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Failure of GAD-29 or GMU-11 in a garmin system

prkaye

Well Known Member
I'm just thinking through and documenting different possible failure modes for my new (IFR) setup. I have a Dual G5 system with a GPS-175 and a GNC-255 Nav/Com, all connected via a GAD-29 interface and a GMU-11 magnetometer.
Am i correct in assuming that if either the GAD-29 or the GMU-11 fail, then the G5 units will no longer be able to function as an HSI for the GPS or the Nav/Com? In this case, it seems to me my failover would be to navigate using the GPS-175's integrated display for a non-precision approach. Does this sound right?
 
I'm just thinking through and documenting different possible failure modes for my new (IFR) setup. I have a Dual G5 system with a GPS-175 and a GNC-255 Nav/Com, all connected via a GAD-29 interface and a GMU-11 magnetometer.
Am i correct in assuming that if either the GAD-29 or the GMU-11 fail, then the G5 units will no longer be able to function as an HSI for the GPS or the Nav/Com? In this case, it seems to me my failover would be to navigate using the GPS-175's integrated display for a non-precision approach. Does this sound right?
Phil,

Losing the GMU 11 magnetometer has little impact to the operation of the system. The G5 HSI reverts to using GPS track, so the HSI functionality is preserved.

Some feel that a GPS track based HSI is far superior to a heading based HSI. I have no interest in knowing what direction the aircraft nose is pointing (heading), but care a lot about whether or not the aircraft ground track equals desired track (course). With a GPS track based HSI, the HSI course pointer is always pointing straight up when the CDI is centered and the aircraft is on course to the next waypoint regardless of the direction and magnitude of winds aloft.

Since the MapMX RS-232 output of the GPS 175 is connected to both G5 units, even if you lose the GAD 29, you retain GPS lateral navigation capability (shown on both the HSI and PFD G5 displays) for whatever flight plan or procedure is active in the GPS 175.

If you lose the GAD 29, you do lose GNC 255 navigation capability since it is only connected to the GAD 29.

Steve

View attachment G5 to GPS175 Wiring.pdf
 
Thanks Steve! This is really helpful, and it also elevates my confidence in this system.

Phil,

Losing the GMU 11 magnetometer has little impact to the operation of the system. The G5 HSI reverts to using GPS track, so the HSI functionality is preserved.

Some feel that a GPS track based HSI is far superior to a heading based HSI. I have no interest in knowing what direction the aircraft nose is pointing (heading), but care a lot about whether or not the aircraft ground track equals desired track (course). With a GPS track based HSI, the HSI course pointer is always pointing straight up when the CDI is centered and the aircraft is on course to the next waypoint regardless of the direction and magnitude of winds aloft.

Since the MapMX RS-232 output of the GPS 175 is connected to both G5 units, even if you lose the GAD 29, you retain GPS lateral navigation capability (shown on both the HSI and PFD G5 displays) for whatever flight plan or procedure is active in the GPS 175.

If you lose the GAD 29, you do lose GNC 255 navigation capability since it is only connected to the GAD 29.

Steve

View attachment 31117
 
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