INS losing track

[PilotGW]

Hi,

Slightly odd one. I've been doing a few practice departures and climbs up to cruise, getting a feel for the aircraft.

I departed from Luton (EGGW) and set course towards Menorca (LEMH) using the following route, the first 9 waypoints entered manually (not imported through Simbrief), starting at RODNI.

EGGW/25 N0480F350 RODN1B RODNI N27 ICTAM Q63 CPT UN859 SOPIL DCT BALAN DCT EVPOK DCT NARAK DCT GAI DCT LOMRA DCT ROCAN DCT GEANT N727 SARGO SARG5B LEMH/01

Upon passing GWC VOR (Waypoint 7 - N5051.3, W00045.4) The aircraft should have turned slightly left towards SITET (Waypoint 8 - N5006.0, E00000.0). Instead, it entered a right turn, almost as if it's trying to double back to GWC.

This happened a few days ago. I shrugged it off as user error, perhaps a bug.

I tried again today and the exact same thing happened at the exact same point. I managed to get it into heading mode to turn it back towards the next waypoint (SITET) but I noticed the distance to the next waypoint was increasing instead of decreasing. Clearly it hadn't sequenced properly. I had to do a manual track change from waypoint 7 to 8 to get it work properly.

Am I doing something wrong?

[RyanAlmeida95]

Interesting - with this does the INS show 78 as the correct leg and does the moveable map make sense to the waypoints that you've entered?.. just incase of input error (although you've proved it twice) 

Waypoint N5060.0E00000.0 is a good one because even if you get E/W mixed up it's the same location. So should be fairly safe from error.

However interesting that the distance is increasing with leg 78 would only indicate that it thinks the waypoint is somewhere else.

[PilotGW]

Just tried again but with a Simbrief import so there's no doubt over whether the coordinates were correct. Same thing happened. The INS gets stuck on 6 > 7, when it should change to 7 > 8.

Looks to be correctly positioned on the moving map display. It seems to get confused as soon as I fly over the waypoint. I get the sense the aircraft feels as if it's 'missed' GWC VOR and tries to have another go by turning back.

Approaching GWC. Leg 6 > 7. Correct coordinates and positioning on the map.

Aircraft turns right overhead GWC. INS stuck on leg 6 > 7. Distance starts increasing. Aircraft now off track according to the moving map.

[RyanAlmeida95]

I beleive you @PilotGW
Copied your plan and had the same thing.

 

[IniJamir]

I'll pass this along to the team, thank you.

[RyanAlmeida95]

Just to add to the above, after some further flying around in circles and testing out the waypoints - I think the INS sturggles or does not recognise changing to a waypoint when the LAT/LON is either N/S0000.0 or W/E00000.0. This may be because it thinks the LAT or LON has not been loaded yet.. 

How each waypoint starts out when not loaded (WPT8 in this example).


I changed the waypoint in the example above to N5006.0, E00000.1 and it worked by automatically changing to the next waypoint.


Hope that helps - I just can't quite find any data on that being a real world issue.. only thing close it something called null island issues.  

[RyanAlmeida95]

Also it will go from the last loaded waypoint back to WP1 if the remaining waypoints are left blank
In my case of flying arounn a hand full of waypoints, I left WP8 and 9 blank.. so it automatically switched from WP7 to WP1. 🙂