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Caution, hold position - very, very annoying!!

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Now I know that the whole AI thing was new in FS2002 so we have to expect one or two problems (which hopefully will be tackled in the next version....) but this one is now really bugging me because it begins to make a bit of a mockery of all the more dense AI flight plans that result in a fair bit of traffic movement around the taxiways.What is happening is that traffic is being given the message 'caution hold position - other traffic' and that's the last they ever hear. Long after the 'other traffic' has moved away they are still left hanging until, in one case a 777 taxying to the gate which had to hold for a taxying Baron, eventually disappeared.I've noticed it particularly in my Kai Tak scenery I guess because there's only one long main taxiway which gives a potential for conflict between traffic taxying for take off and aircraft leaving the runway after landing. But I've also noticed it away from there elsewhere on the field as was the case with the 777 and the Baron.But also more seriously, once the message has been given out, all new movements are given the same message until the wole field grinds to a halt (aircraft are given taxy clearance and then told to hold position immediately even when there is no traffic conflicting with them and it doesn't take long for one plane blocking a rwy exit to have another queued behind it on the rwy, thus preventing all landings).I can't see any obvious solution. I thought originally it was down to having 2 and 4 hr repeats that were too tight so an aircraft landing was immediately in conflict with 'itself' needing to take off but I redid my times and have crawled over them with a fine tooth comb and can't find any problems.I guess I'll just have to grind my teeth and reduce my aircraft movements by 50% or so, so the potential for conflict is reduced. But I can't say I like it!!:-grr Roger

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Most of these kinds of problems can be solved by a good AFCAD design. Most AFCAD designs I've seen don't do a lot to make sure traffic moves around freely. You can't just lay down every single taxiway at an airport and put in the gates and assume traffic will move around without any problems. The designers also need to study the traffic flows and figure out the best way to move traffic. Sometimes this means deleting certain taxiways, removing hold short nodes, or using other techniques.For example, if you look in the two pictures below, the first one shows how most AFCAD designs look. This will cause aircraft to freeze up because eventually you are going to get two aircraft meeting from opposite directions.The second picture is a design that gets rid of this problem. All the gates are attached to master nodes so that aircraft will either wait for another to pass before proceeding or they will taxi around each other. There are many other techniques like this that can help with traffic flow.Most of these problems don't become apparent until after about 15 minutes when arriving aircraft start trying to enter gate areas at the same time departing aircraft are leaving.Matt

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Here's a real world example of the above picture showing master node technique from a radius AFCAD Aaron and I have been working on for KORD.Matt

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Thanks Matt - very interesting. I'll have to think on this one a bit more. Roger

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I had similar thoughts Matt, so I decided to put em to the test. OK, here's what I've done, that seems to have solved the problem.This is for rwy 31 - Kai Tak is 'special' because no AI will land on rwy 13 because of the mountain directly on the approach (I'm gonna look at an offset ILS sometime). I don't want to close 13 for landings because when you are flying IFR manually it makes for a really interesting approach and landing.What I've done is break the main taxiway at (1) in the pic making it into two segments (A1 and A2). This means that the only route to the rwy 31 hldg point is along the top taxiway, then turn rt and left at (6) onto A2.I've also removed exits at (2), (3) and (4) so any a/craft landing on 31 can't leave the rwy before position (5).So now I have a circular flow with only 1 potential point of conflict at pos (7) and although it WILL happen at sometime, I guess, I've had no problems so far. If it does, I'll try removing the diagonal link to (7) but this will only shift the problem as there has to be a cross-over somewhere.A/craft landing on rwy 13 is academic as I've said. If they could, obviously I'd be in trouble if they can't exit at (5), not because of a ground traffic conflict but just because of the time it would take for them to taxi right to the other end of the rwy to get off.Obviously we have to think carefully in future about our taxi flows because my experience shows that it's easy to bring an airfield grinding to a total halt if you're not careful.Hope this is of interest to other AFCAD users.Roger

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Looks like you've found a good solution. In most cases it just takes some time thinking about traffic flow to figure out a good design.Let me know ifyou have problems with aircraft getting stuck in the gate areas I have a trick for that as well.Matt

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>"You can't just lay down every single taxiway at an airport and put in the gates and assume traffic will move around without any problems."Exactly! Traffic flow and queuing space is critical!I also have had problems with large-radius a/c not getting centered on the departing runway. I typically add a node on a 45^ angle so that they will start their turn earlier.

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