Flight Plans

nav.Plan builds an IFR flight plan from what the rest of the library already knows: the airports’ layouts and procedures (pkg/airport), the weather and runway in use, and the airway graph. The plan can be printed, saved as JSON, or written as an MSFS .pln file.

import "github.com/mrlm-net/simconnect/pkg/nav"

Planning a flight

wx := nav.StaticWeather(240, 10, 9999, 15, 5, 1013) // or from nav.WeatherReader
fp, err := nav.Plan(nav.FlightPlanRequest{
    Departure:  nav.AirportInfo{ICAO: "LKPR", Layout: lkpr, Procedures: lkprProcs},
    Arrival:    nav.AirportInfo{ICAO: "LOWW", Layout: loww, Procedures: lowwProcs},
    Type:       "A20N",
    DepWeather: &wx,
    DepLimits:  nav.RunwayLimits{Preferred: []string{"24", "06"}},
}, graph)
if err != nil {
    return err
}
fmt.Print(fp)
pln, _ := fp.PLN()
os.WriteFile("LKPRLOWW.pln", pln, 0o644)

Layouts come from airport.Loader, procedures from airport.ProcedureLoader, the graph from nav.LoadAirwayGraph (a crawl saved by examples/spike-airways). The examples/flight-plan command loads everything from the simulator:

go run ./examples/flight-plan -from LKPR -to LOWW -type A20N -out LKPRLOWW.pln

LKPR/24 → LOWW/16  A20N  FL270  160 NM  ETE 0:30  track 138°M
route: VOZ5M VOZ M725 LANUX LANU7W
approach: ILS 16
fuel kg: taxi 150  trip 1330  contingency 67  alternate 0  reserve 1100  block 2647
  RW24     SID                   0.0 NM   1175 ft
  *        SID       VOZ5M       3.7 NM   2813 ft  ≥1700
  PR411    SID       VOZ5M      11.2 NM   6100 ft
  PR412    SID       VOZ5M      34.9 NM  16511 ft
  VOZ      SID       VOZ5M      47.3 NM  21992 ft
  TOC      ENROUTE              58.7 NM  27000 ft
  TABEM    ENROUTE   M725       69.3 NM  27000 ft
  TOD      ENROUTE              88.8 NM  27000 ft
  OKF      ENROUTE   M725       90.1 NM  26491 ft
  LANUX    STAR      M725       95.7 NM  15000 ft  6000–15000
  NERDU    STAR      LANU7W    126.8 NM  12847 ft  ≥6000
  WW671    APPROACH  ILS 16    143.0 NM   6798 ft  ≥5000
  FI16     APPROACH  ILS 16    145.1 NM   6039 ft  ≥5000
  RW16     APPROACH  ILS 16    159.7 NM    647 ft  600

How the plan is made

1. Runways. DepartureRunway / ArrivalRunway when set, else ActiveRunways for the airport’s weather (DepWeather, ArrWeather) and limits (DepLimits, ArrLimits). Without weather the wind is calm, so the longest runway (or the first preferred one) wins.
2. Procedures. Every SID from the departure runway (with each enroute transition) is resolved from the departure end of the runway, and every STAR to the arrival runway is joined to the best approach (airport.Procedures.BestApproach: ILS, then RNAV…) through the approach transition that starts where the STAR ends. Plan takes the pair with the shortest path: SID + great circle from the SID’s last fix to the STAR’s first + STAR and approach. Without STARs, the approach is entered through the transition that fits best, or at its final.
3. Enroute. Between the SID and the STAR the route follows the airway graph (RouteOrDirect); when the airways are more than EnrouteMaxStretch (1.5) times the direct distance — common around a TMA — it flies direct. An airport without procedures joins the airways at the nearest fix within 50 NM toward the other airport, direct from its runway threshold (or its position without a layout).
4. Cruise level. CruiseLevel applies the semicircular rule (RVSM) to the magnetic track between the airports: odd levels (FL350, FL370) on 000–179°, even (FL340, FL360) on 180–359°. It takes the highest such level up to the type’s MaxFL at which the climb and descent (from the rates and speeds in Performance) leave at least 15% of the distance level, and at least 2000 ft above the higher airport. Set CruiseFL to force a level.
5. Profile. Every waypoint gets its distance from the start and a planned altitude: a straight climb to the top of climb, level, a straight descent from the top of descent, kept within the waypoint’s constraints. TOC and TOD are inserted as waypoints of kind PointProfile.
6. Time and fuel. ETE is the climb, cruise and descent at the type’s speeds, without wind. Trip fuel is the cruise fuel flow over that time plus half as much again during the climb; contingency is 5% of it, the final reserve 30 minutes at the cruise flow, the alternate AlternateFuelKg, and the block adds taxi fuel.

The magnetic variation comes from the departure’s procedures (Procedures.MagVar), else the arrival’s, else it is 0.

Waypoints

FlightPlan.Waypoints runs from the departure runway threshold (or airport) to the arrival threshold (or airport). Each point has a Phase (SID, ENROUTE, STAR, APPROACH) and the Airway it is reached by: an airway name, DCT, the SID or STAR name, or the approach name. Constraints are in feet (AltMinFt, AltMaxFt, both set and equal for an “at”) and knots (SpeedMaxKts); Constraint() formats them as charts do. Computed points of the procedures (the end of a climb, a heading to radar vectors) have no ident.

PositionAt(distNM) gives the position, planned altitude and track at a distance along the plan. The Traffic Manager uses it to make an aircraft appear en route, where its flight would be by then.

Route is the ICAO route (item 15): the SID and its last fix, then airway and fix at each change of airway, the STAR’s first fix and the STAR — VOZ5M VOZ M725 LANUX LANU7W, or DCT FOLWU L984 SULUS Z650 TONSU Z35 LOMKI LOMK8T from an airport without procedures.

The .pln file

PLN() writes the MSFS flight plan format (SimBase.Document, AceXML version 1,1):

• header: Title, FPType IFR, RouteType (HighAlt from FL180, else LowAlt), CruisingAlt, departure and destination ID, position (DepartureLLA, DestinationLLA) and name, DeparturePosition (the runway), AppVersion;
• one ATCWaypoint for the departure airport, each charted fix, and the destination airport. SID fixes carry DepartureFP and RunwayNumberFP (with RunwayDesignatorFP for L/R/C), STAR fixes ArrivalFP, approach fixes ApproachTypeFP (ILS, RNAV, VORDME…) and the runway, enroute fixes their ATCAirway. Every fix has its ICAORegion and ICAOIdent;
• positions in the .pln format with the planned altitude: N50° 6' 3.13",E14° 15' 36.23",+001247.00 (FormatLLA).

Runway thresholds, computed points and TOC/TOD are left out: the simulator rebuilds the procedures from their names.

Performance

PerformanceFor knows A20N, A320, A321, B738, B38M, B77W, B789, E190, CRJ9, AT76 and DH8D; other types plan as a generic medium jet (Performance.Type is then empty). The figures are typical round numbers, not a particular airframe’s.

Limits

• No winds aloft: ETE and fuel are for still air.
• The profile is straight lines between TOC and TOD; constraints only clamp the planned altitude at their own waypoint.
• The airway graph covers the crawl radius around its centre (250 NM around LKPR in the test data); further out the route is direct.
• The weather from WeatherReader is at the user aircraft, so it is right for the departure only; give the arrival its runway or weather yourself.