There are a number of issues with Rotterdam X that can be solved through the use of your AI traffic program and the freely-available Airport Design Editor (ADE). The commercial product Airport Studio (AS) is recommended also as you can edit the airport while the simulator is running and see where you are putting things in relation to the airport ground textures. Fixing these issues has lent a much more realistic feel to the airport as the scenery looks amazing but does not function all that well when you actually use it. Let me just say right up front that modifying commercial scenery is okay so long as you do not distribute any of the files you edit, which is why I'm simply describing here the things I did for other people to consider implementing themselves. Perhaps Aerosoft would be willing to work some of these into a future update to the scenery.
Issue #1: Unclassified parking
<a href="http://www.blade-edge.com/images/avsim/rotterdamX/addendumParkingCodes.jpg"><img'>http://www.blade-edge.com/images/avsim/rotterdamX/addendumParkingCodes.jpg"><img src="http://www.blade-edge.com/images/avsim/rotterdamX/addendumParkingCodes.jpg" align="right" width="202" hspace="5px"></a>None of the parking spots in the airport are coded to accept certain aircraft, which will lead to GA craft parking in airliner gate spots. This isn't completely the fault of the scenery designers as assigning airline codes could cause issues for customers who are using AI traffic that doesn't use the codes they used, and also because there's no rule saying some commercial GA traffic can't be routed to a gate parking spot. But for the purpose of my scenery usage I want airlines parking at gates and all GA aircraft using ramps.
If you are only using FSX default traffic, then you can use ADE or AS' parking properties airline code drop down list to select the airline codes to assign to a parking location. If you use a 3rd-party traffic program like Ultimate Traffic 2 make sure you use the airline codes from that program as they can be different. If you are using extra traffic from packages like World of AI, they also may use codes different than what FSX has listed by default and your traffic program uses. To find out what code any aircraft is using, open up its aircraft.cfg file and look for the section(s) [fltsim.x] where x is a number. In these sections you will find the property atc_parking_codes. These codes are what you should put in the parking spot code list in ADE or AS.
Issue #2: Lack of GA parking
The default scenery does not include a lot of parking options for General Aviation aircraft and if you run your sim with a lot of AI traffic you can reach capacity easily as this is a high-volume GA airport. This means arriving aircraft will disappear from the runway when they can't locate an open parking space. The default airport has 13 ramp parking locations and now that I've made it so GA traffic can't use a gate spot this makes the parking situation even worse. To increase capacity I added 40 more parking locations. The tie down area west of the main tarmac can hold as many as 17 20' (radius) parking locations. I also added 2 20' and 2 33' parking to the end of Taxiway A. 4 33' and 4 46' parking spaces were placed over in the Jet Center parking area and 12 20' along with 12 33' parking spaces were squeezed into the rear tie down area at the end of Taxiway F.
I also made added a "JET" code to the parking spaces in the Jet Center, then went into my AI traffic aircraft.cfg files and added the code to the atc_parking_codes line in all the business jet aircraft so that only jets park in the Jet Center. Makes sense right?
<center><a href="http://www.blade-edge.com/images/avsim/rotterdamX/addendumXtraParking.jpg"><img'>http://www.blade-edge.com/images/avsim/rotterdamX/addendumXtraParking.jpg"><img src="http://www.blade-edge.com/images/avsim/rotterdamX/addendumXtraParking.jpg" width="250" hspace="2px"></a><a href="http://www.blade-edge.com/images/avsim/rotterdamX/addendumXtraParking2.jpg"><img'>http://www.blade-edge.com/images/avsim/rotterdamX/addendumXtraParking2.jpg"><img src="http://www.blade-edge.com/images/avsim/rotterdamX/addendumXtraParking2.jpg" width="250" hspace="2px"></a>
Parking layout for West Tiedown and Taxiway A (left)
and Jet Center and Taxiway F (right)</center>
Issue #3: Lack of names for GA parking
<a href="http://www.blade-edge.com/images/avsim/rotterdamX/addendumATCParking.jpg"><img'>http://www.blade-edge.com/images/avsim/rotterdamX/addendumATCParking.jpg"><img src="http://www.blade-edge.com/images/avsim/rotterdamX/addendumATCParking.jpg" align="right" width="250" hspace="5px"></a>None of the GA parking spots have names, which gives you limited options when you taxi off the runway and ask for a parking location - ATC will simply assign you an open spot somewhere in the airport that matches your aircraft's specifications. I went and named all 4 GA parking locations based on their position to the airport's center. So you end up with a West (Taxiway L), Southeast (Taxiway J) and South (Taxiway F) parking as well as Gate A (Taxiway A). Now when you pull past the hold short on arrival you can request to be sent to a specific parking area of the airport. If you still don't care you can do a generic parking request. Asking to be sent to a gate will always put you at Gate A if you are a GA aircraft small enough to park there. Another benefit is that when you go to start a flight at Rotterdam you can see from the list of parking options in the FSX Location window where in the airport the parking is located.
Issue #4: Runway extends onto threshold
AI aircraft only use runway properties to determine landing distance in addition to their own configuration settings - they do not follow PAPI or ILS glideslopes. Since Rotterdam X's default runway extends onto the threshold but does not have any threshold value of its own set in the runway properties, AI aircraft will see the beginning of the threshold as the beginning of the runway, which isn't correct as you are not supposed to land on runway thresholds. Larger aircraft will still overshoot the threshold on approach, but smaller aircraft like the Piper Cub will indeed land short of the actual runway markings. In some cases this will create a longer roll-out period for some of the larger aircraft to find their exit taxiway. To get aircraft landing as they should you need to shorten the runway length to 5,907 feet. The runway will shrink from both ends so you don't need to reposition it and this new length will expose the threshold and place the runway only under the runway markings.
Issue #5: AI aircraft taxi off the taxi lines
This is a relatively simple fix, although if you don't have Airport Studio you'll need to import an image of the ground textures into ADE so you can drag the taxi links over the taxi lines drawn onto the ground textures. Basically it's just a process of making the two lines lay on top of each other. There is a downside to making the aircraft follow the lines in that to do so you need to lay significantly more nodes to get the aircraft turning properly along the taxi line curves. AI aircraft taxi speed is determined by the distance between two nodes - longer the distance the faster the speed. Since you are adding more nodes and closer together you are effectively making aircraft take several seconds longer to taxi around the airport. The impact isn't huge, but it is noticeable if you happen to get stuck behind one of them. But if you can't bear to watch your AI aircraft taxi with apparent blatant disregard to taxi lines, this slightly reduced taxi speed is just something you'll have to deal with.
<center><a href="http://www.blade-edge.com/images/avsim/rotterdamX/addendumTaxi.jpg"><img'>http://www.blade-edge.com/images/avsim/rotterdamX/addendumTaxi.jpg"><img src="http://www.blade-edge.com/images/avsim/rotterdamX/addendumTaxi.jpg" width="250"></a>
Airport Studio with transparency enabled to see under the aprons and
taxiways so you can align to the taxi lines. Some links have been deleted
to expose the taxi line for this image</center>
Issue #6: AI aircraft don't hold short properly
<a href="http://www.blade-edge.com/images/avsim/rotterdamX/addendumHoldShortAS.jpg"><img'>http://www.blade-edge.com/images/avsim/rotterdamX/addendumHoldShortAS.jpg"><img src="http://www.blade-edge.com/images/avsim/rotterdamX/addendumHoldShortAS.jpg" align="right" width="250" hspace="5px"></a>AI aircraft look for a special hold short node when taxiing to tell them when to stop and ask for takeoff clearance on departure and stop and ask for parking on arrival. This node can be placed anywhere, although generally it's in close proximity to the runway so that ATC does in fact grant departing aircraft takeoff clearance - arriving aircraft don't care if the node isn't close to the runway. In the default Rotterdam X airport file the hold short nodes are too close to the runway, causing aircraft to taxi over the hold short lines drawn on the ground textures. To fix this we simply move these nodes back to just after the hold short markings (see image from Airport Studio on the right). This will have aircraft stopping just short of the yellow line and ensure that aircraft arriving taxi fully over the hold short marking before requesting parking. Some of the taxiway hold shorts are very far away from the runway, but those taxiways are only used for arriving aircraft and we don't care if the hold short is far from the runway.
<center><a href="http://www.blade-edge.com/images/avsim/rotterdamX/addendumHoldShort.jpg"><img'>http://www.blade-edge.com/images/avsim/rotterdamX/addendumHoldShort.jpg"><img src="http://www.blade-edge.com/images/avsim/rotterdamX/addendumHoldShort.jpg" width="250"></a>
ADE says our hold short nodes aren't close enough to the runway to work,
but the top one does. If you modified the runway to not use the threshold,
then that will indeed be too far away for the hold short on the bottom
to work, otherwise it will too</center>
Issue #7: AI aircraft don't follow proper ground movements
I've saved the most complex issue for last. Rotterdam is laid out so that it can use two parallel taxiways to bring aircraft in and send them out at the same time without any serious interruptions in traffic flow regardless of which runway end is in use. Recreating this in FSX is, I have found, not entirely possible thanks to limitations with the AI in the simulator. I may be wrong, but hours of research and testing have yet to show me otherwise. You can come very close though - I'd say my current implementation is about 95% effective and only every now and then do you see a plane behaving improperly. It has created issues with ATC giving the user proper taxi-in directions however. Where it may tell an AI craft to taxi in via the proper "arrival" taxiway, it could send a user aircraft down a "departure" taxiway depending on where they stop after the hold short line and call in for parking. While I never witnessed an AI aircraft vanish off the taxiway after arriving due to not receiving complete taxi-in directions, I have had ATC merely say to me "taxi to general aviation parking ." and leave out any taxiway directions.
So because it's not possible to guarantee proper AI movement or proper user communications with ATC, it's obvious why this wasn't included in the commercial product release. But if you don't mind a few glitches here and there in the fight for a more realistic FSX environment then it can be worth the effort to get this system up and running. In my review I showed Runway 06 ground movements. Here is a video showing proper ground movement for Runway 24.
<a href="http://www.blade-edge.com/images/avsim/rotterdamX/addendumR24.jpg"><img'>http://www.blade-edge.com/images/avsim/rotterdamX/addendumR24.jpg"><img src="http://www.blade-edge.com/images/avsim/rotterdamX/addendumR24.jpg" align="right" width="250" hspace="5px"></a>If you're interested in trying to get this ground movement system working, the most important thing you need to understand is how to control AI aircraft's departure from the runway. Taxi for departure is a trivial matter to set up and get functioning, arrival is the tricky part. Airplanes of different classes will land in different spots on the runway (smaller the aircraft, closer the landing to the runway threshold) and also slow to taxi speed over different distances (smaller the aircraft, shorter the roll out). Once an AI aircraft has slowed to taxi speed it will immediately look to exit the runway to a parking location via the shortest route possible. In some cases, this exit point may be behind them. Back-taxiing to a taxiway isn't an unheard of technique for smaller planes in the real world, but you have to account for this possibility and try to prevent this from happening in some instances. For example, when Runway 24 is active, you can't let small aircraft use Taxiway V2 to exit the runway, or else they will taxi back along Taxiway V and either cause an arriving and departing aircraft to end up head-to-head and stop taxiing and time out or the two aircraft will simply taxi through each other. The image on the right shows how you can "intercept" aircraft before a runway exit and lead them down the runway to a further exit (as long as that exit happens to be in the direction of parking - remember, shortest route is the main determining factor). Red is for R24 arrivals and green is for R06 arrivals.
<a href="http://www.blade-edge.com/images/avsim/rotterdamX/addendumDoubePipe.jpg"><img'>http://www.blade-edge.com/images/avsim/rotterdamX/addendumDoubePipe.jpg"><img src="http://www.blade-edge.com/images/avsim/rotterdamX/addendumDoubePipe.jpg" align="left" width="250" hspace="5px"></a>What if you have no choice but to deal with aircraft exiting off the same taxiway for both arrivals? In this case you will have to look into a double-plumbing system that will guide the arrivals down the proper taxiway depending on where they exit the runway onto the taxiway. In the image on the left, red is once again for R24 arrivals (you see it extend off the image to the right, where it connects to the runway in the previous image) and green is for R06 arrivals. Once on the taxiway these lines overlap - they are exposed side-by-side here to make it easier to see them. Blue lines represent the base taxiway network where no double-piping needs to exist as these taxi lines do not connect in any way that would lead an AI aircraft astray. For R06 arrivals, the first exit point is meant to capture the smaller aircraft like Piper Cubs before they try and back-taxi and the second is for small aircraft that need to back-taxi. The red exit you see is for aircraft that don't need to be pulled away from the Taxiway V2 exit as their roll outs take them far enough down the runway when arriving on R24.
I won't lie - getting this working was not easy. It was educational, I'll tell you that, but it took hours of testing and I must have come close to giving up at least 5 times. And again, it's not perfect. But it's close enough for me and maybe for anyone else out there willing to give it a go. For further reading on AI behavior I would recommend this wiki article from FSDeveloper. You might also consider tweaking aircraft dynamics to effect things like roll out distances to further control where airplanes exit the runway, however be warned that you would be tuning aircraft for one airport in particular - which may cause unforeseen effects when dealing with the plumbing system of other airports.