Mexican low-cost carrier Volaris is expanding its U.S. routes just as bankrupt Mexicana de Aviacion prepares to return to service.

Volaris’s latest move into the U.S., which includes services from Mexico City to Denver and San Francisco and from Culiacan and Uruapan to Los Angeles, forms part of a broader network expansion that includes the addition of six Airbus narrowbodies to the 35 currently operated by the airline, Chief Commercial Officer Holger Blankenstein tells Aviation Week.

A further 44 aircraft are scheduled to be delivered between 2015 and 2020, he adds.

The two Mexico City additions will require waivers to the current bilateral air transport accord between Mexico and the U.S. because the two route authorities allotted to Mexican carriers are held by Aeromexico and Mexicana. Volaris is seeking temporary rights to Mexicana’s authority until Mexicana, which has been grounded since August 2010, resumes operating the routes.

While such waivers have previously been awarded to Volaris and rival Interjet with the understanding that the routes will be returned to Mexicana when it resumes those services, Mexicana’s planned return is being hindered, in part, by negotiations to regain control of routes from Cancun, Guadalajara and Monterrey held by Interjet.

Mexicana, so far, has given no indication that it intends to resume service to Denver or San Francisco, although U.S. West Coast destinations are targeted in the carrier’s planned revival, which is currently scheduled for August.