It took me close on 10 years of climbing on helicopters to finally slip off one... and I was just thinking of it when I saw my foot go one way it wasn't supposed to. Luckily it was only off the skid but I ended up with a slightly damaged ego and cracked wrist...
Best thing to do, paint all steps with a non slip paint of some sorts... and be careful because like hueyracer says, you'll end up creating more problems than you want...