The airline's sales have excellent momentum, and its long-term shift toward the premium end of the market is paying off.Delta Air Lines (DAL -1.48%) stock flew higher by 13.2% in March, according to data provided by S&P Global Market Intelligence. The move comes after management updated first-quarter trading, and Wall Street analysts upgraded the stock with aggressive price targets.Delta Air Lines expects a strong first quarterThe first-quarter update came up at the J.P. Morgan Industrial Conference in mid- ...