MIDNJAC said:
not to get off topic, but could someone explain how this works? It would seem to me that there would be a delay between when the window was blown out, and when the pressure system could actually restore local cabin pressure. Clearly this is not the case (as I'm pretty sure that HAL and A4's know what they are talking about), but I'm just curious how the system compensates for this??
Air is drawn into the plane via the air conditioning system. This air pressurizes the plane. How much it pressurizes the plane is dependent upon how much of the air you let back out of the plane. The outflow valves are how the air is let back out of the plane. The DC-10, for example, has 2 outflow valves. One is the size of a front door and the other the size of a single car garage door. When the plane is unpressurized, the outflow valves are completely open. As you climb, you pressurize by slowly modulating these doors closed. At some point, normally the plane's max altitude, both doors will be almost fully closed. They will never be closed completely.
Yes there will be a delay while the electric motor drives the outflow valve closed but I believe that you could probably restore pressure to the cabin except near the max altitude. A window size opening is not that big relative to the outflow valve. Closing the outflow valve to reduce airflow out of the plane from there could probably compensate.
A bullet sized hole would not even be noticed by the pressurization system.
Neither would cause a catastrophic failure of the fuselage.
nkawtg said:
When a pax window blows out there's no way for ANY system to compensate/restore cabin press again. The only thing left to do is an emer descent and hope that everybody on board will keep their hearing abilities.
P ambient will be P cabin within seconds, so time is a factor if you fly at high altitudes. At great heights oxygen is insufficient so everybody needs oxygen from their ox generator to prevent hypoxia.
I disagree. At the planes max altitude this would probably be true, but I think you could stay in the mid flight levels. It would be extremely noisy, windy and cold, but you could regain/control pressurization so the mask would not be needed after the intial event.
I'm not saying its a smart thing to do, but over water you might need to stay higher for fuel reasons.
firefriendly said:
There wouldn't be a catastrophic "explosion" where half the plane is shredded. However, if there was sudden decompression from a hole, depending on size, where the hole was created, and the structure surrounding it...it could potentially rip some things open. There was an accident in the 70s or 80s where a flight attendant was up and about and there was sudden decompression, i think somewhere over hawaii. She plugged the hole for a second then got ripped out. ......
heres one example of what decompression can do
http://avstop.com/news/american3.html
and the one i was talking about
http://en.wikipedia.org/wiki/Aloha_Flight_243
A hole cause by metal fatigue or some other failure of the fuselage would definitely have the potential to expand or rip things open. A bullet hole probably would not or at the most cause very little additional damage.
The American flight you linked too was on the ground and all indications in the cockpit were that the plane had depressurized like it was supposed to after landing. I recently attended some sim training at the AA training academy at DFW. Although not an AA class, my ground school and sim instructors were either AA working a second job or furloughed AA. They discussed this accident during our pressurization systems training, There was a malfunction in both the pressurization system and the indicating system. The plane had a 0.125 psi pressure differential from ambient (which is what most airliners have at landing). The FA was not sucked out. As the FA was opening the door (which swung outward), there was just enough of a pressure differential for the door to "pop" open. The FA did not let go of the door handle as it "pop" open and lost his (her?) balance. With the FA holding on to the handle the doors weight and momentum were enough to pull the FA out of the plane. The FA was killed because he landed on his head. Although not depressurizing completely is not common, FAs have always been trained to not hold onto the door handles of outward for just this reason.
