HSI: CDI does not work correctly

[MoppleTheWhale42]

Since several weeks, the CDI does not always work correctly, when steer point is selected as reference. Sometimes the needle sticks to the edge of the HSI.

The attached screenshot shows the issue. I am flying heading 180 and the steer point is a little to the right of me. As I have set the course to 180, the CDI should indicate that the course is a little to the right. However, the CDI sticks to the very left of the HSI.

I have added a track, depicting the issue. What may be a bit special, is the high number of initial point objects in the mission.

HsiIssue.trk

[ASAP]

It does look strange just looking at the pictures. What’s lacking here is a picture of your CDU. How do you have the waypoint set up (to from, to to, etc) If you spin the Course needle can you get it to straighten up? Also go into the cdu and check the precision for the navigation. It could be that it is set to terminal and there is a very small window you have to be in to get the needle off the rail. 

Edited April 15, 2023 by ASAP

[MoppleTheWhale42]

The mission does not contain any flight plan. All waypoints have been set up in the ME as an initial points. Looking into the CDU, I see that it is set as FROM: 86.

I can turn the course all 360 degrees. The CDI needle does not move at all.

The precision is looking good. The CDU reports a FOM of 1 for INS, EGI, and BLD.

 

 

[jaylw314]

That's very odd.  All the waypoints above 1 are set with the attributes of TO-TO navigation in your mission:

nullWaypoint 1, however is set as TO-FROM.  That means your CRS needle determines the course heading for waypoint 1 when you start, but not any of the other waypoints.

I tested out making a new mission in Mission Editor, and even if you set them as TO-TO in ME, the custom waypoints and the landmark waypoints all show up as TO-FROM.  I assume the ME sets the attributes for the flight plan waypoints, not the mission waypoints.

So it's unclear to me how you ended up with a mission where all the mission waypoints are set as TO-TO

 

[MoppleTheWhale42]

The initial point handling in ME looks odd to me. The waypoints generated from the initial points seem to be in an arbitrary order in the CDU. They are neither sorted according to e.g. their names, or by the time they were added to the mission. I recently added four more initial points. They showed up in pairs of two, somewhere in the list of waypoints.

Can you explain why the TO/FROM setting of a waypoint affects the way the CDI works? To my understanding, the CDI should give me the indication towards a waypoint independent of any other waypoint.
 

 

[jaylw314]

8 hours ago, MoppleTheWhale42 said:

The initial point handling in ME looks odd to me. The waypoints generated from the initial points seem to be in an arbitrary order in the CDU. They are neither sorted according to e.g. their names, or by the time they were added to the mission. I recently added four more initial points. They showed up in pairs of two, somewhere in the list of waypoints.

Can you explain why the TO/FROM setting of a waypoint affects the way the CDI works? To my understanding, the CDI should give me the indication towards a waypoint independent of any other waypoint.
 

 

Waypoints 51+ are supposed to be system waypoints for local airports in the database, based on the ones in the DIVERT page.  They're not editable in the ME AFAIK.

The verbiage of waypoint attributes is super confusing, but if you have ever used the GNS530 in MSFS, it might make more sense:

• TO-FROM: works like a VOR/TAC, CDI shows deviation from radial from steerpoint set by CRS arrow
• TO-TO: works like flight plan navigation, CDI shows deviation from ground path between steerpoint and another waypoint regardless of CRS arrow
• DIRECT: works like Direct-to navigation,  CDI shows deviation from path between steerpoint and aircraft location when DIRECT selected, regardless of CRS arrow
• SCS: like nothing I've ever seen, CDI shows deviation from radial selected by CRS arrow from aircraft location when selected, regardless of steerpoint

I don't know where the terms TO-FROM and TO-TO come from, it's hard to make any sense of them.  I think of them as 'radial' and 'magenta line' navigation.

Additionally, to add confusion, every waypoint has one of the steering attributes above, but every flight plan can set a different attribute for that waypoint when used.  IIRC, flight plan attributes default to TO-TO (which makes sense). 

All my missions' waypoints 51+ have attributes of TO-FROM, so I don't know how yours became TO-TO.

Edited April 17, 2023 by jaylw314