While the company still has to combine the carriers' reservation systems, a single certificate will mean the Federal Aviation Administration recognizes the airlines as one, and that the majority of their flight, maintenance and dispatch procedures will be identical.

"Achieving SOC is a major milestone, but it does not mean that our integration is complete," the newsletter said.

The company recently said it will transition to a single loyalty program for frequent fliers on March 28.

The FAA could not immediately be reached for comment.

(Reporting By Jeffrey Dastin in New York. Editing by Andre Grenon)