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G3X Touch All GarminTransponder Certification

jliltd

jliltd

Well Known Member
We have a G3X Touch system in an RV-8. It uses a GTX 45R and a Gap 26 AOA/Pitot tube.

My best friend took the aircraft to a local repair station to have a Transponder Certification done. They had no idea how to put the remote 45R transponder in Ground Test mode. They had no experience with nor did they realize the airplane had an AOA probe pitot tube. Their test set didn't have proper adapter pads to connect the static test line to the flat side of the fuselage *rivet" style static ports.

The technician attached their test set pitot tube line to the GAP 26 AOA/pitot tube by slipping a vinyl tube over the entire length of the tube. Since they didn't have provisions to connect to the fuselage static ports they just left them off. Once the aircraft systems were fired up they could not get a transponder beacon code of any kind since they didn't realize or know that the 45R had to be placed into Ground Test mode before it would transmit any beacon like it does in the air. They also couldn't get any airspeed readings on the GDU 465 EFIS.

So that's when the owner called me for advice. I told my friend that the repair station should review the manuals for the G3X Touch and GTX 45R before doing any more testing. I looked up the G3X Touch manual and it said that the AOA and static ports on the aircraft needed to be both attached to the static line of the test set while the pitot tube be attached to the pitot line of the test set. There are grave warnings about damaging sensors if pitot and static ports are not all connected properly to the test set.

I advised my buddy to abandon the cert test until we could find out more information.

So some questions for those in the know:

1. Where are the AOA ports on the GAP 26? Would slipping a test set pitot line down the entire length of the pitot tube cover the AOA ports?

2. What kind of adapter would pick up the AOA pressure ports so they could be interconnected with the fuselage static ports and the test set?

3. Why was the GDU not showing any response to test set pressure applied to the pitot with the system powered up on the ground? Meanwhile I know how to set the remote transponder into Ground Test mode (unlike the repair station guy).

4. Should we take the airplane around the patch to see if the pitot/static/AOA sensors in the GSU 25 have been compromised?

Thanks in advance,

Jim
 
jliltd said:
We have a G3X Touch system in an RV-8. It uses a GTX 45R and a Gap 26 AOA/Pitot tube.

My best friend took the aircraft to a local repair station to have a Transponder Certification done. They had no idea how to put the remote 45R transponder in Ground Test mode. They had no experience with nor did they realize the airplane had an AOA probe pitot tube. Their test set didn't have proper adapter pads to connect the static test line to the flat side of the fuselage *rivet" style static ports.

The technician attached their test set pitot tube line to the GAP 26 AOA/pitot tube by slipping a vinyl tube over the entire length of the tube. Since they didn't have provisions to connect to the fuselage static ports they just left them off. Once the aircraft systems were fired up they could not get a transponder beacon code of any kind since they didn't realize or know that the 45R had to be placed into Ground Test mode before it would transmit any beacon like it does in the air. They also couldn't get any airspeed readings on the GDU 465 EFIS.

So that's when the owner called me for advice. I told my friend that the repair station should review the manuals for the G3X Touch and GTX 45R before doing any more testing. I looked up the G3X Touch manual and it said that the AOA and static ports on the aircraft needed to be both attached to the static line of the test set while the pitot tube be attached to the pitot line of the test set. There are grave warnings about damaging sensors if pitot and static ports are not all connected properly to the test set.

I advised my buddy to abandon the cert test until we could find out more information.

So some questions for those in the know:

1. Where are the AOA ports on the GAP 26? Would slipping a test set pitot line down the entire length of the pitot tube cover the AOA ports?

2. What kind of adapter would pick up the AOA pressure ports so they could be interconnected with the fuselage static ports and the test set?

3. Why was the GDU not showing any response to test set pressure applied to the pitot with the system powered up on the ground? Meanwhile I know how to set the remote transponder into Ground Test mode (unlike the repair station guy).

4. Should we take the airplane around the patch to see if the pitot/static/AOA sensors in the GSU 25 have been compromised?

Thanks in advance,

Jim
Click to expand...
Hello Jim,

You are correct that is is very important to connect pitot, AOA, and static ports together before pumping down the system to take the aircraft to a high altitude. Not doing so exposes the differential pressure sensors in the GSU 25 to differential pressures in excess of the design pressure and will damage them.

There are two drawings/images in the GAP 26 section of the G3X Touch installation manual that show the location of the pitot inlet (center of probe) and AOA inlet (just below the pitot inlet).

I am sure guys like Walt who do these tests all the time can provide more details on the apparatus typically used to connect to the pitot/AOA probe, but since the pitot and AOA ports are on the end of the probe, it is not difficult to slip an adapter over the probe to block the drain ports on the bottom, while leaving the end open for the test set to be able to draw down the pitot/AOA both at once (with the static port).

We probably don't know enough about what was happening to speculate on why there was no indication on the PFD, but of course that would be abnormal.

Thanks,
Steve
 
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I'll try to keep this short...
First off a "transponder cert" 91.413 does not require testing the P-S system or altimeters, that test belongs to the IFR 91.411 cert.

When I do an IFR cert I connect directly to the AHRS, if there is a analog alt it comes out and is tested on the bench.

The reason for the direct connect is:
1) I can assure that all ports are connected to avoid damage, if a large leak develops when the system is at altitude damage to components may result.
2)Ir removes the rest of the P-S system from the test which will have some leakage. The test requires 'each altimeter' be tested for leakage at 18K ft, can't do that when the rest of the system is hooked up.
3) There is no requirement/need to test the P-S system at 20K ft., the static system is tested at 1K ft above ground on non-pres aircraft.
4) There is no requirement to test the pitot system at all on non pressurized aircraft, the pitot test is 'optional'.

The static system is then tested at 1K above ground level to assure it meets the leak rate of <100 ft/min.

I have had people come to me after they tried with another shop that wasn't familiar with the G3X system. Two of my customers had their AOA sensors blown by the shop attempting to do the test.

Chances are when the company you were using was trying to pressurize the P system they failed to plug the vent holes on the GAP26

PS: I do wish Garmin would work with a company like Cobra Systems to come up with a 'proper' pitot probe adapter for the GAP26
 
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Where are you located? The Hayward, CA area?
I had my ifr pitot-static/transponder test done yesterday, by Precision Static Testing at KLVK. (He can travel locally to you, too). He has all the equipment for Van?s style static ports, pitot tubes with AOA, etc., and he knows how to use it.
 
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