On March 15-16, 1982, Frontier Airlines inaugurated service to two additional cities in Mexico. The round-trip inaugural between Albuquerque and Manzanillo was on March 15, while the round-trip inaugural between Albuquerque and Puerto Vallarta was on March 16. Boeing 737-200 aircraft were used for both inaugurals. 

The Puerto Vallarta Post Office applied a special cancellation in red as a backstamp.

This cover was one of only 179 pieces of mail carried on the inaugural Frontier Airlines flight from Puerto Vallarta, Mexico to Albuquerque, New Mexico (where it was backstamped) and is listed in The American Air Mail Catalogue as FL-D55N.

Frontier Airlines’ shareholders and the Department of Transportation approved the airlines’ merger with People Express on Tuesday, November 21, 1985, officially ending Frontier Airlines’ 39-year era as one of the west’s major independent air carriers. People Express, based in Newark, N.J., bought the Denver-based Frontier Airlines on October 9, outbidding Texas Air Corporation and a coalition of Frontier unions. With the Department of Transportation’s actions, Frontier Airlines officially became a wholly owned subsidiary of People Express, Inc.

On August 24, 1986 Frontier Airlines ceased operations and released all of its employees as the result of financial difficulties. On August 28, 1986, the airline filed for bankruptcy under Chapter 11 of the Federal Bankruptcy Code.

On October 17, 1986, the bankruptcy court approved the purchase by Continental Airlines’ parent corporation, Texas Air, of the assets of Frontier Airlines. The Frontier acquisition was one of several conditions established by Texas Air as requirements for its acquisition of People Express, Inc., Frontier’s parent company. The equipment and routes of Frontier were sold to Continental Airlines which reinstated many of the old Frontier routes using the purchased Frontier equipment and by rehiring many of the old Frontier employees.

Continental Airlines continued to operate the Frontier jet fleet with the aircraft being repainted in Continental's livery. On March 3, 2012 Continental Airlines merged into United Airlines.