Inspired by Coach getting his fat arse exhausted in the opening cinematic of L4D2, how many flights of stairs can you climb until you start to tire yourself out?
 
I start wheezing at 12 to 15. Yeah, out of shape..

Been a few years since I actually did stair running for fitness, last I remember was back in the rowing season of early 07. Probably about the same, can't remember too well though. :/

I have to climb loads of stairs in my house so I never get tired on them anymore.

 What girdz said, up and down them all day if I'm in uni, the building design is terrible, and on certain sections you can't get across the floors, so you have to go down to go back up at the other end. At a guess I'd say around 20 on a good day.
 
Although "maybe the helpicopter, maybe it's made out of chocolate", if it really is made of chocolate, I probably could do it alot quicker.
Only if it was high quality chocolate though, like Bournville or flake, but then a flake helicopter seems liable to failure.
This poses another question, what chocolate is most suitable for helicopters. 
God dammit your question is deeper than you thought.
If you turn this upside down it's like stairs.
Unintentional till now!