Loss of Pressurization

[Checks]

Good information!

 

[Peardc10]

Pressurization problems

I've had a few of them,

The first one was on a DC10, we were taking an aircraft from the A/C boneyards of AZ to GSO for refurbishment and was at FL370, when we noticed that the cabin was climbing 1500fpm, we did the checklist and found out that we could not control the cabin and delcared an emergency and went to 10,000 ft so we would'nt drop the masks. We continued to GSO at 10,000 ft and eventually landed with one generator working. The aircraft was in terrible shape sitting in the desert for over a year. Found out that a piece of insulation blew out the relief valve and got stuck in the valve, so we had a hole the size of a grapefruit venting air out the cabin........wonderful.

Another incident occurred when I flew corporate in the midwest flying a Lear 35. We had just purchased a used 35 and was doing some flight tests on the A/C when we were at FL270 when the cabin went thunk, the pressure controller failed and the cabin went blewy. We donned the masks and declared an emergency and returned to the airport. Pretty wild when the cabin vaporizes and everything on the floor is jettisoned in the cabin. I dont think it was the same problem that happened to Payne Stewarts 35.

My 2 cents.

SEEEEEEEEEEEEEYA!

 

[CL60]

Lead Sled,

Is the O2 sys on/off valve on this model Lear located on the outside of the airplane? Id est., not accessible while in flight?

One of my more notable emergency scenarios, (not a Lear), occurred out of FL430 with a decom. (Yes, one of us had a mask secured while in cruise... doesn't everyone do that?). Cabin rate pegged going up and subsequent very high cabin alt. Emerg descent/divert with pax. You can tell right away that you have O2 flowing at 100% with positive press up there .

If the O2 sys in the Lear was off or failed, at lower altitudes I'm sure it is possible to breathe ambient air through the mask and not immediately realize it.

 

[FastCargo]

Altitude Chamber...

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

I'll jump on this bandwagon. Military guys all get this type of training at the beginning of their careers, and get refreshers every 5 years (at least in the USAF). Not only do you get a great idea on what happens during rapid decompression, but you get good information on your own personal signs of hypoxia. This includes exercises in how your motor skills decrease, how night vision is much worse, etc. This has saved more than a few people throughout the years. If there is a chamber nearby and you can afford it, I highly recommend the training.

Plus, as a bonus, it's much cheaper to get drunk that night!

FastCargo

 

[TristarCostar]

The Lear 35 has one of the worse oxygen systems ever designed. On the 35A I used to fly a few years back you had to check the bottle during the external walk around and check to see if it was on. The bottle being mounted on the inside right of the nose. Also, if you looked at the way the bottle was mounted with the top of the bottle to the right, you would actually see the word "off" facing you. Actually, that was the "on" position and vice versa. We always had problems with the system. Like I said, one of the worst systems ever designed but still a kick ass jet to fly! Hope this helps. The other bad flaw of the system is that you had no access to the bottle from the interior of the airplane. Once in the air, you were on your way or going back!

 

[ifleyelearz]

The Lear 35 has one of the worse oxygen systems ever designed. On the 35A I used to fly a few years back you had to check the bottle during the external walk around and check to see if it was on. The bottle being mounted on the inside right of the nose. Also, if you looked at the way the bottle was mounted with the top of the bottle to the right, you would actually see the word "off" facing you. Actually, that was the "on" position and vice versa. We always had problems with the system. Like I said, one of the worst systems ever designed but still a kick ass jet to fly! Hope this helps. The other bad flaw of the system is that you had no access to the bottle from the interior of the airplane. Once in the air, you were on your way or going back!

Try flying the military version of the 35...the C-21. Not only is the O2 bottle not accessible in flight, it is located up by the tail (not in the nosecone). You have to get a ladder in order to check the bottle. Your only assurance that the O2 system is working fine is to put the mask on for a while to make sure you're still getting O2, during the preflight check. Then its checked again via the masks during the cruise check. The O2 gauge in the cockpit only shows bottle pressurization, which does you no good if you have a fully charged bottle, but the knob is rotated to the 'off' position.

 

[Lead Sled]

The Lear 35 has one of the worse oxygen systems ever designed.

Learjets: The best technology money could buy... In 1958.

'Sled

 

[some_dude]

I believe the dry ice theory has been disproved at least according to the NTSB.

This aircraft did not have the 510 system with automatic emergency pressurization. It had the older system, which used the windshield heat for emergency pressurization.

Ultimately, we will never know what the cause was. All my comments are speculation. So, for what little it's worth:

An instructor at FSI Tucson gave me the most plausible explanation I've heard. First, for some reason they did not receive supplemental oxygen. The O2 valve was found in the on position, per the NTSB report. Either they didn't put the masks on, or they were low or out of oxygen.

Then, if they had some sort of pressurization problem and tried to troubleshoot it per the checklist, and had the "IN NORMAL/OUT DEFOG" knob in the wrong position, they would have shut the bleed air off and the bleed air system would have been configured as it was found in the wreckage. No air coming into the cabin.

Honestly, I have a hard time remembering where that "IN NORMAL/OUT DEFOG" knob is supposed to go, and I've been flying Learjets for years! The poor PIC in this accident only had 60 hours in Learjets. It was a bad design, and fixed in the 510 system. The NTSB addresses this scenario, but can't prove or disprove it.

Oh, and for you altitude chamber advocates, that is a good thing, but in this case the PIC was a former military pilot and emergency procedures instructor. He had plenty of altitude chamber experience.

Anyone who is interested in this accident should look at the NTSB's website. Lots of good info.

http://www.ntsb.gov/events/aberdeen/default.htm

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

 

[some_dude]

Oh, and on the subject of dry ice, here is a very interesting NTSB report.

http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001211X09850&key=1

 

[User546]

Then, if they had some sort of pressurization problem and tried to troubleshoot it per the checklist, and had the "IN NORMAL/OUT DEFOG" knob in the wrong position, they would have shut the bleed air off and the bleed air system would have been configured as it was found in the wreckage. No air coming into the cabin.

I have a hard time imagining that there was enough of the aircraft left to even be able to know where the switches were set. I figured a nose dive from the kind of altitude, and the ensuing monsterous hole it drilled into the ground, the aircraft wouldn't be much more then a crushed tin can. (??)