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Loop Route on ND (v1.10)


Scotflieger

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I hope I'm not the first person to break v1.10.

When approaching a turning point flying level at FL120 I pressed the ALT knob to engage ALT Managed mode. At this point the route on the ND which had been showing a left turn at the GOSAM waypoint, changed to a loop to right starting with a reverse right turn. The route anomaly remained in both ARC and NAV mode. The aircraft started to fly the wrong route until it came close to the turning point then routed to the next waypoint correctly.

A319NDLoop.jpg

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It was a flight test route I use out of Edinburgh comprising a linked SID and STAR. Using latest NavDataPro 16OCT12NOV/14 (installed because I was unable to unzip early error with 1.10).

EGPH RWY 24 - SID GOSA1C 635 UW ITH95 ITH14 MAVIX GOSAN - STAR TWEE2A MARGO INPIP INREV ESKDO 10TLA TARTN TWEED ITH90 ITH 40 EGPH ILS24 - max FL220

All F-PLN DISCONTINUITY lines cleared.

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Another example for your collection. Climbing out of EGPH on SID GOSA1C (SID GOSA1C 635 UW ITH95 ITH14 MAVIX GOSAN) I had to change to HDG set mode. On selecting DIRECT steer to ITH14 a complete 360 deg loop was drawn on the ND.

post-103067-0-07109400-1413819247.jpg

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It started to follow the loop but as it passed close to the waypoint (ITH14) the Nav system switched to the following waypoint (MAVIX) and returned to the planned route.

Sent from my iPad using Tapatalk

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  • Aerosoft

It started to follow the loop but as it passed close to the waypoint (ITH14) the Nav system switched to the following waypoint (MAVIX) and returned to the planned route.

Sent from my iPad using Tapatalk

You know the real bus does the same?

Often it starts on the incorrect path but then decides it is silly and flies the right route.

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I believe it is the proximity condition to the waypoint that is deciding to select the next waypoint that sorted out the route. However, as a previous specifier and designer of navigation software, there appears to be a big anomaly in the model that is calculating the right hand loop to arrive at the waypoint rather than the direct or left radius turn onto the direct track between the next and following waypoints.

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Indeed. I have no personal knowledge of how the curves are plotted, but I imagine it should go something like this:

* Waypoints are plotted in spherical space. Great circle arcs (minimum distance path between two points on the surface of a sphere) are added to connect the waypoints.
* Circles no smaller than a predetermined minimum radius (corresponding to a 30-degree bank at the expected speed) are placed near each waypoint on the inside angle such that they lie tangent to (extensions of) these lines. The smallest feasible circle is selected.
* If two circles intersect each other between where they touch the straight-line path, a third circle is placed to be inside tangent to both circles. Repeat recursively as necessary.

In this manner, one can produce a smooth path in spherical geometry that minimizes both total length and total deviation from waypoints.

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