Frontier Airlines will bring back seven seasonal routes from Philadelphia International Airport in April.

Denver-based Frontier will add flights beginning April 21 to April 23 from PHL to Austin and San Antonio, Tex.; Nashville, Tenn.; Cincinnati, Ohio; Kansas City, Mo.; Milwaukee, Wis.; and St. Augustine, Fla. Frontier operated the routes last summer, but discontinued them in the late fall.

Frontier currently flies year-round from Philadelphia International to Charlotte and Raleigh, N.C.; Cancun, Mexico; Denver; Houston, Tex.; Orlando, Miami, and Tampa, Fla.; New Orleans; and Punta Cana, Dominican Republic.

Frontier will discontinue seasonal routes from PHL in April to West Palm Beach and Punta Gordo, Fla., said airline spokesman Jim Faulkner.

Frontier often adjusts routes in the spring and summer and again in the winter.

The airline switches aircraft to fly from cold to warm weather destinations in the winter. When weather is warm in the Northeast, Frontier flies to traditionally cold-winter destinations in the summer months, Faulkner said.

Frontier flies nonstop to destinations several times a week. The patterns are Tuesday, Thursday, and Sunday. Or Monday, Wednesday, Friday, and Saturday, Faulkner said. Some flights, such as Philadelphia to Denver, operate daily.

Frontier also flies from Trenton-Mercer Airport in Ewing Township, N.J. In April, the schedule from Trenton airport will be to Atlanta, Charlotte, Chicago O'Hare, Detroit, Raleigh, Ft. Lauderdale, Orlando, Tampa, and Punta Gorda, Fla.

Frontier, which uses the slogan "Low fares done right," said its average roundtrip fare was $108 for the 12 months ending September 2016.

While base fares are lower, Frontier charges extra for a carry-on bag in the overhead bin, advance seat assignments, and even a soft drink on the airplane. Passengers can pay for packages called "the works" and "the perks" that include a carry-on or checked bag, seat selection, priority boarding, a refundable ticket, and the ability to change a flight without a change fee.