In the latest betas, if you call
$routes_expanded = NavData::parseRoute($route_string);
It will expand out airways. There are still some bugs but it will be avail from 2.1. As for what it returns, it will return an array of objects, one object for each point which contains the coordinates and the type of point, and what airway that point belongs to. To get the distance, you can call SchedulesData::getDistanceBetweenPoints($lat1, $lng1, $lat2, $lng2), IIRC. You'd have to check the API for specifics