Amadeus

Amadeus

Well Known Member
My RV-12iS has the dual G3X VFR package that has had the GPS20A removed and replaced with the GPS175 in March 2023. Last fall, shortly after a take off in VFR conditions, the G3X map screen and PFD background displayed in the color red and the audio alert of "terrain, terrain, pull up, pull up" began repeating itself. Having flown from that airport multiple times and also being able to see clearly on a CAVU day I knew there was nothing in my path at my altitude and continued my flight. Once at cruising altitude my pilot/passenger and I began to assess why this may have occurred and came up with a WAG (wild assumption guess). We were attending a fly-in event that had many aircraft departing once festivities were over. I had just started up and the GPS175 was still in TERR TEST mode when the marshaller began directing me to pull into the line of traffic moving toward the runway. My temperatures were in the green so I began movement. We both figured that moving the airplane while the TERR TEST was still being conducted confused the navigator as to actual location so I made mental note to always wait for the test to complete before beginning to taxi.

Waiting for TERR TEST to complete before movement seemed to do the trick for quite a few months. Then in March of this year I was departing another familiar airport on a VFR day when the same "terrain, terrain, pull up, pull up" event again occurred despite waiting. I wrote it off as a one time thing before it once again occurred leaving an unfamiliar airport (but in a very flat farmland area on the Illinois/Indiana state line) in the path of totality for the April 8 eclipse. Because this was once again taking off from an event when everyone else was I wondered if the close proximity to other navigators could have an input to the problem; after all, two of the three data points are leaving crowded events. However it happened again just last weekend at a small uncrowded airport.

Fortunately all these occurrences were in VFR conditions. Until I figure it out I will not be taking off into IFR conditions. Has anyone else experienced this navigator behavior? I'm stumped on where to begin my research.
 
Your alert audio will be coming from one of your GDU displays, not your IFR navigator.

You can adjust the sensitivity of terrain alerts using the menu options on the Terrain page; they default to the most sensitive settings.
 
mburch said:
Your alert audio will be coming from one of your GDU displays, not your IFR navigator.

You can adjust the sensitivity of terrain alerts using the menu options on the Terrain page; they default to the most sensitive settings.
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Thank you, I will look at those setting options.

The GDU displays are receiving GPS data externally (the GPS175). Would this have any bearing on perhaps stemming from the navigator unit?
 
mburch said:
They will use their own GPS data for terrain alerting, unless something is amiss with your GPS installation.
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Perhaps something is amiss. I do get the "message" on the GDU that "GPS is from an external source" once everything is powered up and operating.
 
Amadeus said:
Perhaps something is amiss. I do get the "message" on the GDU that "GPS is from an external source" once everything is powered up and operating.
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Yes, this is indicative of a problem with the GPS receiver, antenna, or reception to your GDU displays. I would address this before further flight as it is not a normal condition.
 
Walt said:
Huh? The G3X requires a GPS antenna and the GPS175 requires its own antenna, neither has a built in antenna.
Perhaps a review of the associated manuals would help you.
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It isn't built in to the GDU. THIS is the antenna.
 
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I see that I can choose between "external" and "internal" antenna in the G3X settings. Once the GPS175 is booted up and running I get the message on the G3X GDU that the GPS source is from the "external" antenna (meaning the GPS175). If I just click MENU and select INTERNAL as the GPS source would this solve the issue or would it mean that the G3X is now ignoring the GPS175 for everything including the flight plan, approach, etc.?
 
Amadeus said:
I see that I can choose between "external" and "internal" antenna in the G3X settings. Once the GPS175 is booted up and running I get the message on the G3X GDU that the GPS source is from the "external" antenna (meaning the GPS175). If I just click MENU and select INTERNAL as the GPS source would this solve the issue or would it mean that the G3X is now ignoring the GPS175 for everything including the flight plan, approach, etc.?
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Don't confuse GPS navigation with GPS reception. The setting you are looking at affects the flight plan only, not the GDU's GPS receiver. Ignore this and focus on the issues with your GDU's GPS reception. Make sure the GPS antenna configuration is correct, and make sure your GDU can achieve a valid GPS fix. If you don't know how to do this, Garmin product support can help you.
 
I get the alert when I'm going into a local, private, grass strip. It is very annoying and I can't understand why my GTN 650xi doesn't understand it is an airport.
 
Hangar 1271 said:
I get the alert when I'm going into a local, private, grass strip. It is very annoying and I can't understand why my GTN 650xi doesn't understand it is an airport.
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Terain alerts are generated by the G3X (I believe) and have nothing to do with the GTN or it’s databases…..
 
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