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I wish the article contained some explanation of why the processing for NATS requires looking at both the ADEXP waypoints and the ICAO4444 waypoints (not a crit
by dundarious 3y ago
I wish the article contained some explanation of why the processing for NATS requires looking at both the ADEXP waypoints and the ICAO4444 waypoints (not a criticism per se, it may not have been addressed in the underlying report). Just looking at the ADEXP seems sufficient for the UK segment logic.
I'm guessing it has something to do with how ICAO4444 is technically human readable, and how in some meaningful sense, pilots and ATC staff "prefer" it. e.g., maybe all ICAO4444 waypoints are "significant" to humans (like international airports), whereas ADEXP waypoints are often "insignificant" (local airports, or even locations without any runway at all).
Of course with 20/20 hindsight, it seems obviously incorrect to loop through the ICAO4444 waypoints in their entirety, instead of "resuming" from an advanced position. But why look at them at all?
- masklinn 3y agoPossibly it needs the ICAO information to communicate with some systems, but has to work in ADEXP to have sufficient granularity (the essay mentions the possibility of “clipping”, a flight going through the UK between two ICAO waypoints).
- dundarious 3y agoYes, I'm essentially wanting to know more about those existing ICAO-based systems, be they machine or not.
- t0mas88 3y agoThey use the ADEXP to determine which part of the route is in the UK. Because the auto generated points are ATC area handover points. So this data is the best way so see which part of the route is within the UK airspace. Then it needs to find the ICAO part that corresponds, because the controller needs to use the ICAO plan that the pilot has. If the controller sees other (auto generated) waypoints that the pilots don't have you get problems during operation. A simple example is that controllers can tell pilots to fly in a straight line to a specific point on their filed route (and do so quite often). The pilot is expected to continue the filed route from that point onwards. They can also tell a pilot to fly direct to some random other point (this also happens but less often). The pilot is then not expected to pick up a route after that point. The radio instruction for both is exactly the same, the only difference is whether the point is part of the planned route or not. So the controller needs to see the exact same route as the pilots have, not one with additional waypoints added by the IFPS system.
- jameshh 3y agoThanks for this explanation. So, is the ICAO plan in some sense the "single source of truth", being the international standard and all?
- dundarious 3y agoYes, thanks, t0mas88. I have some more questions but I can feel myself drifting into the weeds a bit, and your comment was extremely helpful as-is.