I need some G1000 avionics support in the Phoenix area

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CFIDave
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Re: I need some G1000 avionics support in the Phoenix area

Post by CFIDave »

Boatguy wrote: Mon Oct 25, 2021 3:54 amYou are probably correct that it's an RF problem, but it may not affect all DA40/42s because there is a difference in the Faraday cages around the G1000. My understanding is that older DA40's have a very different box than the newer planes.
That's correct. Lycoming DA40s with legacy G1000 have an open rack in the back under the rear baggage compartment. In contrast, DA40NGs and DA42s have a metal "HIRF Box" surrounding the G1000 equipment rack that requires additional disassembly to access the LRUs contained within the rack.
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MarkA
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Re: I need some G1000 avionics support in the Phoenix area

Post by MarkA »

I have no easy way to confirm this but based on my experience developing RFID-based tracking systems, I suspect the RF interference is more likely coming through the GPS antenna/cables rather than the G1000 card cage.

Even in legacy G1000 systems, there's quite a bit a metal around the card cage and each of the individual GIA63W modules is also fully enclosed in metal. This will tend to shield those modules from most external RF as well as preventing them from generating RF interference of their own.

The GPS antenna and cables on the other hand are directly above the pilot and passenger's heads so the suspect transmitting phones were only a couple of feet directly below the antennas. Also, cell phones regulate their transmission power (the amount of RF interference they would create) based on how far they are from the cell tower to which they're connected. Cell phone transmission power can range from 1/4 watt to 2 - 3 watts depending on where they are and who you ask. When the in-air events happened, I assume both phones would have been transmitting at pretty much max power since at 9,000 ft over the desert we would have been quite a ways away from the towers.

Another thing to consider is that the COM radios also create RF interference the GPS system must deal with when they’re transmitting (16 watts each). I think the combination of all these variables contributes to why it’s “sorcery why sometimes it happens when most of the time it’s no issue”.

In any case, without additional data for now that’s my story and I’m sticking with it :)!
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MarkA
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Re: I need some G1000 avionics support in the Phoenix area

Post by MarkA »

Just to update this tread.

It turned out the root cause of the GPSs dropping out on my DA40 XLS was NOT related to interference from active cell phones in the cabin. Instead they were caused by a failing GA-35 GPS antenna connected to GPS #2. The failure started out as an intermittent hardware problem that became more frequent over the past 4 or 5 months.

Apparently, GA-35 antennas have been known to fail in such a way that they start oscillating and generating enough RF interference on their own to block the GPS signal to it and any other nearby GPS antenna. I received an email from the Garmin Field Service Engineering group last week confirming they have seen this before. Since the two GA-35 antennas are physically right next to each other on DA40s, if one antenna fails in this mode it can caused both GPSs to lose connection to all the satellites at the same time. See the following related thread for more details on how the failing GA-35 was identified and diagnosed on my plane.

viewtopic.php?t=8252

Soo… it appears sorcery wasn’t involved and the real cause of the GPS issues on N123MZ were not related to cell phones being active during flight. For now, that’s my NEW story and I’m sticking with it - at least until something else stops working :oops:
2010 DA40 XLS, N123MZ, KHIO
https://youtu.be/LuQr6mGxffg
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