 so I never even have to pull up the low map.
In regards to mountainous terrain, however, obviously you’re only getting the lowest MIA available. Our MIA charts are 1k above nearest obstacles, 2k in mountains just as yours are. Likely you will be offered a vector to a lower MIA if you’re stuck over higher terrain, but all that information is right at the controllers fingertips.
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Very interesting and thanks for taking the time writing a detailed explanation.
As expected , ATC is very familiar with the airspace they are assigned to ( terrain and airports ). I tell pilots that and to use them as a resource when busy dealing with emergencies , especially time critical ones ( cargo smoke …..divert……”need 7000 runway, ILS preferred” versus pilots distracting themselves trying to fly and look up )
I tell pilots flying non radar to the Caribbean ( “ ARINC “ ) to always ( every position report ) think about the next closest suitable airport in the event of a time critical emergency in particular ( smoke in cabin , cargo smoke warning ) because we are not talking directly to ATC ( plus using HF ) whereas we are when overflying the u.s.
If terrain is not an issue, we would be down to 10,000 very quick. I was just mentioning the worst case if over the Rockies.
39,000 to 10,000 ( if no structural damage ) would take around 5 minutes and cover 40 miles.
Yep, you would be able to tell if we have our masks on through the radio.
I heard some major u.s airline on oxygen saying they had a pressurization problem and needed lower then went full blown emergency descent ( around North Carolina on our way to Florida ).
Nice talking with you and glad to have an air traffic controller on BITOG,
Airbus Captain with major airline ( line pilot by choice but do unofficial training and upgrade mentoring ).
“ unofficial” as in anytime I fly with new pilots or new to the Airbus.
Training pilots are not paid enough extra as far as I am concerned ( my airline anyways ).
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