Thanks for the replies. You are both right, they are under a single certificate and have been since Sep. '07. It was two years to the day from the initial announcement of the "merger" so I expect the timeframe of the Delta/Northwest single certificate would be about the same.
abutterfinger25 I don't think the livery has anything to do with the operatig certificate because US Airways started re-painting the America West planes only a few months after the merger was approved. Likewise Delta has begun to re-paint some of the former Northwest aircraft as well, most notably the 747 fleet.
What was confusing me about the US Airways operating certificate is that for the most part their labor is still divided between former America West and legacy US Air. The pillot unions are still in negotiations and the flight attendant contracts don't come up for renewal until next year I believe. The huge issue is seniority. My neighbor who was a very senior flight attendant with America West will, when the flight attendant workforce is combined, be much lower in the "pecking order" when it comes to choosing work schedules and vacation time.