Fares as low as $147* available at FlyFrontier.com until May 22 DENVER, 2013-04-22 — /travelprnews.com/ — Frontier Airlines today returns nonstop service between its Denver, Colo. (DEN), hub and both Harrisburg, PA (MDT) and Knoxville, TN (TYS). Both routes will operate seasonally with three weekly nonstop flights. To celebrate this service, fares as low as $147*… Read the full press release