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jhooper
Topic Author
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Cabin Depressurization

Mon Nov 17, 2003 3:58 pm

Why is it that useful consciousness is merely a few seconds at, say, FL550, in the event of cabin depressurization? Just because oxygen can't get to the body, why can't one hold their breath for a few minutes like they could at sea level?
Last year 1,944 New Yorkers saw something and said something.
 
pilotpip
Posts: 2844
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RE: Cabin Depressurization

Mon Nov 17, 2003 4:44 pm

According to "Human Factors in Multi-Crew Flight Operations" by Harry and Linda Orlady the Time of Useful Consiousness(TUC) at FL300 varies from 30 to 74 seconds based on the individual. I have a graph somewhere but I can't find it. I know it drops off much faster as altitude increases. Above FL410 pilots are required to wear an oxygen mask at all times. There are some exceptions to this rule, such as the Concorde and some bizjets. All aircraft that fly at high altitude require quick donning masks that can be put on with one hand in 5 seconds or less.

I really don't think your holding breath thing would work. Take the Payne Stewart crash for instance. Fighter jets noticed the inside of the windows were frosted over. This was most likely caused by a rapid decompression. The pilots obviously didn't have time to recognize this and put on their masks. All occupants went unconsious and the aircraft ran on autopilot until it exhausted it's fuel. Most aircraft have a system that will deploy the pax oxygen automatically above cabin altitudes of about 13,000 feet. This will also trigger all kinds of anunciators and warnings. Also, in a gradual decompression your motor skills are already degraded by hypoxia and a lack of oxygen but may not be recognized. If you aren't getting enough to begin with I'm sure holding your breath won't keep you consious that long. I'll try it next semester when my class goes to Oklahoma and visits the FAA high altitude chamber.
DMI
 
liamksa
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RE: Cabin Depressurization

Mon Nov 17, 2003 5:37 pm

The differential pressure between 8000' (typical cabin) and FL550 would be WAY too big to hold your breath. The 1st thing a rapid decompression will cause is you to forcibly exhale your breath (maybe closely followed by your bowels).
 
Guest

RE: Cabin Depressurization

Tue Nov 18, 2003 12:05 am

Pilotpip...
I'm going to take another opinion on a few items in your last post.

"...Above FL410 pilots are required to wear an oxygen mask at all times. There are some exceptions to this rule, such as the Concorde and some bizjets. All aircraft that fly at high altitude require quick donning masks that can be put on with one hand in 5 seconds or less..."

This statement is partially true. In the US (I have no idea about the regulations of other countries.), the regulations on wearing of 02 masks kick in at various altitudes - depending upon what section of the FARs you are operating under, Part 91, 135, 121, etc. For commercial operations (Parts 135 & 121) the requirement to use O2 masks kicks in at 25,000' for non-commercial operations that altitude is increased to 35,000'. IF the aircraft is equipped with quick donning masks, then you are give some options as to their wearing and use. As far as I know, there are NO exceptions to the rules (again, the Concorde wasn't a US registered aircraft) so no bizjets are exempted from the regulations. If you've ever been in a cockpit at FL370 or higher, don't be surprised if the crew is taking certain "liberties" with the wearing of their masks. Those regulations are probably the most frequently "overlooked and ignored" regulations we have.

"...Take the Payne Stewart crash for instance. Fighter jets noticed the inside of the windows were frosted over. This was most likely caused by a rapid decompression. The pilots obviously didn't have time to recognize this and put on their masks. All occupants went unconscious and the aircraft ran on autopilot until it exhausted it's fuel. Most aircraft have a system that will deploy the pax oxygen automatically above cabin altitudes of about 13,000 feet..."

First of all, the official explanation of the Payne Stewart crash is still listed as UNKNOWN. That being said, I'm typed in the Lear series and have nearly 3,000 hours PIC in the Lear 35 and I have always been bothered by certain points that were brought out in the investigation.

A couple of months ago, I returned from my 6-month Gulfstream G100 recurrent training at FlightSafety. During our discussion on pressurization systems we had the obligatory discussion on the Payne Stewart accident. The systems instructor brought up some new information that sheds new light on what may have happened.

The thing that always puzzled me about the accident was that, in my opinion, they overlooked one item - the Lear 35, while only certified to FL450 has the same pressurization system that is certified to FL510 in their other airplanes. The Lear's pressurization system has automatic cabin altitude limiters designed into it that make it impossible for the cabin altitude to go above 14,000' or so (Not 13,000' as you mentioned in your post.) in a structurally sound airplane. Remember the reports? The F-16 chase planes saw no evidence of airframe damage - only frosted up windows. 14,000' is hardly an altitude that will bring on terminal hypoxia.

The fact that the windows were frosted means nothing - only that the cabin temperature control hadn't been turned up. At low altitudes, the cabin gets pretty warm because of the pressurized air. It's normal to have the heat turned way down and or the airconditioner turned on to compensate. If you've ever spent much time in a Lear at altitude you'll know that they do have a tendency to frost the windows - especially if the heat's off and you've got a bunch of people in the cabin. No big surprise there.

This didn't make any sense to me until the FlightSafety instructor mentioned that they have recently found witnesses who mentioned that the passengers had loaded some frozen fish in the baggage compartment in the cabin behind the rear bench seat. There are also witnesses who say that there were several pounds of dry ice packed with the fish.

That changes everything. Dry ice is a VERY dangerous commodity to carry in the passenger compartment. It will readily displace the oxygen in the space and easily explains the accident. It wouldn't be the first fatal aircraft accident involving dry ice.

It remains to be seen if this new information will be confirmed and if it will have any effect on the official report.

As to why holding your breath won't work? It has to do with the oxygen partial pressure. At those altitudes, you just can't get the oxygen, at the molecular level, to transfer through the cell wall into the red blood cell.

I'd like to make a suggestion for all of you guys who are flying high performance aircraft (or hope to someday). Get yourselves scheduled for a ride in an altitude chamber. The cost is VERY reasonable and you'll walk away with a new found respect for your physical limitations. There are several chambers located around the country, I'd just give your local FSDO a call and get them to point you in the right direction.

Jetguy
 
Guest

RE: Cabin Depressurization

Tue Nov 18, 2003 12:20 am

In certain countries, pilot crewmembers operating aircraft certificated for operations above FL250 are required to have altitude chamber training. While it is not a regulation (yet) in the USA, I would recommend such training as a must for anyone flying at high altitudes. One of the good things you get in the Air Force or Navy pilot training... Argentina requires that training.
xxx
Happy contrails  Smile
(s) Skipper
 
pilotpip
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RE: Cabin Depressurization

Tue Nov 18, 2003 9:37 am

Jetguy,

Thanks for the insight. I'm going down to Monrey next semester to do the altitude chamber. The altitude that I gave for the warnings or pax O2 to come down was just what the majority of aircraft I've learned about. Unfortunately it's almost all part 121 ops with bigger aircraft. Not the way I plan on going in my career.

My only physical experience with Lears has been running back and forth with a fuel hose keeping the wings balanced. If all goes as planned they will be the first jet I'm flying. What I've been reading doesn't give the whole picture becuase it's mostly introductory or intermediate books on the topic. The authors are too busy explaining what the system does in all aircraft as opposed to how it works in a specific machine. That being said, do these rules apply to pressurized cabins as well? Does that mean that all crews flying above FL250 should be wearing O2?

I had the opportunity to check out the cockpit of a G100, a crew that was at my FBO a few months back was nice enough to show me the toys, very nice. Looks like a fun aircraft to fly.
DMI
 
Guest

RE: Cabin Depressurization

Tue Nov 18, 2003 10:33 am

Pilotpip...
Looking back on my post, I did make one error. You were correct about the passenger's O2 masks deploying at a cabin altitude of 13,000'. What I was referring to was the Cabin Altitude Limiter which closes the outflow valves at 14,000'. It's this Cabin Altitude Limiter which, in my opinion, makes the dry ice theory the only plausible explanation. As long as you have a structurally intact aircraft, the highest the cabin can ever get is 14,000 feet. Now if they had blown a door or a window that would indeed do it - but the chase pilots noted no visible damage.

As far as the various O2 regulations go, the US FARs apply to any civilian US registered aircraft be it turbojet, turboprop, or piston-powered, single or multi-engine. As far as who has to wear what and when, I'll let you read it for yourself.

For non-commercial (Part 91) operations:

§ 91.211 Supplemental oxygen.

(a) General. No person may operate a civil aircraft of U.S. registry --

(1) At cabin pressure altitudes above 12,500 feet (MSL) up to and including 14,000 feet (MSL) unless the required minimum flight crew is provided with and uses supplemental oxygen for that part of the flight at those altitudes that is of more than 30 minutes duration;

(2) At cabin pressure altitudes above 14,000 feet (MSL) unless the required minimum flight crew is provided with and uses supplemental oxygen during the entire flight time at those altitudes; and

(3) At cabin pressure altitudes above 15,000 feet (MSL) unless each occupant of the aircraft is provided with supplemental oxygen.

(b) Pressurized cabin aircraft. (1) No person may operate a civil aircraft of U.S. registry with a pressurized cabin --

(i) At flight altitudes above flight level 250 unless at least a 10-minute supply of supplemental oxygen, in addition to any oxygen required to satisfy paragraph (a) of this section, is available for each occupant of the aircraft for use in the event that a descent is necessitated by loss of cabin pressurization; and

(ii) At flight altitudes above flight level 350 unless one pilot at the controls of the airplane is wearing and using an oxygen mask that is secured and sealed and that either supplies oxygen at all times or automatically supplies oxygen whenever the cabin pressure altitude of the airplane exceeds 14,000 feet (MSL), except that the one pilot need not wear and use an oxygen mask while at or below flight level 410 if there are two pilots at the controls and each pilot has a quick-donning type of oxygen mask that can be placed on the face with one hand from the ready position within 5 seconds, supplying oxygen and properly secured and sealed.

(2) Notwithstanding paragraph (b)(1)(ii) of this section, if for any reason at any time it is necessary for one pilot to leave the controls of the aircraft when operating at flight altitudes above flight level 350, the remaining pilot at the controls shall put on and use an oxygen mask until the other pilot has returned to that crewmember's station.


The following applies specifically to commercial air-taxi (Part 135) operators, but the regulations for airline operations (Part 121) are similar:

§ 135.89 Pilot requirements: Use of oxygen.

(a) Unpressurized aircraft. Each pilot of an unpressurized aircraft shall use oxygen continuously when flying --

(1) At altitudes above 10,000 feet through 12,000 feet MSL for that part of the flight at those altitudes that is of more than 30 minutes duration; and

(2) Above 12,000 feet MSL.

(b) Pressurized aircraft. (1) Whenever a pressurized aircraft is operated with the cabin pressure altitude more than 10,000 feet MSL, each pilot shall comply with paragraph (a) of this section.

(2) Whenever a pressurized aircraft is operated at altitudes above 25,000 feet through 35,000 feet MSL, unless each pilot has an approved quick-donning type oxygen mask --

(i) At least one pilot at the controls shall wear, secured and sealed, an oxygen mask that either supplies oxygen at all times or automatically supplies oxygen whenever the cabin pressure altitude exceeds 12,000 feet MSL; and

(ii) During that flight, each other pilot on flight deck duty shall have an oxygen mask, connected to an oxygen supply, located so as to allow immediate placing of the mask on the pilot's face sealed and secured for use.

(3) Whenever a pressurized aircraft is operated at altitudes above 35,000 feet MSL, at least one pilot at the controls shall wear, secured and sealed, an oxygen mask required by paragraph (b)(2)(i) of this section.

(4) If one pilot leaves a pilot duty station of an aircraft when operating at altitudes above 25,000 feet MSL, the remaining pilot at the controls shall put on and use an approved oxygen mask until the other pilot returns to the pilot duty station of the aircraft.


The G100 is a lot of fun to fly. It's about the only airplane that I've flown that actually has "enough" power most of the time. Airplanes are just like any other piece of equipment - you've never ridden in a car, motorcycle, boat, snowmobile or jet ski that had enough power. Airplanes are the same way.

Jetguy




 
airplay
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RE: Cabin Depressurization

Tue Nov 18, 2003 12:03 pm

Forget all that.....

The reason holding your breath won't work is that the special cells in your lungs require a minimum pressure in the lungs in order to have oxygen transfered to the blood stream.

Once the pressure in the air you breath falls below this level, you will no longer absorb the oxygen in your lungs no matter how long you hold it in.

This can be overcome using a pressure oxygen delivery system like some high flying fighter pilots use, but the masks used in airliners are the demand type that don't force the air into your lungs.

Aircraft that fly at high altitudes must be certified to higher standards with respect to the probability of loss of pressure. If an airplane has a massive decompression above 42,000 feet, there is a very good chance everyone will die.
 
pilotpip
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RE: Cabin Depressurization

Tue Nov 18, 2003 1:20 pm

Jetguy,

I'm flying the Seminole right now. 180 hp gives this thing a single engine service ceiling of about 2500 feet in ISA conditions. You wanna talk about power?

Yeah, I knew about the supplimental O2 requirements above 10,000. Those almost apply to me. But living in the midwest there is no real reason to get that high. It's when you get into the turbine world that I'm not too proficient. I knew that most bizjet operators went as high as they could to go direct to the destination and be more efficent. When I read that at first I thought, there was no way that those guys wear that mask up at FL450.

The thing that impressed me most with the G100 was the FADEC system. The f/o thought the digital link was the neatest thing. He seemed to marvel at the fact that the throttles move back and forth with no resistance.
DMI
 
Guest

RE: Cabin Depressurization

Tue Nov 18, 2003 2:23 pm

Pilotpip...
Actually, the G100 uses DEECs (Digital Electronic Engine Controls) not FADECs (Full Authority Engine Controls). You don't get into the FADECs until the G200. The power levers are in those aircraft are basically just rheostats. The takeoff, climb, and cruise settings are just "flat spots" on the rheostat windings. You still have to check the charts to get the proper N1 settings for takeoff, climb, and cruise. The DEEC's computer is smart enough to get you in the ball park and you'd probably never hurt the engines is you never used the charts; but FADEC it isn't. The FADEC in the G200 is really awesome. It makes turbine engine management "silly simple".

You're right about the altitude profiles that we typically use. The rule of thumb is to climb as fast as you can, as high as you can, stay at altitude as long as you can, then descend as fast as you can. The objective is to maximize your time at altitude. As far as altitude selection goes, in a perfect world (No ATC or traffic conflicts.) we plan on climbing to an altitude equal to twice the distance not to exceed FL430. For example, on a 150 nm leg, we could climb to either FL290 or FL310 depending upon the direction of flight (2 X 150 = 300). The time to climb would be approximately 10 minutes. We can climb into the 40's on most trips over 200 miles or so. On these short legs, we really don't spend much, if any, time in level cruise - by the time we get to altitude it's time to start our descent. We use computers for our flight planning and it really is the most efficient way to fly the jets. However, with the turbofan engines, altitude selection isn't as critical as it was on aircraft with turbojets. (For example, 20 Series Lears burn as much fuel idling on the ramp as they do in cruise flight at FL410. On those airplanes it is ABSOLUTELY critical that you get into the low to mid 40's ASAP and don't let them start you down too early.) With turbofans, we can pretty much take any FL offered without having to sweat the fuel. I got my gray hair in the Lears, not the G100 and 200.

Airplay restated what I said in my earlier post. Holding your breath won't work. The oxygen partial pressure is too low to allow transfer into the red blood cells.

Oh well, time to go walk the dog. Later.

Jetguy

[Edited 2003-11-18 06:26:08]
 
AAR90
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RE: Cabin Depressurization

Tue Nov 18, 2003 3:54 pm

The reason holding your breath won't work is that the special cells in your lungs require a minimum pressure in the lungs in order to have oxygen transfered to the blood stream.

As Jetguy said: "partial pressure."  Wink/being sarcastic

This can be overcome using a pressure oxygen delivery system like some high flying fighter pilots use, but the masks used in airliners are the demand type that don't force the air into your lungs.

Airliner cockpit quick-donning masks have an "emergency" mode which switches the mask from a "demand" mode to a "positive pressure" mode.

If an airplane has a massive decompression above 42,000 feet, there is a very good chance everyone will die.

Not likely; however, non-cockpit occupant survival would depend upon aircraft structural integrity and flight crew abilities.
*NO CARRIER* -- A Naval Aviator's worst nightmare!
 
airplay
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RE: Cabin Depressurization

Wed Nov 19, 2003 3:38 am

Airliner cockpit quick-donning masks have an "emergency" mode which switches the mask from a "demand" mode to a "positive pressure" mode.


The quick donning masks "emergency" mode simply bypasses the demand valve and pisses oxygen directly into the mask. Although the result is a slight increase in oxygen mask pressure, it still doesn't meet the requirments of pressure delivery masks nor is it the intent. Pressure delivery masks (and yes I know they call the airline style "pressure-demand" masks) are very specialized pieces of gear that you need some training to use.

Not likely; however, non-cockpit occupant survival would depend upon aircraft structural integrity and flight crew abilities.

Not likely? According to the FAA/JAA/CAA etc, massive decompression in an aircraft approved for high altitude operations, is considered a catastrophic failure. Catastrophic failures are defined as those that prevent continued flight and landing. The acceptable probability of catastrophic failures is 1 in 1 billion flight hours.

Contrary to what you might believe, the aviation authorities consider these high altitude decompressions unrecoverable and quite "likely" to kill everyone on the airplane. Flight crew, pax, animals in the hold...everyone.

Even in a 10,000 FPM dive, your 51,000 foot altitude will only be at 410 after a minute.

 
vc10
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RE: Cabin Depressurization

Wed Nov 19, 2003 4:18 am

The only airliner which had pressure breathing for the crew was I believe Concorde, and the flight deck crew had to practice it's use every so often with a doctor present in case things went wrong. Believe me you would know if you have ever used a pressure breathing system, because it is hard work and very tiring. You have to think about every breath you take, and when you were going to try and say something

regards little vc10
 
dl1011
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RE: Cabin Depressurization

Wed Nov 19, 2003 4:47 am

Interesting material in this thread.

Wasn't there some speculation that the pneumatic and/or pressurization systems had some maintenance performed and some parts replaced before the accident? I seem to recall reading something along that track. Or was that just "informed" media hype?
 
chdmcmanus
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RE: Cabin Depressurization

Wed Nov 19, 2003 4:48 am

As far the concord goes, 56000 ft is the "Armstrong line" where water boils at ambient pressure, thus any ERD above, and all the pressure demand masks in the world wont help you unless you are in a pressure suit, or your internal fluids will boil.

In my previous airframe we occasionally flew high altitude airdrop. As high altitude I mean 9999-42000 ft. The highest altitude I have flown, unpressurized, is 35,000 feet. Jetguy and Airplay both did an outstanding job of illustrating the requirements. Airplay is correct about the quick-don masks, they can work as pressure-demand or diluter-demand, but they are designed for emergency use. When we flew above 10,000 we used a helmet mounted, face formed O2 mask. VC-10 is also right on the money with pressure breathing. Not only is it difficult to function with the myriad of hoses and connections, when you are in pressure mode, you must "reverse" breathe. That means instead of inhaling and relaxing to exhale, you relax to inhale, (the pressure does it for you) and force exhale. It really makes talking difficult. The other aspect that has not been discussed yet is Nitrogen Narcosis, and the bends. Whenever we fly above 10k unpressurized, we have a pre-breathing requirement depending on the altitude. At 35k it was almost 2 hours on pressure oxygen prior to takeoff, and if you broke mask seal, you started over. This super-saturated the blood with O2 to prevent those tiny bubbles and hypoxic reactions we hate so much.

The only advise I have on the subject is this, B747Skipper said it, Jetguy said it, and I am sure many others have too; IF YOU GET THE OPPORTUNITY, GO TO AN ALTITUDE CHAMBER!!!! I go every 5 years (it used to be 3 for the DoD but it recently changed) each time we are required to make 3 ascends, a Hypoxia check (you learn your particular symptoms in an effort to prevent) and you do an ERD. The ERD is from SL to 24k I believe, and it is an eye opener! BANG white fog, lungs screaming for air, and a screaming instructor, mask off hook, throw open, over the head, gang load the regulator try to sit upright, you look stupid hunched over! It only takes about 5-7 seconds for the whole thing but it feels like hours!
"Never trust a clean Crew Chief"
 
zak
Posts: 1926
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RE: Cabin Depressurization

Wed Nov 19, 2003 6:25 am

dont forget the dangers of tailstrike depressurization where the tail strikes a cloud and all hope is lost :/ (couldnt resist)
10=2
 
airplay
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RE: Cabin Depressurization

Wed Nov 19, 2003 6:35 am

This could happen if the oxygen tanks were filled with nitrous oxide instead of oxygen and both pilots donned the masks during the takeoff roll and subsequent over-rotation.

 Smile

And remember, the leading cause of tailstrikes are a result of the tail of the aircraft effectively "striking" the ground. And following the tailstrike, you need a tailstrike inspection carried out by tailstrike maintenance personnel tailstrike tailstrike tailstrike tailst......

 
Bellerophon
Posts: 535
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Cabin Depressurization

Wed Nov 19, 2003 8:47 am

Chdmcmanus

An interesting post, and I take my hat off to those whose job requires them to jump out of serviceable aircraft at 35,000 ft, something you would never persuade me to do!

You mentioned the Armstrong Line, and the pressurized aircraft we have today are a direct result of the pioneering work done by Dr Harry Armstrong at Wright Field in the late 1930’s.

It was there he discovered, amongst other things, that at 63,000 feet pressure altitude, blood will boil at body temperature, an altitude limit know to this day as the Armstrong Line.

Those who would like to know more about Dr Armstrong can try this link:

http://www.nationalaviation.org/museum_enshrinee.asp?eraid=4&enshrineeid=329

Some years ago I listened to a talk from a pilot who has flown considerably faster and higher than I, and the details and specifications of the pressure suit he wore at work were fascinating.

I hadn’t realised that his helmet was pressurised to sea level with 100% 02, whilst the rest of the suit was only pressurised to around 30,000 feet.

Regards

Bellerophon
 
AAR90
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RE: Cabin Depressurization

Thu Nov 20, 2003 1:08 am

...it still doesn't meet the requirments of pressure delivery masks nor is it the intent.

Never said it met any requirements nor did I say it was ever intended to.

Pressure delivery masks (and yes I know they call the airline style "pressure-demand" masks) are very specialized pieces of gear that you need some training to use.

Been there, done that, having "passed the gas" and "touched the bottom" many many times. It is neither hard work nor is it tiring... once you learn how to do it properly. The hardest part for me was probably the simpliest... breathing upside-down underwater.

Not likely? According to the FAA/JAA/CAA etc, massive decompression in an aircraft approved for high altitude operations, is considered a catastrophic failure. Catastrophic failures are defined as those that prevent continued flight and landing. The acceptable probability of catastrophic failures is 1 in 1 billion flight hours.

Now adding definitions to the discussion? Is the "catastrophic failure" described above not a structural failure? Is it not possible to have a "massive decompression" without structural failure?

Contrary to what you might believe, the aviation authorities consider these high altitude decompressions unrecoverable and quite "likely" to kill everyone on the airplane. Flight crew, pax, animals in the hold...everyone.

I guess that depends on what you are willing to accept for your definitions. I've experienced 4 "massive" decompressions (less than 3 seconds to reach atmospheric pressure) while cruising at/above FL420. Two in airliners and two in F-14's. Nobody died in any of those incidents. Since there was no "catastrophic failure" of the airframe I guess that means they didn't meet the legal definition of "massive decompression"???

Even in a 10,000 FPM dive, your 51,000 foot altitude will only be at 410 after a minute.

So now the ...massive decompression above 42,000 feet scenario magically becomes your 51,000 foot altitudeInsane
*NO CARRIER* -- A Naval Aviator's worst nightmare!
 
airplay
Posts: 3369
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RE: Cabin Depressurization

Mon Nov 24, 2003 1:29 am

OK...

Never said it met any requirements nor did I say it was ever intended to.

You stated:

Airliner cockpit quick-donning masks have an "emergency" mode which switches the mask from a "demand" mode to a "positive pressure" mode.


Doesn't that imply that this "positive pressure mode" will mitigate the lack of cabin pressure so that the crew can continue to breath? Its an incorrect statement and the reason is that the masks really don't do what you say they do.

Been there, done that, having "passed the gas" and "touched the bottom" many many times. It is neither hard work nor is it tiring... once you learn how to do it properly. The hardest part for me was probably the simpliest... breathing upside-down underwater.

If you "been there done that" then wouldn't you know that airliners aren't equipped with this type of mask?

Now adding definitions to the discussion? Is the "catastrophic failure" described above not a structural failure? Is it not possible to have a "massive decompression" without structural failure?

I see you're not a certification specialist. Aircraft are designed to meet the relevant airworthiness standards. Several of these standards use the term "catastrophic" but not any of the structural standards. Stuctures are designed to have a saftey margin above and beyond the flight loads. Yes. It is entirely possible to have massive decompression without a structural failure. And thats exactly what I was talking about. If you were a certification specialist you would know that. Structural massive decompression is typically caused by improper maintenance or damage to the airframe caused by impact or an explosion etc... This isn't considered a "failure".

I guess that depends on what you are willing to accept for your definitions. I've experienced 4 "massive" decompressions (less than 3 seconds to reach atmospheric pressure) while cruising at/above FL420. Two in airliners and two in F-14's. Nobody died in any of those incidents. Since there was no "catastrophic failure" of the airframe I guess that means they didn't meet the legal definition of "massive decompression"???

Thats pretty funny....first of all in an F-14 you would be wearing a pressure mask and a G suit. So why bring that into the discussion. As far as the airliners go, the standards for high altitude flight apply to aircraft above 42,000 feet (in the US) and above 41,000 feet (in Canada). If you are at 41K or 42K you are at the lower limit of recovery. Don't ask me why Canada and the US differ here...I wasn't involved in the development of the standards.

Having said that, I'm fairly sure you're lying about the massive decompressions on the airliners. The vast majority of career airline pilots don't experience massive decompressions in aircraft above 410/420. So why should I beleive that a "business owner and LL umpire" has experienced four? Furthermore, a quick review of SDRs and accident/incident reports in the last 33 years shows all recorded instances of rapid decompression in the US occured on aircraft well below 410/420. And all on aircraft not certified above 410/420.

How many times have you been hit by lightning?

So now the ...massive decompression above 42,000 feet scenario magically becomes your 51,000 foot altitude.

Ummm...no. If you read the discussion above, there is some mention of some aircraft being certified to 510. I was merely using that as an exteme example. Of course, you need only about 10 seconds at 410/420 before people start dying. How fast do you think you can safely descend in an airliner from say 450 to 410? Even at 10,000 fpm you're talking just under 30 seconds.


 
AAR90
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RE: Cabin Depressurization

Mon Nov 24, 2003 2:03 am

Airplay,

Sometimes its just not worth discussing a subject with someone who quotes specifications and regulations vs. someone who has lived the experience (it's not nice). Wonder why my hobbies would even be brought into your "discussion." Guess you should add me to your non-respected list.
*NO CARRIER* -- A Naval Aviator's worst nightmare!
 
airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: Cabin Depressurization

Mon Nov 24, 2003 11:16 am

AAR90,

I don't play the "respected user list" game. Its pretty subjective. I find those with tons of "respect" often don't make alot of sense but they provide popular answers that don't contain any contrary opinions (or facts in this case).

If we all just sit around blindly agreeing with each other, this forum would lose any value.

 
shaun3000
Posts: 439
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RE: Cabin Depressurization

Mon Nov 24, 2003 4:28 pm

Ya took Northam's class, eh, Pilotpip?  Big grin
 
Shenzhen
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Joined: Wed Jun 25, 2003 12:11 pm

RE: Cabin Depressurization

Mon Nov 24, 2003 6:18 pm

""The thing that always puzzled me about the accident was that, in my opinion, they overlooked one item - the Lear 35, while only certified to FL450 has the same pressurization system that is certified to FL510 in their other airplanes. The Lear's pressurization system has automatic cabin altitude limiters designed into it that make it impossible for the cabin altitude to go above 14,000' or so (Not 13,000' as you mentioned in your post.) in a structurally sound airplane. Remember the reports? The F-16 chase planes saw no evidence of airframe damage - only frosted up windows. 14,000' is hardly an altitude that will bring on terminal hypoxia.""

I think what should be pointed out here is that nobody knows what condition the airplane was in, so nobody knows if it could have been limited to 14K feet.

A simple example would be a ruptured duct outside the pressure vessel, causing a decompression. The airplane would look sound to a F16 pilot, whilst all the cabin air escaped through the big hole that was once a duct.

Plausible?
 
captjetblast
Posts: 289
Joined: Thu Aug 30, 2001 5:59 am

RE: Cabin Depressurization

Mon Nov 24, 2003 11:13 pm

Hey Liamksa:

"...maybe closely followed by your bowels)." ??

Oh my God, Can it happen? What an embarrasing situation!
 
Guest

RE: Cabin Depressurization

Mon Nov 24, 2003 11:28 pm

"...I think what should be pointed out here is that nobody knows what condition the airplane was in, so nobody knows if it could have been limited to 14K feet.

A simple example would be a ruptured duct outside the pressure vessel, causing a decompression. The airplane would look sound to a F16 pilot, whilst all the cabin air escaped through the big hole that was once a duct..."


Plausible? Of course. I could come up with several dozen "what if" scenarios that would cause it. The problem is that none of them are very likely. If I remember correctly, there has never been an example where a "51K" Lear pressurization system has suffered that type of failure which resulted in the cabin climbing above 14000'. And that's with a system that has millions of hours of inflight fleet history. Of course, anything's possible and we'll never know for sure.

Like I said in my previous post, the new information on the dry ice that was possibly in the Lear's baggage compartment, if it is found to be correct, would easily explain everything. It is very nasty stuff and is considered hazardous material. There have been several fatal aircraft accidents where dry ice has been involved. I bet our friend L-188 up in Alaska has a few stories about pilots, airplanes, fish, and dry ice.

Jetguy

 
EMBQA
Posts: 7859
Joined: Sat Oct 25, 2003 3:52 am

RE: Cabin Depressurization

Fri Nov 28, 2003 10:12 am

Well I can only go on what I have experianced. As a Mechanic, there are a couple of checks we need to do where we pressurize the aircraft on the ground, then do an 'Emergency Dump'. I've dumped at +1.5% Press. Diff, and if the conditions are correct, the temprature drops in the cabin so fast you can actually make it snow and your ears pop pretty good. Going on that, I really would not want to be at FL350 when the plane springs a leak....not fun.....
"It's not the size of the dog in the fight, but the size of the fight in the dog"
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Cabin Depressurization

Thu Dec 04, 2003 1:05 pm

To get back in the vicinity of the original thread here, maybe a related question . . .

Why a 30 - 74 second TUC at 30,000 feet but people have climbed Mt. Everest at 29,000' without oxygen. I can't accept that any amount of physical conditioning could so change your physiology that you could survive indefinitely at 29K but pass out and die at 30. Furthermore, I've heard a mountaineer say that the big problem of doing Everest without O2 is loss of body heat. Without supplemental oxygen you cannot take a step often enough to keep your temperature up.

Without the obvious commentary on the brains of people who would climb Mt. Everest in the first place, how can they climb it at all without oxygen?

One last thing, worth remembering. One common symptom of hypoxia is euphoria, the loss of the perception that anything might be wrong. Few aviators, and probably none at all who had not been through "the chamber" would ever notice their own oxygen starvation.
Happiness is not seeing another trite Ste. Maarten photo all week long.

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