Hey Belgarath whilst you're here busting airplane myths:
Can a 747 do a loop ?
When smoking on planes was legal the air inside had to be refreshed more often, which resulted in better air quality than we have now that they've banned it.
Smoking also allowed the engineers to locate microscopic flaws in the skin of the plane. The smoke would be sucked out of the holes and leave tarry trails.
A 747 could do a loop, but I don't know if the airplane could take the g-loading coming out of the loop. It wouldn't be a nice pretty circle either, it'd be very lopsided. Any airplane can do a loop if you start the maneuver with enough energy (think speed). The thing which would cause the problem would be pulling out of the dive before you hit the ground and before you overspeed the aircraft and start losing bits.
Airplanes use compressed air which is bled off the engine. This air is cooled and then passed into the cabin. Now, if you were to just keep blowing the air in, you'd cause the plane to explode, so the way that the pressure is controlled is with an outflow valve. If you close the outflow valve more, you increase cabin pressure. Opening the valve decreases cabin pressure.
So knowing that, you can ask the question. If that air isn't replaced, and considering that there aren't a bunch of plants breathing carbon dioxide on the plane, doesn't it make sense that you need to replace the air fairly regularly? And that's exactly what happens. Now different individual aircraft types will filter air to different degrees. Smoke would gum up all of these air systems to a considerable degree.
Smoke COULD find holes, but that's not how they did it. Heck, this accident happened before smoking was banned:http://en.wikipedia.org/wiki/Aloha_Airlines_Flight_243
(Well, I think it happened right about the same time as smoking was banned. Within a month)
I can remember being on airplanes back then. They were AWFUL because smoke permeated the cabin. Airlines made smokers sit in the back of the plane (generally because the outflow valve is located aft and thus the air typically moves from the front to the back)
If there was a change in the way air was recirculated, it would be driven by fuel savings, not less smoking.