Our developer discuss about your question today, because the routing logic is so complex, and it don't have a function just like the DrawCore in our layers.
And we roll back to see what's the requirement here, we found the routing cannot solved your requirement.
It looks you want to find some alternative airlines between two cities, but it looks the airline is different with the route on land. It have some special rule and if it's a alternative airline, generally the stops won't be more than two cities.
So what you need is arrange the requirement again and then build your custom strategy about how to choice stops, after that you should want to update your data to set level for your airports.
For example, when we don't choose direct flights, the reason should because the price, or the weather reason. If that's because price, your strategy need to query the other data source which contains dynamic price for each airline. If that's because reason, you need to choose as few as possible stops and avoid the bad weather lines.
If you think about this, you can found our routing totally cannot handle the scenario.
If you want to get some suggestion about how to implement that based on our map APIs, I think you can create a polygon or circle between your start point and end point, then loop all the cities in this area, and you can build your custom logic based on your strategy after that. Our map API can help you do spatial query and spatial computation, but the other logic besides that should be complete by your custom code.
If I misunderstand your requirement or you want to get any more suggestion, please feel free to let us know.
Wish that's helpful.