I'm a self-taught decorator and have been decorating for over 15 years.  I'm still baffled though by buttercream air bubbles??  Every time I watch tutorials on icing cakes, they always are icing cakes that are chilled.  I prefer to ice a cake that's chilled, but when I use my buttercream to ice a chilled cake, if the cake sits out for any length of time, I will get at least one huge bubble that forms.  I make my own icing using high-ratio shortening, is this the reason?  Would an all butter recipes not do this?  I'd totally appreciate any input!  As of now, I chill my cakes after baking and cooling them, but I bring them back to nearly room temp before covering with icing.  

I'm afraid I don't have an answer for you, the question has been asked quite a bit on here and nobody seems to know for sure. The one thing that always seems consistent though is that it's a powdered sugar/fat recipe, like American butter cream.

The meringue butter creams don't do it.

AWell, I guess it's a question for the magazine!!! Lololol!

I always ice a chilled, crumb coated cake.  Sometimes I get a bubble...it can start growing like a big 'ol tumor.  It's just the gasses being released from the temperature change.    One time I had a bubble appear later..at the person's house.   Now...after decorating every single cake..I take a straight pin and poke holes where no one will see it all around the base of my cakes.   I do this for evey cake...every time.   That one bubble freaked me out and looked horrible. 

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That's a great thought to poke the holes.  I've had a big huge bubble that grew and grew!  You're right!  They like to spread!  Lol!

You could try adding cream of tartar.  I don't have access to high ratio shortening where I live...but I do add half to one teaspoon of cream of tartar.  The one problem I don't have is air bubbles.  Give it a try...it does not change the taste or color of the icing in any way.  Sure hope it helps!

This happens on all types of icing and with fondant. It's air that warms up and expands and tries to get out from inside the cake. I do everything at room temperature and it happens to me too, so it isn't necessarily something that's just with cakes that are cold.

I wrote about this on my blog, but the main thing you have to do to avoid it is try to get all of the air out from between your layers when you ice the cake. If there are any pockets of air that are trapped they can try to get out and it will make a bubble. Poking a hole in it and pressing it back will fix it, but it's a PITA in the meantime. http://acaketorememberva.blogspot.com/2011/06/dreaded-cake-tumor.html

You've got to give the air a means of escape.  Either run a thin blade under the edge of the cake to break the seal of the bc to the board (yes it messes up the bottom edge, but if you have a border or a ribbon, no worries) or poke a good hole into the top center, which will eventually be covered by the tier above.  You can also poke a hole in the top tier if there's going to be a topper. to cover it, or you could repair that one later with bc.

If you forget all that and get a bubble, don't just poke a hole.  Use something small like a coffee stirrer and poke that into the bubble, and suck the air out.  Don't say eww.  You're not blowing into the cake and you're only touching the coffee stirrer.

It really does help is a preventive sort of way.  The thin blade at the base of the cake was one of the things I learned in culinary school.  I never got an air bubble when I remembered to do that.