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  #1  
Old 03-10-2018, 09:37 AM
krw5927 krw5927 is offline
 
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Location: Wichita, KS
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Default Garmin GA-35 Antenna Hard Failure In-Flight

I know there have been reports of this previously, but yesterday returning from Kansas City and about 20 miles from home, my Garmin GNS480 with GA-35 antenna suddenly lost GPS navigation integrity. The signal status page showed zero signal on any satellite, which has never happened before.

At the same time, I noticed the G5, Dynon Skyview, and Ipad had all lost their position locks as well. The Skyview also displayed a message of degraded attitude condition or something of that nature.

Having read of this GA-35 antenna failure before, I tried turning off the GNS480, and all the other devices resumed GPS position lock. As an experiment, I turned the 480 back on, and watched everything else lose lock immediately again. It was a very repeatable failure.

Because the GNS480 feeds ADSB out, I filed an ASRS report even though I was only in Class E and G airspace for the rest of the flight. Had I been in IMC, this failure would've been quite exciting!

I know others have had some success working with Garmin to replace the faulty antenna. Mine is several years old so probably outside of any warranty period. Any advice on working with Garmin would be appreciated - I don't exactly have a "dealer" to work with. Perhaps I just bite the bullet and buy a new GA-35?
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  #2  
Old 03-10-2018, 11:52 AM
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Brantel Brantel is offline
 
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Contact Trek Lawler at Garmin. He will most likely have you work thru a distributor (Stein) no matter what he comes up with.
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  #3  
Old 03-10-2018, 01:42 PM
Canadian_JOY Canadian_JOY is offline
 
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Kurt - I'm sorry you experienced this failure. With this failure mode the GA35 antenna turns into a GPS jammer, normally taking out all the other GPS receivers in the airplane.

While Trek Lawler is a great guy who does his best to help, the corporate line from Garmin is the source of the fault is excessive torque of the mounting fasteners. Of course that also means any warranty claim will be denied.

Dare I be so bold as to suggest that antennas should be designed so that most reasonable fastener torques don't cause the antenna to fail in such a manner as to interfere with every other receiver in the aircraft? Dare I suggest this should be documented in a Service Bulletin distributed to all owners, and that Garmin should have some skin in the game when it comes to replacing antennas which clearly have a fatal design flaw?

Nah, might as well save my breath to cool my porridge since nobody in the FAA seems to think that wiping out all the GPS navigators on an aircraft is a problem! There's a law against using cell phones on airliners, but no law against manufacturing avionics antennas that become jammers - that would be too logical.

Ok, time to hop off the soap box...
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  #4  
Old 03-10-2018, 07:45 PM
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Mike S Mike S is offline
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Steve, see this thread.

http://www.vansairforce.com/communit...d.php?t=139576

Post 6 has a lot of good info that might address your questions.
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  #5  
Old 03-10-2018, 08:01 PM
scsmith scsmith is offline
 
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Quote:
Originally Posted by Mike S View Post
Steve, see this thread.

http://www.vansairforce.com/communit...d.php?t=139576

Post 6 has a lot of good info that might address your questions.
Ah, yes, I remember now. What I stated above is not true. (post deleted) The base plate is not threaded. The screws pass through from above and get nuts on the underside. So yes, I can see that over-tightening could crush or crack the plastic cap. Especially if the antenna is attached to a curved skin. I made aluminum wedges to put between the curved skin and the base of the antenna, so it clamps down flat on the wedges.

gosh, it was only 3 weeks ago and I have already forgotten.

According to Brian, it looks like they have improved them to reduce the chance of cracking.
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Last edited by scsmith : 03-10-2018 at 08:04 PM.
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  #6  
Old 03-10-2018, 10:05 PM
Tom Martin Tom Martin is offline
 
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I had the same failure. The only gps not affected was the iPad.
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  #7  
Old 03-11-2018, 08:56 AM
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Walt Walt is offline
 
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There are other options, but you may not like the price

GPS/VHF Antenna TNC/BNC Comant CI-2580-200
GPS/VHF Antenna TNC/BNC Comant CI-2728-200
GPS/XM/VHF Antenna TNC/BNC Comant CI-2580-410
GPS/XM/VHF Antenna TNC/TNC/BNC Comant CI-2728-410
GPS Antenna TNC Comant CI-428-200
GPS/XM Antenna TNC/TNC Comant CI-428-410
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  #8  
Old 03-13-2018, 03:23 PM
TrekLawler TrekLawler is offline
 
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Hello Kurt,
thanks for the email, appreciate the heads up on this and will do what I can to help. but basically after about 5 years of troubleshooting this issue which started in 2010 we ultimately found that it was in fact an over tightening of the screws on the antenna. As much as I'd hope that an antenna could be made that would not allow this to happen doing so would most likely be such a heavy unit that you would not be able to carry any passengers, even over torquing a cylinder head will cause it to crack so not sure there is anything that could prevent an issue like this.
During this timeframe when this issue was first noted and we did not know what was causing it we were replacing them at no charge, keep in mind the GA 35 is not something we build in house, but rather have a vendor build and provide them for our kits. so it was quite a bit of money out of pocket over a 5 year period. we then found the problem with overtightening them as we could never reproduce it with the returned antennas as they were no longer under any stress during our testing. in short what was happening is the ground plane was coming loose from the internal circuit board in the unit and it was turning from a receiver to a transmitter oscillating at its tuned frequency of 1.575 GHz which as you now know is the frequency of the GPS data. we went through a couple of different shell changes with the vendor and did change to a different material that is intended to be more robust and less susceptible to the cracking if the screws are overtightened, plus there is also a big notice in the packaging about the max tightening of the fasteners in the package that has to be removed before you can install the new antenna.

with that being said, I will be happy to do what I can to help if you can get with your local Garmin dealer with the serial number of the antenna and have them contact me
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  #9  
Old 03-13-2018, 05:01 PM
krw5927 krw5927 is offline
 
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Quote:
Originally Posted by TrekLawler View Post
Hello Kurt,
thanks for the email, appreciate the heads up on this and will do what I can to help. but basically after about 5 years of troubleshooting this issue which started in 2010 we ultimately found that it was in fact an over tightening of the screws on the antenna. As much as I'd hope that an antenna could be made that would not allow this to happen doing so would most likely be such a heavy unit that you would not be able to carry any passengers, even over torquing a cylinder head will cause it to crack so not sure there is anything that could prevent an issue like this.
During this timeframe when this issue was first noted and we did not know what was causing it we were replacing them at no charge, keep in mind the GA 35 is not something we build in house, but rather have a vendor build and provide them for our kits. so it was quite a bit of money out of pocket over a 5 year period. we then found the problem with overtightening them as we could never reproduce it with the returned antennas as they were no longer under any stress during our testing. in short what was happening is the ground plane was coming loose from the internal circuit board in the unit and it was turning from a receiver to a transmitter oscillating at its tuned frequency of 1.575 GHz which as you now know is the frequency of the GPS data. we went through a couple of different shell changes with the vendor and did change to a different material that is intended to be more robust and less susceptible to the cracking if the screws are overtightened, plus there is also a big notice in the packaging about the max tightening of the fasteners in the package that has to be removed before you can install the new antenna.

with that being said, I will be happy to do what I can to help if you can get with your local Garmin dealer with the serial number of the antenna and have them contact me
Trek, I (and I'm sure others) really appreciate you coming on the board to reply! I will contact the Garmin avionics dealer in my area to see if they can help run some communication.

Also, in hopes that I don't create a new problem for myself, and for future posterity for others on the board, is the recommended torque for the GA35 antenna fasteners still 12-15 in-lbs as depicted in the installation manual linked here? http://static.garmin.com/pumac/GA35G...structions.pdf

Thanks again for your time!
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  #10  
Old 03-13-2018, 10:53 PM
TrekLawler TrekLawler is offline
 
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Hello Kurt,
yes, the recommended torque for the hold down screws is not more then 15 inch pounds.
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