Leak proofing a roof mounted GPS antenna
 

We have a Garmin G3X system that came with a low-profile teardrop shaped GPS antenna that we mounted to the roof just behind the front seats. It's mounted with four flat-head screws that penetrate the canopy and attach with nylock nuts on the inside. There doesn't appear to be any sort of gaskets or weatherproofing seals that go with it, so our first concern is rain leakage. It seems that rain water will pool at the screws and eventually leak into the cockpit.

Does anyone else have one of these similarly mounted? How do we leakproof it without compromising the antenna?

I've been flying for over three years with two of them mounting on top of the empennage just behind the baggage bulkhead. No leaks on either of them. I didn't do anything to seal the joint.

It's not uncommon toe a little silicone sealant under the antenna, but it's good to make sure the screws have a good solid seat on the metal part of the antenna as well as the ground plane inside the plane. As Bob said, they do not usually pose a leak problem. A lot of antennas have a gasket under them, which does a good job of sealing them.

Bob,

Thanks for your reply. I have one dumb question - have you ever allowed your plane to get rained on?

I'm not flying yet, but I put a small fillet seal around the perimeter using proseal, and I put a little bit of silicone under the head of the screws. It's also common to fill the counterbores with caulking, flush with the surface.

Per the EAA video on antenna installs, I took their recommendation and used some siliconized latex caulk from Lowes.

Dries clear, water cleanup, and works great!

Don't exceed 15 in-lbs on those mounting screws! Garmin claims this can crack the cap on the antenna causing failures!

I used the same process the airlines use in their line maintenance and created a fillet of proseal around the perimeter of the antenna to seal it. The Screw heads were then covered and seal with proseal as well. If it needs to be removed, the proseal is removed from the screw tops and the fillet broken.