Realistic AI aircraft traffic at airports requires specifying multiple parameters in the WED scenery file.

The minimum requirements for successful AI traffic operation at an airport are:

  1. The airport is of type “airport”, i.e. not a “seaport” or “heliport.”
  2. The “Has ATC” property is checked in the metadata.
  3. Have at least one ATC frequency of type “Tower” defined.
    • Note this refers to the “Type” property, not the name given to the frequency entry, which has no relevance for AI operation.
  4. At least one (very preferably multiple) ramp starts of sufficient size is specified:
    • The size of the largest ramp start (of any type) must be larger or equal to the actual AI aircraft attempting to spawn/land.
    • X-Plane will not check if that ramp start is actually vacant or the right type – it rather gives ATC authority to make “emergency” decisions like parking a 747 on a Size A “Props” “Misc” ramp start, if none of the size F starts at that airport are available for some reason.
    • See the “Guide to Ramp Starts” for details on ramp start fields.
  5. At least one paved runway (surface = “Asphalt” or “Concrete” only) of sufficient width and length is active.
    • Active means either:
      • there is valid flow specification that meets the current weather condition and it includes a “Runway use” rule for that runway
      • or no flows are specified. In this case, X-plane will auto-generate suitable flows that activate all runways under any weather condition.
    • Sufficient width & length depends on the AI aircraft category as in the table below:

Aircraft category

Min. Rwy Width

Min. Rwy Length

Heavy

125 feet

10,000 feet

Fighters

125 feet

7,500 feet

Jets

100 feet

7,500 feet

Turboprops

75 feet

2,500 feet

Props

50 feet

2,500 feet

Anything else

25 feet

1,000 feet

These are all conditions to make AI spawn or attempt to land at the airport.

It also implies the actual ramp start types and ATC taxi network details do not prevent AI operation, but only help to make it look more “plausible” once AI are present at the airport. A working ATC Taxi network, either auto-generated by X-plane or specified in the scenery is required to have those AI successfully leave the runway and taxi to/from the ramp starts.

Troubleshooting Tips

To debug problems with AI operations it is recommended to start with hiding all user specified flows and ATC taxi networks in the WED scenery pack. X-Plane will then auto-generate these items, which will result in functional flows & networks, although they will also appear less polished.

By default, the X-Plane log.txt also includes information about AI spawning, flow selection and AI Taxi instructions. The art control atc/debug/log_spawn=1 prints log info on AI aircraft arrival & departure logic. Use the developer console to see this in-sim or view it in the log.txt

5 comments on “Guidelines for AI aircraft airport use

  1. Support Grass runways!

    Is the decision to need paved runways a technical limitation (eg AI really behaves badly on grass – big fix required) or more of a sweeping generalisation from back-in-the-day when X-Planes airports were ‘plausible’ rather than the curated beauties they are today?

    1. It’s due to a limit in the sophistication with which ATC analyzes the airport layout. Chris started digging into the ATC code again recently, and this is one I’ve had on my radar to re-evaluate at some point.

      At a minimum, I expect we will be able to allow airports with grass runways that are longer than the longest pavement if the flows are built by hand – basically if the author tells us things are okay then they’re okay. If the airport layout is autogen, that’s a lot harder, as grass tends to just be a big blobby area.

  2. This explains a lot. I couldn’t figure out why jets stopped spawning or landing at my airport with a 7,000 ft. runway. I also couldn’t figure out why I couldn’t begin an AI flight in my own aircraft from the 7,000 ft strip.

    It should be noted that the Cirrus Jet can takeoff in 3192 ft. and land in 1628 ft.

    Similarly, the Challenger 300 requires 4,810 ft. for takeoff and 2,600 ft. for landing.

    The numbers for the Phenom 100 are 3,199 ft. and 2,430 ft. for takeoff and landing, respectively.

    737’s and 320’s can easily operate from 5,000 to 6,000 ft. runways – not at maximum takeoff weight or high and hot, granted – but at medium weights.

    I have flown B757 IRL in and out of 5,500 ft. runways in the Caribbean with not issues. Also at reduced weight, but with no issues.

    Any chance the restrictions could be lifted for jets?

  3. What are the actual criteria for spawning AI aircraft? I tried AI jet aircraft at several airports with runways considerably less than 7,500 ft. – Midway, John Wayne, Aberdeen, Gibraltar and London City. With the exception London City, all airports with these short runways spawned jets, although the guideline says the runway has to be 7,500 x 100 ft.

    The runway at London City is 4,948 x 98 ft. When I increased the width to 100 ft., it would not spawn jets, however, when I increased the width in increments, it would spawn jets on anything 100.3 ft. or greater.

    I stopped testing at that point since it is obvious that the guideline is incorrect.

    Would it not be simpler to base the spawning criteria on the maximum ramp start and taxi route size? It seems incongruous that the ramp starts can spawn the specified size for static aircraft but not for AI aircraft.

    Cheers!

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