I found flight tracker today. I noticed flight schedule from Kansas City to Las Vegas Vanguard #721. The flight tracker was shown Allegiant Air Flight #721 at the same time schedule. Did Vanguard ask Allegiant Air to borrow MD80 flight for reason? Maybe one of the MD 80 have problem or under maintenance. Did anyone who know about this information? It also Allegiant Air flight #902 flew Denver to Kansas City this morning, too.