I don't know if anyone can answer this question. Today, flights from Detroit Metro are taking off to the Northeast. On most days when the Northeast departures are used, flights from DTW going to Europe will continue on a NE heading until they are just past my house (I live 6 1/2 miles NE of DTW)....they will then make a slight turn and head straight North...I have watched many of these flights continue on the North heading with binoculars until they disappear from sight.
Today, however, I have noticed two Europe bound flights....a Northwest A330 and, no more than 5 minutes ago, Lufthansa's A340 turn to a East heading long before they have reached the area where I am located. But...there have also been 2 NWA 330's that have flown over and turned to the common North heading.
If anyone can explain why, I would certainly appreciate reading your replies.