Airline stocks have endured a year of turbulence, reflected by wild swings in share price, industry expectations and earnings. Recent insider trades of airline companies could indicate where the industry will head next. The Trades: Benzinga Edge compiles information on insider trade filings. Southwest Airlines Co (NYSE:LUV) experienced a flurry of insider activity in recent days. Director Rakesh Gangwal invested over $100,000,000 in Southwest shares in late September and early October. Executive Chairman Gary C Kelly bought $1,000,000 of Southwest shares in late September. Delta Air Lines, Inc…