Meet TransDigm Group (NYSE: TDG), an aerospace company few have heard of – though it has posted average annual gains of 16% over the past five years and 17% over the past 10. The company went public in 2006 with a share price of $21, and it recently traded near $1,080 per share. But as of mid-September, its stock was down 19% this year, presenting an intriguing opportunity for longterm investors.