I was at DTW one time last year when all of a sudden I saw a bunch of firetrucks going down the taxiway, and go to the same terminal as pictured (Berry) and hose a Northwest 747-400. I talked to someone from Northwest and he said the pilot was retiring
Most likely the 744 is one of the most hosed airplanes in the Northwest fleet because don't you have to work your way up in seniority to be a 747 captain? So therefore most likely a lot of pilots retire in Northwest with the 747 being their last aircraft.
N661US is one of Northwest's oldest 744's but true it is not old enough to retire since Northwest still has plenty of 742's to retire first.