Shares of Chicago-based airline heavyweight United Airlines (UAL) have not had a good time on the bourses of late, declining 23.8% in the past 90 days. The disappointing price performance resulted in UAL underperforming its industry’s 5.6% decline in three months. It also underperformed the S&P 500, of which the airline is a key member. However, UAL’s price performance compares favorably with that of fellow U.S. airline operators American Airlines (AAL) and Delta Air Lines (DAL) in the same timeframe.Three- ...