Delta Air Lines appears to have fundamental strengths that are not currently reflected in its stock price. In the second half of 2016, all legacy carriers including Delta, American Airlines, United Continental and Southwest Airlines saw a rapid increase in their stock valuations as market sentiment improved for the entire sector. Even Warren Buffett, who has been a long time skeptic of the sector, ended up investing billions in major airlines. However, these legacy carriers have been on a roller coaster ride year-to-date and have underperformed the broader S&P 500 index.