Happily not yet "normal" but quite legal. Legislation was passed four or five years ago legalising armed flight crew on American airlines as a "security" measure.
As you can imagine, this was pretty controversial among aviation professionals.
FYI, there has even been talk of America asking permission for its pilots to be armed when flying to international destinations. See this article from a couple of months ago:
http://www.usatoday.com/travel/news/...ots-guns_x.htm
I can't imagine that being popular in many countries.
Bobbsy