Watch skies for traffic patterns, illusions

Q: There is a busy stream of flights overhead traveling north and south, usually from the Northeast and Europe to Florida. I use Flightradar 24 to identify the flights and destinations. The planes usually fly in a very narrow corridor right behind one another. Sometimes this is 50-100 miles offshore, sometimes it is 50-100 miles inland, sometimes it is right over me. What determines this?

— Mike Kennedy, Wilmington, N.C.

Answer: There are airways along the area you reference. Also, there are military warning areas. If the military is using certain airspace, civilian airplanes have to avoid it. Depending on the day and weather conditions, controllers will assign specific airways for the Northeast-to-Florida traffic. This would account for what you are seeing.

Q: On some days you can see numerous contrails, and on other days there seems to be no flights at all. Why is this?

— Gregory Goodwin, Indianapolis A: The flights are there but the atmospheric conditions to produce contrails are not.

Q: I live 5 miles north of Detroit Metro Airport. It appears that when the 747 flies over, it is flying much slower than the MD-80s do. Is that an illusion?

— Robert Williamson, Westland, Mich.

A: It is an illusion due to the size difference. The 747 flies at about the same speed as other airliners.