Loss of Pressurization

[ifleyelearz]

They had plenty of time to don the oxygen masks, IMO. I fly the same model Lear 35 that was in the Stewart accident, and in my yearly refresher I believe they said it had something to do with their oxygen system, or lack of. If my memory serves me correctly, I think they had it serviced @ the FBO in FL that morning.

 

[DenverDude2002]

I heard that the cabin depressurized in 5 seconds, how is that enough time for pilots to even react?

 

[CL60]

Tuc

DenverDude2002:

"I heard that the cabin depressurized in 5 seconds, how is that enough time for pilots to even react?"


Time of Useful Consciousness. Plenty of time in the FL20's.

 

[User546]

I heard that the cabin depressurized in 5 seconds, how is that enough time for pilots to even react?

Just because the cabin depressurizes rapidly, doesnt mean the crew loses conciousness immediately.

What factor plays in to this is the time of useful conciousness that the crew will have past that point for them to put on their oxygen masks and perform an emergency descent. At 35,000 feet you have upwards of 30 seconds of useful conciousness, and maybe a bit longer.

So at the lower altitude they were at when this happened would've given them even longer to react and take the appropriate actions.

There is obviously much more to this accident then any of us will ever know.

 

[KlingonLRDRVR]

Lost outflow valves in 2 lear 35's, different planes, different times, but both over the center of Lake Michigan at FL 330. Twilight zone, what are the chances of that! Actually pretty good in tired old dogs haulin checks. Both times, fat dumb and happy only to hear a thump in the back like someone kicked the plane, ears pop, and cabin climb meter is pegged. Pretty uneventful. Quick, don masks call center to tell them we are on our way down, pull out the spoilers and go down. I think at FL 330 you have around 30-40 seconds without O2. Odd ball maintence problems not that big of a deal if you haul checks for a living. You old frieghtdogs know what I mean. Now if you don't know what your doing on preflight with the O2 bottle in the nose and actually beleieve "on" means "on" in a lear you should not be flying one. If the valve on the Stewart plane looked on which really means off and lost cabin alt your doning the O2 mask would not do you much good. Sims are good practice so you know what to do in the real world.

KlingonLRDRVR

 

[FracCapt]

TUC times at the mid 20's are pretty good. In the mid 30's, not so good. See the page below for a chart.

http://www.halojumper.com/halobriefing.html

 

[Kream926]

never flown a pressurized jet and i dont have any experience besides what i know from whats on paper. but if i could chime in on this subject and say that going into one of them hyperbolic (?) chambers is a good idea. CAMI in OKC has one and for those of you in tulsa, TTC also has one. opens your eyes to what happens when sh!t happens. i found out because i smoke i get hypoxic waaaaaay before my non smoking ones do

 

[Lead Sled]

Payne Stewart

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 years ago, during one of our 6-month G100 FlightSafety recurrents, we were having 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 practically impossible for the cabin altitude to go above 14,000' or so in a structurally sound airplane. 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.

Nothing made a lot of 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.

If these reports turn out to be true, then this will change 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.

I'll second what Kream296 suggested. 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.

'Sled

 

[Daveman]

Nothing made a lot of 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.

If these reports turn out to be true, then this will change 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.

I'll second what Kream296 suggested. 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.

'Sled

I have heard the same story. You are 100% correct concerning dry ice. 'Sled, I don't blow smoke up the arse, but you are a legit, quality type guy.
I've learned from your previous posts' and will continue to do so, I'm sure.

I've lost the cabin at 18' and 41'. 18' wasn't too bad as I was in the descent,
41' wasn't rapid (Door seal). I take the rapid D in the sim seriously.

 

[ackattacker]

From the Carbon Dioxide MSDS:



Carbon dioxide is an asphyxiant. It initially stimulates respiration and then causes respiratory depression.
High concentrations result in narcosis. Symptoms in humans are as follows:
​

EFFECT: CONCENTRATION:
​

Breathing rate increases slightly. 1%

Breathing rate increases to 50% above normal level. Prolonged

exposure can cause headache, tiredness.

2%

Breathing increases to twice normal rate and becomes labored. Weak

narcotic effect. Impaired hearing, headache, increased blood pressure

and pulse rate.

3%

Breathing increases to approximately four times normal rate, symptoms

of intoxication become evident, and slight choking may be felt.

4 - 5%

Characteristic sharp odor noticeable. Very labored breathing,

headache, visual impairment, and ringing in the ears. Judgment may be

impaired, followed within minutes by loss of consciousness.

5 - 10%

Unconsciousness occurs more rapidly above 10% level. Prolonged

exposure to high concentrations may eventually result in death from

asphyxiation.

The cabin volume of a lear 35 is 268 cubic feet. The gas denisty of CO2 at standard temperature and pressure is 0.1144 lbs/ft3. The evaporation of 1.5lbs of dry ice would result in a 5% cabin volume concentration at sea level, even less at altitude. A definite danger!

​