Sending airplanes skyward has become tedious, even for major airlines that seemingly have done so smoothly for years. Flight frequencies have been stunted by too few workers amid an ongoing labor shortage and rising operating costs. In turn, airlines have started relying on America’s roads for help. With a growing demand from South Jersey, American Airlines is investing more resources into the shuttle service it began two years ago as a way to ferry passengers between Atlantic City’s and Philadelphia’s international airports. What was three daily trips from Atlantic City to Philadelphia schedu…