Northwest DC-9's, as usual...
That's something we talk about a lot in airliners.net. You can't miss posts about NW
DC-9's when you come to the forum. Northwest is expecting to retire its last DC-9 in 2010, replacement could be either the B-717 (however I doubt it because that one doesn't seem to have a future), the Airbus A318/319 or the EMB-190.
Northwest has three different DC-9 variants, the 10, the 30 and the 50.
The 10's are gone, if not gone yet there are very few left, they have been replaced with Avro RJ
The 30's which make up the majority of the DC-9 fleet at Northwest could in my opinion be replaced in the long run with a mixture of A318's/319's and EMB-190's.
The 50's coulc be replaced with additional A319's.