CDI Course Needle Inop on GPS Setting

[Rivermoney]

Garmin CDI course needle went inop when Garmin 430 was set to GPS during flight. Cycled GPS and CDI passed startup test. CDI course needle stayed centered - setting course to a nearby 'direct to' did nothing. Selected VLOC with nearby VOR and CDI course needle functioned normally. Appreciate any ideas. 

[Schinderhannes]

The switching between GPS and VLOC is internally in the GNS430. Considering that the needle works in VLOC mode I would start with checking the GNS430. What did the internal CDI show?

[Rivermoney]

Thanks - I am not sure what you mean when you ask 'what did the internal CDI show?' If mean did the 430 display the the course, DTK, etc., then yes. The 430 display provided all normal functions and display. Now, I will say when I landed and cycled the 430 on and off, then set a nearby intersection, the msg function did not flash and I did not see a 'course to' provided. I usually see that when on the ground so I can adjust the course in the CDI. 

[Ragsf15e]

13 hours ago, Wreindollar said:

Thanks - I am not sure what you mean when you ask 'what did the internal CDI show?' If mean did the 430 display the the course, DTK, etc., then yes. The 430 display provided all normal functions and display. Now, I will say when I landed and cycled the 430 on and off, then set a nearby intersection, the msg function did not flash and I did not see a 'course to' provided. I usually see that when on the ground so I can adjust the course in the CDI. 

Maybe he means the cdi you can display on the 430?  Left most page of the Nav “chapter”.  Ie, one click left on the right side small knob from the map page.  There should be a cdi on the upper half of the screen.

[Rivermoney]

Great point. Thanks. I am going to remove the GPS and reseat in the tray (never can hurt) and do some ops check including full CDI test (versus just looking at the flags/half up/left) from the second GPS430 power up test screen. I will then cycle over to the first screen - totally forgot about that. I suspect that will confirm any GPS unit issue provided the first reply is correct that the GPS/VLOC switching is in the unit which does make sense. I have already talked to Garmin Service about a repair...not ready to upgrade yet. I do fly mostly IFR filings and find the 430 has what I need for the next few years. Thanks again.

[Rivermoney]

R&R the 430, pins looked good. Powered up the unit and reviewed CDI test, flags and needles in CDI equaled the 430 test functions (half up, half left, no flags, etc), rotated the CDI OBS knob to N-S-E-W and headings showed correct in 430. Set a Direct to in the 430, msg indicator blinked, pushed msg and got the course, set course in CDI and course needle remained centered. CDI needles remained centered now with no movement other than when 430 powers up. When 430 is on first Nav selection the CDI graphic on the 430 screen displays course and the 'graphic needle' is centered. So, guess I will be sending 430 in for repair. 

[kortopates]

10 minutes ago, Wreindollar said:

Set a Direct to in the 430, msg indicator blinked, pushed msg and got the course, set course in CDI and course needle remained centered.

Of course it remains centered - sorry don't mean to sound flippant but this doesn't describe a GPS error. Whenever you push the direct key, you are re-centering the GPS CDI. Only if you moved since an earlier Direct key entry to the same waypoint will the DTK change - but the CDI will be centered - both on the GNS Default Nav display as well as the CDI. Important - just like on an ILS in LOC mode, when in GPS mode, turning the OBS has NO effect on the CDI (you be trying to change the DTK). But as soon as you enter OBS mode (in GPS mode) now you can change the DTK by turning the OBS knob on your CDI and you'll see it deflect.

 

On 5/10/2021 at 6:08 PM, Wreindollar said:

CDI course needle stayed centered - setting course to a nearby 'direct to' did nothing.

Ditto here from your first post.

Both of these show the GPS is working as expected. 

The good news is so far this is all normal and expected behaviour. If you have a real problem, its not explained here yet.

Edited May 13, 2021 by kortopates

[Ragsf15e]

@kortopates nailed it, but let me try to give you a clear test... use direct to in gps mode to something say 20nm away.  CDI WILL CENTER.  Now press OBS button on the bottom of the 430. Turn OBS knob on hsi and you should see the CDI deflected left or right as you change the desired OBS course.  If you fail to push the OBS button on the unit, you can turn the obs knob all you want and the needle will stay centered.

[Rivermoney]

Thanks all. I did the actions above. 430 start test was fine. Selected Direct and pressed OBS and rotated OBS on CDI and it did deflect. So I will go fly tomorrow and monitor the CDI to see if I get the same error that caused me to review this. The original cause for concern was while flying the CDI course needle was left of center and stayed left of center even no matter what lateral aircraft movements were made to get back on course. Even when direct was selected the needle stayed left of center. Upon reading my original post I did not detail that experience only the ground check when I got to the destination. 

[jaylw314]

23 minutes ago, Wreindollar said:

Thanks all. I did the actions above. 430 start test was fine. Selected Direct and pressed OBS and rotated OBS on CDI and it did deflect. So I will go fly tomorrow and monitor the CDI to see if I get the same error that caused me to review this. The original cause for concern was while flying the CDI course needle was left of center and stayed left of center even no matter what lateral aircraft movements were made to get back on course. Even when direct was selected the needle stayed left of center. Upon reading my original post I did not detail that experience only the ground check when I got to the destination. 

Hope I'm not stating the obvious, but make sure you were pressing Direct-ENT-ENT rather than Direct-Direct-ENT  wouldn't be the first time someone made that mistake!

[Rivermoney]

Direct, select identifier, enter, then enter to activate. The detailed cause was we were returning to home base with two legs remaining on the 430's FPL - EMI and KGAI (home field). Approaching EMI I was cleared direct to KGAI. I 'cleared' EMI from the 430 flight plan and adjusted the CDI course to the 430's DTK. The CDI After a few minutes I noticed no CDI movement during my scan. The CDI appeared to always be left of center. With the airfield in sight I cancelled IFR then made a few turns but no needle movement was noticed (I was 7 miles from field). At that point I did Direct, KGAI, enter, enter. The CDI stayed in the same position. Once on the ground I powered down the 430 and powered back up. I will fly tomorrow and observe. I am in the DC area and have experienced some anomalies over time..,recently a Loss of Integrity but that I isolated to potential interference from the adjacent rack mounted back up nav/com which I was using to cross check ILS approach fixes. 

[jaylw314]

There's also the possibility of a sticking CDI needle, although that would generally happen on the ground more often than in the air (fewer vibrations to shake it loose)...

[Rivermoney]

Sorry - former Marine Corps pilot...I did give it the proper avionics 'realignment' and 'tuning' adjustment via my hand in an attempt to coax it back to full function...