I was looking at Frontier Airlines #857 for December 5, 2010 and the flight path has the customary “green” line from Denver to Phx. However, next to it are blue “dashes”. The dashes, at one point in the flight, veer way off the green course. What does this mean?
Just a nervous flyer here. I’ll be on this flight next week. 
Thank you for any insight you can give.
The green line is actual tracking. The blue dashed line is the flight’s planned route. Planes often don’t follow their planned route for numerous reasons such as being cleared direct to a particular navigation waypoint by ATC, weather avoidance, traffic, etc.
Looking at the particular flight in question, it’s unclear to me why the route would be so weird. Perhaps an error when filing the flight plan? I dunno.
At any rate, no need for concern over your plane’s routing/flight path. Your pilots and the controllers handling the flight know where you’re going and how best to get you there safely.