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Touring Motor Gliders Association (TMGA)

PLB interference with Dynon Skyview 2020 compliant


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Dave

Gents, Here's a heads up that took me a frustratingly long time to figure out. Bottom Line: If you use a SPOT PLB (and I recommend that you do use a PLB) do not mount it anywhere close to the Skyview GPS module on the glare shield.  When Terry and I flew from Atlanta to Chico, CA he was the left seat. I mounted my SPOT on the Right side of the glare shield in front of me and sometimes clipped it to my seatbelt shoulder strap.  We had no problems with the Skyview or any other systems. The SPOT works great and gives a significant measure of security.  On the return trip, I was left seat and mounted the SPOT in front of me on the glare shield. When we left from Corning, CA there was an unusual and strong wind coming from east to west over the Sierra Nevada so we diverted north past Mt. Shasta to circumvent it. The air as a bit lumpy, so I was hand flying...great scenery. After our overnight in Mt. Home, Idaho we headed towards Wyoming in nice calm air. When I put on the auto pilot we began to experience loss of GPS signal which recurred at exact 10 minute intervals that effectively  moved the course line abruptly to the right by about 30 degrees. The autopilot redirected the plane just as abruptly in the new direction. This was unsettling since we had no idea what was happening. The disruption was only for about 5 seconds each time and self-corrected. For a while we simply disconnected the autopilot a few seconds before the next "scheduled" event. Eventually, it was found to be too distracting, and I just hand flew the plane all the way back to Pennsylvania. I later saw that the LX vario was malfunctioning as well.  Having given you the spoiler alert right up front, the diagnosis seems obvious. However, I had been flying the plane with the SPOT for a few years before the 2020 upgrade, and the Skyview was rock solid. Lots and lots of frustrating troubleshooting and data analysis was fruitless, and I won't expand on it. However, after one of the "fix-it" attempts I took the plane for a 60 minute test flight around my local area, and sure enough it was fixed. Bravo. However, a few weeks later when I flew the plane down to Atlanta in November the problem started up anew. Despair set in, but the flight was otherwise beautiful. Incidentally, I overnighted at KDAN in Virginia....very nice airport. Upon coming home I was writing an email to Terry when the obvious answer suddenly penetrated my thick skull. The reason the last "fix" worked had nothing to do with any change in the system or install. I simply had forgotten to mount the SPOT for the local test flight. During the flight to Atlanta I began to exactly write on my kneeboard  the time of the GPS disruption. At home, when I was examining the SPOT log I saw that it's communication signal to the satellite exactly corresponded to the GPS disruption times. The 2020 GPS upgrade antenna was simply more sensitive than the original equipment and was being interfered with by the SPOT.  I don't know if any other brand of PBS would do the same. Best to all for a happy, safe, and healthy flying season. And now on to the Rotax rubber replacement project.

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