The US Federal Aviation Administration (FAA) is proposing to fine Volaris (Y4, México City International) USD735,000 for allegedly operating an aircraft that was not in compliance with US Federal Aviation Regulations (FAR).

The regulator alleges that on March 12, 2013, Volaris returned a US-registered A319-100 to commercial service following the completion of heavy maintenance.

However, the FAA claims that during that inspection, mechanics allegedly failed to ensure that safety tasks including the removal and replacement of an emergency slide, verification that ailerons were properly rigged, and verification that the aircraft’s weight and balance calculations, were undertaken in line with the Mexican LCC's maintenance manual.

Though Volaris did tend to some of the outstanding matters following an FAA inspection on March 19, it did not, however, attend to the weight and balance calculation.

"On April 4, a subsequent FAA inspection found that Volaris allegedly still had failed to complete the inspection of the weight and balance calculations," the FAA said. "Additionally, the inspection found the company had allegedly failed to perform the required inspections for two additional tasks related to the heavy maintenance: a right wing slat seal edge replacement and a nose landing gear spring nut replacement."

In light of the above alleged violations, the FAA claims Volaris operated the aircraft in a state of non-compliance for a total of 121 passenger flights before bringing it up to spec.

Volaris has 30 days from receipt of the FAA’s enforcement letter to respond to the agency.