Traffic

TCAS, synthetic traffic, Bluebell, LiveTraffic

NextATC deals with two completely different kinds of traffic. Do not confuse them.

TCAS traffic — aircraft published over X-Plane's TCAS datarefs by X-Plane AI, LiveTraffic, XSquawkBox, or another publisher. The plugin observes this traffic. It uses it for safety checks (runway crossing and takeoff clearances, VFR landing, AutoFly, pushback and Follow Me) and shows it on the Nav Display, but it cannot give these aircraft instructions.
Synthetic traffic — aircraft generated by NextATC itself, shown on the ground and in the air around your current airports. This is the built-in traffic system. It is experimental.

You can use both at the same time, only one, or neither. Only one plugin can own X-Plane TCAS publishing at a time, so Publish to X-Plane TCAS/map may be blocked if LiveTraffic, X-Plane AI, or another publisher already holds the TCAS slots.

TCAS traffic#

If a TCAS publisher is running (X-Plane AI traffic, LiveTraffic, XSquawkBox, etc.), nearby aircraft appear on the Nav Display automatically with callsign, altitude, speed, and source context where available.

You do not need to configure anything for TCAS traffic. If no publisher is running, traffic markers are empty by design.

Synthetic traffic (NextATC built-in)#

This is the synthetic traffic generator. It spawns aircraft on the ground and in the air around the airports you fly out of and into. The traffic uses airport taxi/runway data where available and follows a scheduled airport-board flow for departures and arrivals.

Turning it on#

The first time you enable synthetic traffic, an experimental disclaimer dialog appears. You must accept it before traffic spawns. This is intentional — the feature is still maturing and may behave oddly in some edge cases.

After acceptance, traffic spawns gradually as you approach an airport.

Configuration#

Traffic controls are split between two places:

Plugins -> NextATC -> Options -> Traffic — sections Traffic, Synthetic Traffic, Traffic 3D Labels (spawn limits, TCAS publishing, 3D rendering, label appearance).
Plugins -> NextATC -> Traffic (its own sub-menu, parallel to Options) — quick toggles and model setup: Aircraft Model Libraries..., Traffic engine, Publish to X-Plane TCAS/map, and Enable Traffic at Startup.

The most used Options controls:

Traffic amount — selects one total budget for ground and airborne traffic. Airport profile and local time adjust the effective count within that budget:

| Mode | Total flights | Density | | --- | ---: | ---: | | Low | 1–14 | 25% | | Medium | 2–28 | 50% | | High | 3–45 | 75% | | Ultra High | 4–60 | 100% | | Nuts | 8–90 | 100% |
Publish to X-Plane TCAS/map — publish synthetic aircraft over the X-Plane TCAS datarefs.
Draw 3D aircraft — draw the synthetic aircraft in the world. See Options Reference for the full list including 3D-label controls.

Settings are stored in:

X-Plane/Resources/plugins/NextATC/traffic_settings.ini

Bluebell CSL aircraft models#

By default, synthetic traffic uses simple visual models. To make it look like a proper airport, install the Bluebell CSL package via Plugins -> NextATC -> Traffic -> Aircraft Model Libraries.... The dialog reports whether Bluebell is installed and offers an automatic download. The expected install folder is:

X-Plane/Resources/plugins/NextATC/CSL/

The automatic downloader installs the core packages only: BB_Airbus, BB_Boeing, BB_GA, BB_Jets, and BB_Props. Repaint and virtual-airline add-on packs are skipped. When the downloader completes, the plugin reloads CSL models and regenerates synthetic aircraft; manual installs may still require reopening the dialog or restarting X-Plane.

Local IVAO X-CSL aircraft models#

The IVAO X-CSL aircraft models come from the X-CSL Library. Install and update the library with its official X-CSL-Updater, available from x-csl.ru/downloads; NextATC uses your local copy and never downloads or redistributes X-CSL files.

NextATC has initial support for an IVAO X-CSL library installed separately by the user at:

X-Plane/Resources/plugins/IVAO_CSL/

This is the default installation root. In either Aircraft Model Libraries or Options you can paste another macOS, Linux or Windows X-CSL path, including one shared with LiveTraffic, or restore the default with the dedicated button. The selected path can be the conventional installation root containing CSL, the model-content folder itself such as LiveTraffic/Resources/X-CSL, or a parent containing exactly one valid X-CSL library as an immediate child. NextATC identifies the content from its package metadata and accepts the library when it contains usable aircraft; aircraft with missing or damaged files are skipped, shown as a warning in Options and listed in IVAO_XCSL_problems.txt in the NextATC plugin folder.

Open Plugins -> NextATC -> Traffic -> Aircraft Model Libraries... to scan, validate and select it instead of Bluebell. NextATC only reads this local installation: it does not download, install or redistribute IVAO X-CSL files. Install and maintain the library separately. The two libraries are never mixed; model and fallback selection stays inside the selected library.

LiveTraffic / external TCAS publishers#

NextATC reads X-Plane's standard TCAS datarefs, not an interface specific to LiveTraffic. Aircraft published by LiveTraffic, X-Plane AI traffic, XSquawkBox or any other compatible TCAS publisher enter the same reader, so there is no separate "enable LiveTraffic" switch and no publisher is treated differently. From each aircraft NextATC receives only what TCAS carries: position, altitude, heading, ground speed, vertical speed, a Mode S identifier and the callsign. An aircraft with an empty callsign, or with a callsign that is not made of letters and digits (one inner hyphen, as in B-78HW, is allowed), is ignored: it is neither shown nor used in safety checks. Placeholders such as ?0001 are therefore skipped.

To avoid stepping on a third-party publisher you can turn Publish to X-Plane TCAS/map off so synthetic traffic stays inside NextATC's own renderer and Airport board instead of being exported to X-Plane TCAS.

When traffic starts with X-Plane through Enable Traffic at Startup while Publish to X-Plane TCAS/map is on and another plugin owns TCAS, NextATC shows an on-screen message naming the likely owner when it can identify it.

What NextATC does with external TCAS aircraft#

Nav Display: they appear on the map with their callsign and a generic aircraft symbol, because TCAS carries no aircraft type. Hovering a marker shows altitude, ground speed, heading and vertical speed.
Runway crossings: before clearing you to cross a runway, and again just before the clearance is transmitted and at your readback, ATC checks for an aircraft on the runway, on short final, or on final close enough to reach the runway before you have crossed. If it finds one you hear "hold short runway 24, traffic on the runway" or "hold short runway 24, traffic landing" followed by the callsign and, for landing traffic, its distance on final. The crossing clearance follows automatically once the runway is clear.
Takeoff: the same check runs before the takeoff clearance. An aircraft waiting ahead of you on the way to the runway gives "number 2 for departure behind" followed by its callsign. While you wait at the holding point ATC checks again and clears you once the runway is free. If traffic appears after the clearance was issued, ATC cancels it with "cancel takeoff clearance, hold position".
VFR landing: while the runway is occupied, ATC tells you to continue the approach and clears you to land once it is free.
AutoFly: when AutoFly flies your aircraft, it stops behind an aircraft close ahead on its taxi route, and waits at a runway crossing, at the holding point or before takeoff while an aircraft is on the runway or crossing in front of it.
Pushback: the aircraft being pushed and the pushback tug watch aircraft on the ground. The push waits for a moving aircraft, or ends early before a stationary one; the tug slows down, stops or takes another way around an aircraft blocking its route.
Follow Me: your Follow Me car stops for aircraft moving on the ground and plans its route away from them. Aircraft standing still do not affect its route or speed.

The tug and the Follow Me car only see aircraft and NextATC's own vehicles. Airport vehicles of X-Plane or of other plugins are not published anywhere NextATC can read, so the tug and the car do not avoid them.

What NextATC cannot do with external TCAS aircraft#

The principal limitation is the information contained in generic TCAS data. It provides observations such as position, altitude, heading, velocity, vertical rate and an identifier when available. It does not provide a complete flight plan, assigned runway, SID or STAR, taxi route, clearance state, radio state or a reliable declaration of what the aircraft will do next. NextATC can observe that an aircraft is aligned with a runway, but it cannot know whether it will land, go around, overfly the airport or disappear because its data source changed. On the ground, NextATC can observe that an aircraft has stopped, but it cannot know whether it is holding short, parked, waiting for another aircraft or about to move again.

This still allows useful conservative decisions for your aircraft. NextATC can hold you because an external aircraft appears to be on final, but it cannot guarantee that the aircraft will continue its approach. It can protect you from observed crossing traffic, but it cannot command that traffic to stop. It can stop you behind an observed aircraft, but it cannot instruct that aircraft to keep its speed, extend its approach or go around. NextATC does not talk to external aircraft on the radio.

In the current version, also:

Generic TCAS traffic is not connected to the built-in aircraft coordination. The built-in aircraft driver coordinates NextATC's own flights and your aircraft, but it does not import external TCAS targets: built-in aircraft do not stop, yield (give way) or keep spacing for LiveTraffic, X-Plane AI or other external aircraft, so the two kinds of traffic can conflict when you use them together.
Deriving the complete active runway configuration from observed traffic, or coordinating built-in aircraft around external traffic, is not implemented.
The IFR landing clearance does not check external traffic.
ATC gives no airborne traffic information about TCAS aircraft.
NextATC has no interface through which another traffic plugin could receive NextATC clearances or report its intentions.

The reason is not a missing setting: controlling or coordinating external traffic would require a two-way operational protocol that every traffic plugin would have to implement and agree on with NextATC (see the next sections). Aircraft of NextATC's built-in Traffic engine do not have this limit: NextATC knows their routes, runways, taxi paths, holding points, flight phases and clearances, and can make them hold short, cross, line up and wait, take off, go around, give way and follow a replanned taxi route. That is what makes coordinated runway use, exact hold-short compliance, controlled go-arounds, taxi replanning and congestion resolution possible.

Publishing NextATC traffic to X-Plane TCAS#

There is also support in the opposite direction. When Publish to X-Plane TCAS/map is on and NextATC can acquire X-Plane's traffic slots, it publishes its built-in Traffic engine aircraft through X-Plane's standard TCAS datarefs. This makes them available to X-Plane's own traffic display and to other consumers of the standard TCAS feed. X-Plane allows only one plugin to own those publishing slots at a time. If LiveTraffic or another plugin already owns them, NextATC cannot add its aircraft to that same TCAS feed; if you want NextATC to publish instead, disable TCAS publishing in the other plugin and restart X-Plane. Built-in aircraft nevertheless remain visible through NextATC's own 3D renderer, Nav Display map and Airport board, while NextATC continues reading the other publisher's TCAS targets.

Why NextATC cannot control or coordinate external traffic plugins#

Observing external traffic is very different from controlling it. For an external traffic engine (LiveTraffic or any other traffic plugin) to participate at the same level as NextATC's own traffic, publishing a position and a few additional intent fields would not be sufficient. It would need to expose a stable and coherent operational model for every aircraft: identity and lifecycle, complete route and active fix, assigned SID and STAR, runway and parking assignments, taxi route and current route segment, hold-short and crossing state, clearance history, pending instructions, radio acknowledgements, and the aircraft's ability to comply with each possible command. NextATC would then need to interpret and maintain that model, while the external engine would need to accept operational commands and guarantee that its movement system applies them.

Both sides would have to agree on the precise meaning and timing of states such as holding short, runway vacated, line up and wait, cleared to cross, cleared for takeoff and go around. They would also need to handle delayed updates, disappearing targets, rejected commands, route changes, plugin reloads and incompatible versions without allowing the spoken clearance and the aircraft's actual movement to contradict each other. At that point the integration would no longer be generic read-only TCAS awareness: it would be a full two-way operational protocol that both products would have to implement, version, test and support continuously, and every traffic product would have to agree on it with NextATC.

With a TCAS-only target, full operational control is therefore not possible, because the interface contains neither an authoritative intent model nor a command and acknowledgement channel. Such an integration is theoretically possible if a future traffic source exposes sufficiently rich and reliable capabilities, but it is substantially more complex than reading standard TCAS data, and no such protocol exists today.

Advantages of the built-in Traffic engine over external traffic#

This is where the built-in NextATC Traffic engine has a fundamental advantage. Although it is still experimental, NextATC owns the operational and movement state of its synthetic flights. It knows their routes, assigned runways, taxi paths, holding points, flight phases, clearances and intended next actions. More importantly, NextATC can make those aircraft obey its decisions: a built-in flight can be told to hold short, cross, line up and wait, take off, go around, give way at a junction or follow a replanned taxi route, and after landing it vacates the runway and reports it. Its clearance, radio response, route and physical movement are parts of the same system.

The difference extends far beyond knowing an aircraft's current position. For each built-in flight NextATC retains its departure and destination airports, assigned departure and arrival runways, parking positions, IFR or VFR status, cruise level, ordered route fixes, current active fix, and named SID and STAR where suitable procedure data is available. Even where a procedure is simplified or incomplete, NextATC still knows exactly what it assigned and which part of that route the aircraft is following. On the ground, NextATC owns the actual taxi rails rather than merely observing a moving symbol: the intended taxi route, the progress along it, the holding point, the runway entry point, planned runway crossings, the destination parking position, and whether the aircraft is taxiing out, holding short, crossing, lining up, rolling for takeoff, landing and vacating, or taxiing in. It also has operational state that generic TCAS does not contain: whether IFR, taxi and takeoff clearances were requested and issued, whether landing, parking and runway-crossing clearances were granted, whether a crossing has been vacated, whether a line up and wait instruction is active, and whether the corresponding radio exchange has completed. This allows the radio state, the movement state and the visible aircraft behaviour to agree with one another.

What built-in traffic can do that external traffic cannot#

The built-in Traffic engine does not need to reconstruct or negotiate this information across a plugin boundary: the ATC logic and the movement engine share the same flight plan, route progress, taxi geometry, operational state and clearance results directly. That is why SID- and STAR-aware route progression, consistent clearance and readback exchanges, exact hold-short compliance, coordinated runway ownership (one takeoff clearance per runway at a time), controlled go-arounds, taxi route replanning and active congestion resolution can be delivered much more reliably for traffic owned by NextATC.

Traffic jams illustrate the difference particularly well. Position data can reveal that several aircraft have become blocked, but resolving the situation requires much more: the system must know each aircraft's intended route, which route segments conflict, which aircraft has priority, which one can give way, and whether a safe alternative path exists, and it must then be able to stop, release or reroute the right aircraft. The built-in Traffic engine already coordinates its own runway queues and ground routes, applies priorities (taxi-in traffic before taxi-out unless an aircraft is already committed), holds aircraft for conflicts and can replan some opposing taxi situations. Your own aircraft is part of this coordination; external TCAS aircraft are not. These systems are experimental and still being improved, but they are possible only because NextATC owns both the ATC decision and the movement.

External awareness and built-in traffic are complementary#

NextATC is compatible with traffic plugins that publish standard X-Plane TCAS data, such as LiveTraffic, X-Plane AI or XSquawkBox, for awareness, not for control. Generic external traffic awareness makes your own operation safer and more coherent, and it stays generic: when reliable information is available through X-Plane's standard interfaces, it does not matter which compatible publisher supplied it. Observed traffic could contribute more to runway-use decisions, departure protection, arrival spacing and ground conflict warnings in future versions, and the developer is open to using reliable external information where it genuinely improves the simulation. However, the deepest coordination will remain much easier, and in some cases only possible, with traffic whose complete state and movement are owned by NextATC. The built-in Traffic engine provides the end-to-end control needed for coordinated runway operations, truthful radio exchanges, reliable hold-short behaviour, sequencing and active congestion resolution.

"I see no traffic at all"#

Walk down:

The Traffic engine is enabled if you expect synthetic traffic.
A TCAS publisher is running, or synthetic traffic is enabled and the disclaimer was accepted.
You are near a populated airport (synthetic spawn ramps up close to airports, not over the ocean).
On the Nav Display, use the Flight Plan tab for map markers and the Airport tab for the synthetic Departures/Arrivals board.

"Synthetic traffic flies into me"#

Synthetic traffic respects basic separation but it is not a real ATC. If you see a conflict, report the airport, flight phase and aircraft involved. Use the built-in reporter or attach the affected readable X-Plane/Log.txt to a web bug report; see Bug reports and feature requests.

"Bluebell models do not show"#

The Bluebell folder is in the right path (Resources/plugins/NextATC/ CSL/).
Plugins -> NextATC -> Traffic -> Aircraft Model Libraries... reports "Bluebell OK".
If you installed manually, reopen the Bluebell dialog or restart X-Plane.
Some aircraft types may not have a matching CSL model — those use a fallback model.

"A synthetic aircraft is stopped and does not move"#

Hover over its marker on the Nav Display map. While a synthetic aircraft is held and stopped on the ground, its tooltip shows stopped: followed by the reason: departure sequencing, traffic ahead, traffic queue, runway occupied, opposing taxi traffic, crossing traffic, traffic too close, traffic conflict, traffic safety. When the blocking aircraft is known, it is named after give way to, behind, near. If a hold never clears, report it with the callsign and the reason shown; see Bug reports and feature requests.