Unbelievable letter to editor. USA Today

[AWACoff]

A Walter Kline sent a letter to the editor of USA today. In it, he stated that an airline pilot who had written a previous letter did not know her aircraft has an outflow valve. He based this conclusion on a statement by her explaining how a bullet hole in the pressure vessel could cause a rapid decompression. Since there is already an outflow valve, a bullet hole would be "inconsequential", states Mr. Kline. He then stated the biggest safety factor is an airline pilot who doesn't know the systems of the aircraft being flown. UNbelievable. Reminds me of the time a private pilot came to the cockpit after a flight. He proceeded with a list of "squawks" he had discovered during flight...yaw damp inop (nope, that's turbulence), the exhaust stack of the right engine was loose (nope, that's how the engineers keep it from breaking off), and best of all, he noticed a vibration (no SH!T...it's a Brasilia for pete's sake!). I hope Mr. Kline can assist other flight crews in the future should they need his expertise. How embarrassing (sp?) to be so ignorant that you don't know you're ignorant (hey, that's ME!). I got a good laugh out of it (as well as sending a letter of my own to the editor).

 

[bobbysamd]

Hey, AWACoff

Check your private messages.

 

[A Squared]

AWACoff

Unless there is more to the letter exchange that you haven't repeated, I would tend to agree with Mr. Kline, a half inch hole in a fuselage is not going to vent air faster than the pressurization system can keep up with it. I hope that you didn't embarrass yourself with your letter.


Regards

 

[surplus1]

A Freshman: He who knows not and, knows not that he knows not.

A Sophomore: He who knows not and knows that he knows not.

A Junior: He who knows and knows not that he knows.

A Senior: He who knows and knows that he knows.

PS: In the world of airplane driving, the Senior is the most dangerous.

 

[cherokee]

Hmmmmm

Ummmm, not sure if you realize this A Squared but during pressurized flight the outflow valve is not fully open. If it was the plane would never pressurize. Just as the plane will not pressurize when on the ground because the safety valve is open. The valves are the same size. See what happens the next time you're pressurized and flip the "DUMP" switch. You've just opened the safety valve. You will have rapid decompression just as you would if the outflow valve was fully open, or yes, a 1/2 inch bullet hole. Go for it AWACOff.

 

[A Squared]

Okay,

I'm thinking in terms of larger airplanes. Perhaps with airplanes of the citation/kingair/brasillia size, a half inch hole would be significant. I know that on the DC-6, there is a manually controlled outflow valve to regulate pressure when the normal regulator fails. I haven't measured the opening personally, but it appears to be at least 3 " in diameter. It is controlled by a circular "butterfly valve" even if the butterfly is just barely cracked open, it's gonna be letting a lot more air out than a half inch diameter hole. I'm pretty sure that a DC-6 pressurization system could keep up with a bullet hole.

How large is the outflow valve on a Citation? King Air 200? Brasillia?

regards

 

[tdvalve]

IHMO, an extra half-inch hole in the pressurized fuselage of an airliner would have no effect on cabin pressurization. There's air leaks galore on most large aircraft, and excess pack flow can easily handle an extra half inch hole. In fact, some airlines operate single-pack for fuel economy.

 

[avbug]

a .5 hole in the pressure vessel will likely do little or nothing. Anybody who has ever had their aircraft shot up in flight can attest to the fact that it takes a lot more than a few rounds, (excepting those placed in the unfortunate wrong spot) to bring an aircraft down).

The hollywood image of a gun being fired inside a pressure vessel and then an explosive decompression is rubbish. It's insanely stupid. Every bit as much as aircraft rolling over and spinning in when the engine quits.

Do this. Shut off your bleed air at altitude. See how long it takes to bleed down. You may be surprised how fast the cabin will depressurize. This is why there is a constant flow of air, and why we don't simply blow up the airplane like a balloon and seal it off. The cabin will leak down, and regular leak down tests are part of most all maintenance programs (weather you're aware of it, or not).

Do you really believe that a bullet hole in the side of the pressure vessel, considered only for the size of the hole, will contribute much to vessel leakage? If so, you're in error.

However, a round may strike wiring bundles, coax, or any number of other vulnerable points. Additionally, a panel or structural member is reliant on it's own strength, and the strength of the surrounding member. A weakness in one area may cause other areas to fail. It's not so much the pressure leakage through the hole, but the potential stress riser caused by the rupture in the metal. This may lead to a tear, or other form of failure (crack, etc).

I'm not aware of any cases in which a shot or two caused a structural failure in an aircraft, let alone a rapid decompression (except on the silver screen). It's a ridiculous arguement.

Mr. Kline is quite correct.

 

[publisher]

lightening

It is sort of one of those things like lightening. Which is worse to the pilot, the actual lightening or the trubulence around it.

The biggest danger of a bullet is that it goes through the pilot

 

[AWACoff]

I guess I'm the only one who took issue with Mr. Kline's cheap shot at the other pilot (and potentially scaring the flying public about airline pilots not knowing the systems on their aircraft).

Maybe some of you with military experience are more in the "know" but do all bullets leave half inch holes? I have little experience with projectiles passing through "hard" materials so I am unsure about what the effect(s) are. I didn't infer in my letter that the bullet hole would bring the aircraft down. However, being unable to control pressurization at altitude is a serious matter. The perfect "half inch" hole sounds like a best case scenario. I do not recall how large the outflow valves on a Brasilia (or Doinker for that matter) are. What I do know is this. Upon takeoff from SPW one night, we had a stuck outflow valve. Stuck in the open position. The aircraft would not pressurize. If you are up at max cruise altitude (8000ft cabin) and have an uncontrolled "opening" in the aircraft, the cabin alt. will climb. I would imagine different types of ammunition could create fairly large (1-2 inches) holes. Unfortunately all of my experience has been in small aircraft (e120, do328). A half inch hole is a much larger percentage of the pressure vessel on a brakillya than a 777. Enough of my rambling.

PS. On the note of making a fool of myself...it bothers me not. I do it routinely every Thursday night.

 

[RJones]

I have to pipe in on this one.

The problem with a bullet hole as I see it, is that the bullet will be tearing the skin creating cracks, thus the skin has lost it's structural integerty and with that the hole will get somewhat bigger, how much is anyones guess, and if it's an explosive decompression is also a guess. If a person took a drill to the aircraft while in-flight the results would be much different, quite simply after pulling the drill out the pressurized air would escape with little or no effect and the pilots wouldn't notice it up front.

Military fighter aircraft have skins that are much thicker and thus can withstand several rounds, the amount of rounds it would take to down that fighter would have to be counted after it's impact with the ground.

I wouldn't suggest that anyone try firing a bullet through the pressure vessle, nor drilling it just to see what happens. I have to imagine that someone has done some research into this.

I'm not totally convinced that the pressure vessle would explode or wouldn't explode, however, my feeling is the hole from a bullet would create a bigger one, just how much as anybody's guess.

RJ

 

[profile]

Seem to recall it calculated in the past that the MD-11 could probably lose 2 cabin windows and still hold the cabin at normal cruise altitudes. 3 windows and it would start losing pressure, but not that fast.

 

[Buschpilot]

I'm going to take RJones perspective on this. A projectile moving through any physical body is going to leave more damage than you or I can see.

And besides, Mr. Kline said that a bullet hole in would be "Inconsequential". What caused that bullet hole to appear in the side of a Transport Aircraft?

That might be consequential.

 

[RJones]

Generator scoop is plugged?

Buschpilot,

Is the generator scoop plug still in? Re: your picture of the Garrett.

Thanks for taking my position.

RJ

 

[I.P. Freley]

There are holes and then there are HOLES

I do know that the Saab 340 can lose ONE cabin window and still keep the cabin pressurized, so a single bullet hole would have to do a hell of a lot of damage to create a hole large enough to cause an explosive decompression...

 

[Tri-holer]

Gotta say we flew the cargo version of the Triassic jet and there was no way we could operate with just one pack at altitude cause of all the holes, what with the hole they cut for the door and the "slightly" lessened level of maintenance in resealing holes in the pressure vessel during checks and such.

I am sure the cumulative effect was much more than a half inch hole.

I know that on one flight, (oddly enough, a day flight), I looked at the bottom of the entry door at altitude and saw a 1/4 to 1/2 inch gap. Good packs.

 

[skydiverdriver]

I once spoke to a DHL pilot who said he wasn't worried about bullet holes, since he took off with a plane full of holes anyway. Perhaps a bullet might cause other damage than just a small hole, as the damage might do more. Anyway, my contention is that if someone was trying to take over my aircraft, I hope I hit the fuel tank, if they give me a gun. One aircraft crashing over flyover country is way preferrable to hitting a building full of people.

 

[bart]

It is very simple guys, if you carry a weapon on your aircraft, spend some time at the range every month so the bullet ends up going into the perpetrator and not through the fuselage.

Also, make sure you use the lightest hollow point rounds you can find and no target is considered hit without two shots in it.

 

[profile]

The military has had some experience with this and so it is not just speculation to say that aircraft can maintain pressurization when full of holes from small arms fire.

 

[AWACoff]

Right about the time I think I know what I'm doing, I get a hard reality check. I don't know how you guys know how many windows you can be missing and maintain pressurization. The first thing that comes to mind is the FA dinging you with an urgent message about somebody opening their window....yikes. Thanks for setting me straight. I have heard the phrase "It is better to be thought a fool than to open one's mouth and remove all doubt". Oh well. I'm sure most of you knew that about me by now. See Yoooooooooo!

PS. Seriously...WHERE did you guys get the info for how many windows your aircraft can be missing and still maintain cabin???