re: Aviation Question

They actually fly in a pretty straight line on a route like that, they just have to adjust the heading due to their proximity to the magnetic pole. It looks curved because you're seeing the route on a map versus a globe. In general, the only reason a commercial airliner will turn in flight is to get into and out of the traffic pattern at it's departure or arrival airport or to change which airway route it's on for traffic control.

Planes also don't really fly level at cruising altitude. There's a constant up attitude to maintain level flight, it's just a matter of adjusting the attitude to maintain the proper elevation.