They think we're fools?

[Toad]

That's an outflow valve; roughly the size of a cabin window.

It almost never should fully close in flight, as the differential pressure is what keeps the air flowing thru the cabin and bag bins and out the valve. At higher altitudes it does modulate towards the closed position but unless you lose a bleed air source (less air available coming in) it shouldn't fully close.

In general, at all certificated altitudes, there is enough "supply" air coming in off the engines and through the air cycle machines (think "air conditioners") to overpressurize the aircraft. This valve modulates open and close to maintain a desired psi differential, usually somewhere around 8 psi in the upper range of normal cruise altitudes.

Wind rushes by this big hole at 500+ mph. Nothing gets sucked out except cabin air.

If you lost a cabin window, this valve would rather quickly modulate full closed. You might not be able to maintain cabin pressure but OTOH, it isn't necessarily the horrendous explosive decompression that Hollywood likes to portray with people blowing horizontally in the wind, hanging on to a seat belt strap.

[Mini D]

See Rule #4

[Mini D]

BTW toad... we had a fatal accident at the base where I was located because a co-pilot did not latch his gullwing hatch. Once they hit a certain speed, a vacuum was generated in the cabin sufficient enough to tear all of the pages out of the TO they had and fligh half of it out of the cockpit and the rest of the pages all over the inside of the cockpit. As the plan changed angle, it moved from a vacuum to a direct force and the wind slammed the cockpit down on the copilots hand.

Hell... drive down the road with the back window of your truck open and watch what happens to papers on the floor... then turn your fans on inside and watch what happens to them.

Never underestimate the power of the venturi.

[Mini D]

One other thing toad... you seem to be hung up on the "sucked through a small hole" syndrome here. I'm not advocating that at all. I am saying that a situation that can cause a rapid depressurization will lead to a more violent reaction due to the forces involved. More things could give way, **** will be pulled out the opening.

Hell, look at the link in this thread. A stewardess was sucked up and then plugged a crack in the fuselage until it finally tore open and she traveled through the opening. How do you figure that is possible? Not just that she was sucked up off of her feet, but that she then stopped at the opening? Small enough to stop her, enough force to lift her. The reason it's just one is because only one person was in the highest wind rush area generated by the pressure differential. Even the passengers in the seat would be protected (since 1st class all wind would be coming from behind).

It's not even remotely common occurance because in the past it has relied on aircraft structural failure to occur simply as an act of fatigue. But it's far from being impossible, and the risk of it being catastrophic are very real.

An airplain can have leaks and fly just fine. As long as they can meet the monitored pressures. It only matters if those leaks are something that can develop into something worse. Systems and structures are designed to prevent that from happening, but they aren't the absolute on the subject and throwing variables into the equation is the surest way to demonstrate that.

[Toad]

And I don't think you fully appreciate how cabin pressurization works.

A pistol bullet hole or even losing a window isn't a Hollywood catastrophe.

The amount of "input" air is variable through bleed valves. The amount of "output" air is regulated and variable too. The system is designed to compensate for fluctuations in both input and output.

Now, can you lose a piece or create a hole big enough to overcome the system's ability to cope? Yes, you can.

OTOH, the public's apparent belief that a stray round through the fuselage, just making a hole and hitting no vital lines/cables/etc. can bring down an airliner is based in Hollywood fiction.

Crack in the fuselage? I flew an L-1011 that had a crack about 10 inches long that was about a finger wide, ~ 1". Big crack. It was in the lower galley area, within the pressure hull. Guess what....nothing unusual was noted. There was ONE reason and ONE reason alone it was found. The Captain was a smoker and smoking had just been banned on board. It was his habit to go down into the lower galley near the oven exhaust fans and have a smoke on the long 4 hours flights. This time, he notice his smoke was drifting away from the fans, followed it and saw daylight through the hull. The aircraft maintained pressurization perfectly. It was determined that the aircraft had flown about a week like that when the catering driver that put the hole in the hull finally 'fessed up.

Now if you have a big enough hole...and we're talking several square feet or better.... and it happens suddenly, you'd get an explosive decompression that might move things around. However, it doesn't last long, as the pressure will equalize pretty quickly at 8 psi differential or less.

That is designed to equalize pressure. The pressure in the cabin would be much higher if it weren't functioning.

[/b]

Which is why there are both positive and negative pressure relief valves on an aircraft.

Sucking pages out of a tech order doesn't take all that much force. I lost a page out of a T-38 checklist binder while taxing with the canopy open in a light crosswind; of course the page was loose to begin with.

I am saying that a situation that can cause a rapid depressurization will lead to a more violent reaction due to the forces involved. More things could give way, **** will be pulled out the opening.

[/b]


I guess if you weren't set on

Originally posted by MiniD:

being stupid

[/b]

and weren't

Originally posted by MiniD: chosing to be about as ignorant as I've seen you

[/b]

you'd realize we're saying pretty much the same thing.

A stray bullet or two going through the cabin wall is no big deal. OTOH, a bomb or some other highly explosive device could cause a serious problem with the aircraft, primarily due to structural failure but which would also generate a short period of intense decompression.

[Maverick]

Mini D,

The scenario you are worrying about has already been tested many many times. It involves putting holes in non designed areas. The holes were of non uniform shape and size and rather randomly placed in pressurized aircraft at both high and low speed.

It started with the B29 in WW2. It continued with the B52 much later on. While you do get some "peeling" of the skin and a rapid loss of pressure you do not get a catastrophic failure of the skin and or airframe due to a small hole. Pressure would equalize very rapidly and be unable to maintain a pressure differential if the hole is large.

The airlines are not a pressurized sealed bottle. They are a pressurized semi sealed bottle with only a 5 to 8 PSI differential. They are not in a vacuum and if they were then there would be no "peel back" of the skin as there is no atmosphere to peel it back due to friction.

[Mini D]

Maybe I'm missing something here... did you two not read the article about the lady sucked up... clogging a crack and then sucked out of the plane?

In your perfect world... how is this accounted for?

I can put a hole in a panel or glass and it won't make a difference. If I hit a support structure, what happens? You think there have been studies, there have not been nearly enough. This I guarantee you.

And all of this boils down to the rapid loss of pressure and it's impact on the area of highest velocity. It is a far stretch to say "it wouldn't matter" or "it wouldn't be an issue". By a long shot. You cannot gather data to prove a negative. History has shown this to be the case. For someone who prides themselves on it, it's amazing how quickly they forget it.

And Toad... the relief valves are designed for reactive equalization, not constant equalization in the event of a catostrophic event. The whole goal is to maintain pressure within limits. This does not prevent events.

Let me put it another way: How does a pressure equalization system maintain pressure in case of a leak? What if the leak gets bigger? What if the leak get's bigger?

[Maverick]

MiniD,

If the leak is beyond the ability of the bleed air system to compensate for you get less than adequate pressurization. That's one of the reasons there is a pressurization indicator in the cockpit. The fuselage is not pressurized and held as a closed system. It's a constant flow pressurization with the bleed air being used for heating / cooling as well as pressurization.

I'll never forget the story told to me by a vet from WW2 when I was on a visit to the Pima Space and Air Muiseum (Tucson). He was a radio man in a B29 flying missions to Japan. He said he had complained several times that his station didn't have a window. Later on when the Japanese provided him with one he decided he didn't like it and covered it up with his empty glove. That allowed the leak to be stopped and maintained the pressurization of the aircraft. He wasn't belted in and didn't get sucked out of his seat much less the aircraft.

If you create enough damage particularly to a supprt structure you will lose the aircraft. That has already been shown to be the case especially with the first British jets. That is not the situation that was under discussion however. The question was regarding putting a bullet hole in the skin of a jet at altitude. Quite different.

[Mini D]

Look at what I said in regards to bullet holes.

Now look at how it's expanding to cover just about every opening. Windows... gaping holes... yeppers.

You can cite numerous examples where small leaks were contained. A bullet hole through a skin would be an easy one to contain. A bullet into an alluminum spar and then through the skin... well... that's another story. Structural weakening combined with depressurization.

The truth is, that there is an extra added risk with firearms in the aircraft. This simply cannot be denied. "It shouldn't cause depressurization" is a bit of a straw-man argument. It "can" cause depressurization is much more accurate and you will lose the argument as a result of it.

I'm all for firearms in the aircraft in the hands of highly trained personel like air marshalls. I'm even for the pilots having sidearms provided there are advanced training courses that accompany their presence. I'm just not about to pretend that there wouldn't  be an unintended consequence as a result of discharging the weapon in an aircraft.

[RAIDER14]

United Flight 811



Aloha Airlines flight 243



this should interest toad and mini d

[Toad]

The most interesting thing Raider is that those pictures were taken after landing.

I those pics pretty well sum it up right there. Catastrophic structural failure FIRST, coupled with explosive decompression AFTER the structural failure and the pictures are taken after landing albeit with what can only be regarded as minimal loss of life.

The Aloha suddenly lost 18 feet of the top half of it's fuselage. ONE Flight Attendant was "sucked out"...except the accident report states:

The No. 1 flight attendant had been standing at row 5 and was immediately swept out of the cabin through a hole in the left side of the fuselage. The No. 2 flight attendant had been standing by row 15 and was thrown to floor, sustaining small bruises.

 A "hole" in the left side of the fuselage? There was no "left side" of the fuselage left in First Class. The "hole" was 18 feet long. Note also that the No. 1 F/A was the ONLY fatality:

After the flight, there were seven serious injuries to the passengers, one serious injury to the No. 3 flight attendant, and one apparent fatality to the No. 1 flight attendant.

There you have the "Hollywood scenario"; 18 feet of fuselage missing. However, one fatality on an aircraft with 95 souls on board.

In the case of United 811, examination of the airplane revealed that the forward lower lobe cargo door had separated in flight and had caused extensive damage to the fuselage and cabin structure adjacent to the door. Five rows of business class seats, located at the top of the cargo door (the area with the most structural damage) were blown out of the aircraft, along with nine passengers. It is key to note that standing Flight Attendants were thrown to the floor but not sucked out. Passengers in the remaining seats adjacent to the hole were saved by their seatbelts.

This from a 15x3 hole in the fuselage.

I will take issue with the idea that a single bullet, even if it hit a structural fuselage member, would cause that degree of a problem.

[Toad]

Originally posted by Mini D
And Toad... the relief valves are designed for reactive equalization, not constant equalization in the event of a catostrophic event.  

Don't forget the blow-out panels.

[Mini D]

The floor will always be a good place to be. Sitting would be a decent place too... unless the seats give way. The air flow is strongest down the center and towards the opening. People farthest away will feel the effects less, closer will feel it much more since the air actually has to rush past them. This is all typical of any pressure variation situation. Once the air rush is over, you only have to deal with the low pressure problems such as fighting for air until the plane is slowed and drops in altitude.

You'd know that if you took a bit of time to actually think about it instead of just shaking your head.

[Toad]

The No. 2 flight attendant had been standing by row 15

Amazing she didn't get "sucked out" isn't it? Seeing as how she started out with just two feet on the floor. One would think the power of the venturi would have taken over. Same for the F/A's standing up in biz class on the United jumbo.

A bullet into an alluminum spar and then through the skin... well... that's another story. Structural weakening combined with depressurization.

Tell, which spar would you have to hit with one bullet to cause damage like that done to the Aloha or the UAL? Or would any spar do, you think?

[RAIDER14]

Cabin Pressure

Cabin Pressure 2