Route tracking (en-route next fix)¶
Available now.
What it does¶
Once airborne and past the initial climb, the engine keeps a live route -- the filed route's fixes, plus the assigned STAR's own transition, common route and runway-transition fixes once a descent plan exists -- and tracks which fix on it the aircraft is heading for right now, the same way a real controller keeps track of where an aircraft is along its route rather than just its raw position.
This is what drives:
- The Route map card on the radio panel, showing the filed fixes with the one you're tracking highlighted (with its distance), anything already behind you dimmed, and a line from the aircraft to that next fix.
- Direct-to validation and "is behind you" denials.
- Departure's choice of which fix to clear you direct to at radar contact.
- Automatically turning a radar-vectored aircraft back onto its route.
- The off-course check below.
How a fix gets marked passed¶
A fix counts as passed once the aircraft comes within 2 nm of it, or once it's abeam the fix -- past it along the leg from the previous fix, even if the aircraft never actually flew directly over it (a fix well off to one side of a wide turn shouldn't stay "next" forever). Several fixes can pass in a single check if the aircraft skipped past more than one -- flying a shortcut, or a vector that rejoined the route well ahead of where it left it.
A direct-to makes the requested fix next and drops everything before it from consideration; the current leg then starts from wherever the aircraft was at the moment the direct-to was issued, not from the previously-tracked leg start -- otherwise a direct-to given well off to one side of the old leg would read as instantly far off course.
Turning a vector back onto the route¶
When Tower assigns a takeoff heading for radar vectors, or Approach/Center otherwise puts the aircraft on a heading, the route keeps tracking in the background but the off-course check (below) stands down while a heading is actually assigned. After the aircraft has been on that heading for 2 minutes -- and only while still navigating toward the route via Departure or Center (not while Approach is actively vectoring for the approach itself, and not with a handoff or a readback still pending) -- the controller currently working the aircraft clears it direct to the next fix on its own:
"...proceed direct Battle Ground"
This is read back like any other direct-to.
Off-course monitoring¶
xatc.atc.route_track.OffCourseMonitor checks the aircraft's distance off the current
leg (the previous fix to the next fix) -- but only while it's actually supposed to be
navigating that leg itself: never while on an assigned heading (a vector), and never
right after an approved deviation that hasn't
yet been resumed. The tolerance scales with conformance strictness:
| Strictness | Off-course tolerance | Sustained before it fires |
|---|---|---|
| Relaxed | 5 nm | 60 s |
| Normal (default) | 3 nm | 30 s |
| Checkride | 2 nm | 20 s |
Once it fires: "you appear to be off course, proceed direct Battle Ground", escalating straight to "possible pilot deviation" if it isn't corrected. The escalation resets on a handoff -- a controller that's just handed you off to the next one never gets to say "possible pilot deviation" after the fact, since it's no longer the one working you.
Cleared direct a fix, the check is different: cross-track distance from a line doesn't mean much once you're flying straight at a point rather than along a leg, so instead it's whether your ground track actually points at the fix (within 30°) and your range to it isn't growing -- after a minute's grace to actually turn onto it. A direct-to issued at radar contact, or answering a heading question, anchors the next leg where the aircraft is at that moment, so it isn't judged against a line drawn from somewhere else entirely once it resumes its own navigation.
Configuration¶
None -- route tracking follows directly from the filed flight plan and, once assigned, the destination's STAR.
Limitations¶
- A route fix with no matching position in the loaded nav data is skipped with a warning rather than blocking the whole route.
- The map card and next-fix tracking only run once airborne past the initial departure
climb (
DEPARTURE,ENROUTE,DESCENT) -- there's no route view while still on the ground or in the initial takeoff phase.