Traffic Manager

traffic.TrafficManager runs the schedule of the managed airports (#368). It decides what happens when. A Spawner does it in the simulator: it knows the stands, models, runways and controllers, and it reports back.

cfg := traffic.DefaultScheduleConfig()
mgr := traffic.NewTrafficManager(spawner, traffic.ManagerOptions{
    Source: func(from, to time.Time, airports []string) []traffic.Flight {
        return traffic.Schedule(cfg, traffic.ScheduleOptions{Focus: airports, Seed: seed ^ uint64(from.Unix()/3600)}, from, to)
    },
    Picture:     picture, // the TrafficPicture: other traffic is respected
    MaxAircraft: 12,
    OnEvent:     func(e traffic.ManagerEvent) { log.Println(e.Kind, e.Flight.Callsign, e.Reason) },
}, "LKPR")

for now := range time.Tick(time.Second) {
    mgr.Tick(now)
}

What it does

The limits are MaxAircraft in total (default 24) and MaxPerAirport (default 16). Spawns are spaced: arrivals ArrivalSpacing (3 min) apart, departures DepartureSpacing (1 min). The Source is asked Horizon (2 h) ahead, an hour at a time. Flights already too late when they are added are left out, so a schedule started mid-day does not show the morning as cancelled.

The Spawner

type Spawner interface {
    Spawn(f ManagedFlight)  // must not block: report with Update, Describe, Failed
    Remove(f ManagedFlight)
}

• Update(callsign, status, now) reports progress: boarding, taxiing, departing, departed, approaching, landed or parked.
• Describe(callsign, model, stand, runway) records what the Spawner chose, for the boards.
• Failed(callsign, err, now) handles a failed spawn. It is tried again after RetryAfter, up to MaxAttempts, and the Spawner takes another model or stand on each attempt (f.Attempts). An aircraft that was already flying is cancelled and removed.
• ErrSpawnBlocked means the place was taken: another aircraft is at the STAR entry, or no stand is free. The spawn waits and is tried again without counting an attempt.
• A Spawner that is also a Holder (Hold(f, on)) can keep a boarding departure on its stand. The map uses TaxiController.HoldPushback.

ModelsFor(models, airline, name, type, max) ranks the simulator’s aircraft titles for a flight:

1. The type in the airline’s livery (FSLTL_FAIB_B738_TVS-Smartwings, FSLTL A20N DLH Lufthansa).
2. Another type of the same size in the airline’s livery, same maker first.
3. The type in any livery.

Within each of the first two, titles with the airline’s ICAO code come before those that only carry its name, which may be a sister airline’s (“TVP-Smartwings Poland” for Smartwings, TVS). Stubs, VIP, business-jet, freighter and military versions are left out.

ModelsForFlight(models, airline, name, type, callsign, max) ranks the same way, but takes the equally good best titles in turn by call sign. Each flight always gets the same one, and a fleet with several liveries or versions installed shows them all instead of one aircraft. The map spawns with it.

Situation checks

Each Tick the manager looks at each airport the way the people there would. It predicts what is coming and adjusts. The controllers already do this up close (give way, queue behind, hold for traffic behind the stand); the checks cover the wider picture. A check is a function func(Situation) []Advice. ManagerOptions.Checks defaults to DefaultChecks():

The advice actions are:

• AdviceDelay delays a spawn.
• AdviceHold holds a departure on its stand while it is advised; the hold is released on the first Tick that no check advises it.
• AdviceEstimate sets Estimated, shown on the boards with Note.
• AdviceRemove removes the aircraft.

Write your own checks and add them with append(traffic.DefaultChecks(), myCheck).

Other traffic

ManagerOptions.Picture gives the manager the traffic picture. Aircraft that are not ours count as other traffic: MSFS AI, other add-ons and the user. The manager can treat it two ways:

• OtherRespect (the default): other traffic fills the taxiways, takes landing slots and, through the Spawner, blocks spawn points. Situation.Others lists it for your own checks, and Others(icao) lists it for the app.
• OtherIgnore: the manager plans as if it were not there.

Switch between them with SetOthers.

Enroute traffic and overflights

Traffic flies between airports, not only at one (#369).

• Enroute arrivals: an arrival appears EnrouteLead (20 min) before it would appear at its STAR entry. It shows up en route on its flight plan, at the point the plan puts it now, at the planned level. MSFS AI flies it to the entry, where the Spawner hands it over to the arrival controller (status enroute, then approaching). If the enroute spawn fails, the arrival appears at its STAR entry instead, with no attempt lost. A negative EnrouteLead turns enroute arrivals off.
• Overflights: ManagerOptions.Overflights gives flights between airports outside the area whose route crosses it. traffic.Overflights(cfg, OverflightOptions{Centre, RadiusNM, PerHour, Density, Seed, Exclude}, from, to) generates them: airports outside the area, an airline serving both ends, a type that fits, and Enter/Exit when the flight crosses into and out of the area. Each appears at Enter, where its flight is by then, up to MaxOverflights (4) at once.
• Departures fly on after their SID along their plan, and stay ours.
• Leaving: an airborne aircraft of ours (departed, en route, overflying) is removed once the picture has not seen it for LeftAfter (1 min), i.e. it left the area. RemoveDepartedAfter (30 min) and an overflight’s Exit are the fallbacks.

Attach(callsign, objectID) tells the manager which aircraft flies a flight, so that it can follow it in the picture.

Appearing airborne

traffic.EnrouteStart(route []RoutePoint) turns the rest of a flight (points with altitude and speed, EnrouteSpeedKts) into two things:

• where the aircraft appears: at the first point, heading for the second, at its altitude and speed;
• the waypoint chain it flies from there.

Create the aircraft with Fleet.RequestNonATC at that position, then ReleaseControl and SetWaypoints once it exists. nav.FlightPlan.PositionAt(distNM) gives the point, planned altitude and track along a plan.

A flight plan cannot start an aircraft mid-route in MSFS 2024. AICreateEnrouteATCAircraft puts it on the ground at the plan’s departure airport whatever the phase. It also refuses a plan whose departure airport the simulator has not loaded.

Lifecycle events

Every step is an event, for the app’s own state machine: logs, boards, sounds, or rules of its own.

• ManagerOptions.OnEvent is called with each event, in order, outside the manager’s lock, so it may call the manager.
• Events() is a channel of 256 events; events are dropped when it is full.

Boards

Board(icao) returns an airport’s departures and arrivals by time. Each ManagedFlight carries its status, Estimated, Note (held, landing flow, late inbound), TurnFrom/TurnTo, the model, stand and runway, and Err when it was cancelled.

On the airport map

The Schedule section has Scheduled traffic: ▶ Start / ■ Stop, density and max aircraft, the airports whose timetables run (the loaded one by default; others are loaded on start), and the Departures, Arrivals and Overflights boards, with a board per managed airport (#371).

The spawner for scheduled flights (enroute arrivals and overflights appear airborne, see above; their labels show call sign, flight level and destination, and Overflights is a third board):

• picks a model in the airline’s livery (ModelsFor);
• plans the flight to or from the other end (SID, airways, level), or falls back to the runway’s SID or STAR;
• uses the runway in use, a free stand, a tug and automatic de-icing.

Other traffic is a layer in the Map section (Other traffic), drawn in blue. It is off by default and listed apart from ours. There you can set whether the schedule respects or ignores it, and ✕ removes one of those aircraft from the simulator.

The API:

• GET /api/schedule returns the settings and every flight.
• POST /api/schedule takes {"enabled", "airports": ["LKPR", "LKTB"] (or "icao"), "density", "maxAircraft", "seed", "others": "respect"|"ignore"}.
• GET /api/boards?icao= returns an airport’s departures and arrivals.
• POST /api/world/remove {"objectId"} removes an aircraft that is not ours.