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Pro tip: Skyview two year transponder check

Dgamble

Dgamble

Well Known Member
I was a little embarrassed when I went to have my two year transponder check on my version 12 + ADSB Skyview. I couldn't get it to go into ALT mode! I knew that ALT mode was working because I had seen it in flight on the way to the avionics shop, but it was steadfastly clinging to GND mode now that I was, well, on the GND.

I also remembered that it has been staying in ALT mode even while on the GND since one of the more recent firmware upgrades, which I just assumed was deliberate on the part of Dynon in response to this:

"This SAFO advises all operators and pilots of the need to ensure that transponders are in the
altitude reporting mode whenever their aircraft is on an airport movement area at all airports."

http://www.faa.gov/other_visit/avia...afety/safo/all_safos/media/2015/SAFO15006.pdf

The most recent change to anything related to the avionics was the installation of the ADSB kit that I bought from Van's. As part of the installation, I used the Van's supplied config file. This is what caused the highly irritating alarm when it decided that my canopy wasn't properly latched due to the lack of the canopy latch safety switch. It seems that the config file also reverted back to AUTO ALT/GND mode for the transponder.

If you find yourself in this position, just go to the transponder setup page, select AUTO ALT/GND, and set it to NONE.
 
Dave,

There's actually two different independent modes in a Mode-S transponder:

Air/GND

ALT / No ALT

So you can actually have GND+ALT or GND+NO ALT. AIR mode responds to all interrogations, whereas GND is only ground radars. ALT determines if you reply with your Mode-C (altitude) code or not when you reply.

Our auto mode is GND+ALT when on the ground which is exactly what the FAA wants. An ADS-B OUT device MUST accuratley reflect your AIR or GND state. It's actually wrong to leave it in ALT when on the ground.

I know the FAA's guidance isn't very clear on this. We keep trying to get them to change it to make it clearer for Mode-S transponders with ADS-B out.
 
dynonsupport said:
Dave,

There's actually two different independent modes in a Mode-S transponder:

Air/GND

ALT / No ALT

So you can actually have GND+ALT or GND+NO ALT. AIR mode responds to all interrogations, whereas GND is only ground radars. ALT determines if you reply with your Mode-C (altitude) code or not when you reply.

Our auto mode is GND+ALT when on the ground which is exactly what the FAA wants. An ADS-B OUT device MUST accuratley reflect your AIR or GND state. It's actually wrong to leave it in ALT when on the ground.

I know the FAA's guidance isn't very clear on this. We keep trying to get them to change it to make it clearer for Mode-S transponders with ADS-B out.
Click to expand...
Okay, so I should go back to GND+ALT as my default setting, which I'm quite comfortable with. Thanks for the heads-up on that.

In that case, did I actually need to edit the transponder settings to get the ALT to work for the two year check, or was there another way? They just seemed to be having trouble with seeing the altitude in the calibration equipment and I was surprised to find that I couldn't manually turn it on for them. That said, I kind of got the feeling that they don't do many of these... maybe the difficulty they were having was unrelated to the mode.
 
I discovered the "None" option recently when having my 2 years Xponder check. The operator testing the Xponder did not want it to be in GND mode and I did not know how to do that. He called Dynon and got the answer: set it to None for the test. Obviously you have to remember to turn it back to GND+ALT after the test is done. Good response time from Dynon over the phone by the way. As I was not on my home field I appreciated not to have to come back another day.
 
Sure wish that we could figure out a way to do this ourselves. We built the airplanes, and went through Van's acceptance documentation. Surely someone can come up with some inexpensive test gear, and process. The best that I can find around here is a guy that comes to the airport and charges $350 for his services................Tom
 
todehnal said:
Sure wish that we could figure out a way to do this ourselves. We built the airplanes, and went through Van's acceptance documentation. Surely someone can come up with some inexpensive test gear, and process. The best that I can find around here is a guy that comes to the airport and charges $350 for his services................Tom
Click to expand...

The test requires a special contraption that simulates whatever equipment is used by the ATC folks to talk to the transponder. The device is positioned about 20 ft away from the plane and checks the conformity of the signals your Xponder is broadcasting. By the way as I was attending these tests, the operator told me to also stay at least 20 ft away from the airplane because of the radiation of the Xponder antenna. I wonder if we should be aware of that when working on the avionics in the hangar. He claims that in the airplane we are OK because of the Faraday cage effect. I paid only $120 for the test but I flew to his shop.
 
Dgamble said:
In that case, did I actually need to edit the transponder settings to get the ALT to work for the two year check, or was there another way? They just seemed to be having trouble with seeing the altitude in the calibration equipment and I was surprised to find that I couldn't manually turn it on for them. That said, I kind of got the feeling that they don't do many of these... maybe the difficulty they were having was unrelated to the mode.
Click to expand...

The "appropriate" way to do this test is for them to pull on the static port until the system comes out of GND mode. This tests the auto air/gnd switch, which technically needs to be tested as part of a Mode-S test. If you had a physical squat switch, they are supposed to jack up the plane to check it.

Since they need to pull altitude to test the transponder anyway, pulling static isn't really a big deal.

If they don't want to do that, then toggling the auto mode in setup is the only way.

Mode-S and ADS-B testing is still pretty new for most shops. That's another note too- technically you must have your transponder tested by a Mode-S tester too, not a Mode-C.
 
WingedFrog said:
By the way as I was attending these tests, the operator told me to also stay at least 20 ft away from the airplane because of the radiation of the Xponder antenna. I wonder if we should be aware of that when working on the avionics in the hangar. He claims that in the airplane we are OK because of the Faraday cage effect.
Click to expand...

What about fiberglass airplanes?

The transponder is not a safety hazard. The radiation it puts out is non-ionizing, which means the only issue is heating.

While the transponder pulses at 350W, as you can see in the install manual, the max power the transponder draws only 5W of electrical power. That's because the 350W pulses are so short and infrequent that the average power is very low.

On top of this, the reply is at 1090 MHz, which is way off the most efficient water heating frequency of 2,400 MHz.

Finally, power falls off by the square of distance. A cell phone is 0.6W at 1,900 MHz and is right next to your head. Let's say 2 inches. To have the same energy as a cell phone next to your head, the transponder needs to be 8 inches away. Add in the frequency difference and it's even less.

Don't be afraid of the transponder. But do get it tested ;)

--Ian Jordan
Dynon Avionics
 
Why you can't do it yourself

todehnal said:
Sure wish that we could figure out a way to do this ourselves. We built the airplanes, and went through Van's acceptance documentation. Surely someone can come up with some inexpensive test gear, and process. The best that I can find around here is a guy that comes to the airport and charges $350 for his services................Tom
Click to expand...

First, it should not cost you $350 for a VFR Transponder check (unless maybe you are paying a lot for travel time). Full IFR check, maybe but not for a VFR check. Your first check will cost more than a normal 2 year check because an encoder correspondence check must be done - but still not $350.

The equipment to do these tests is VERY expensive to purchase and to maintain. Besides the fact that you have to be an FAA certified Repair Station to perform a legally valid transponder check.

Check out my brother's website for more info: http://www.expaircraft.com/Transponder.htm

BTW, Walt charges $95 for a VFR Transponder check .... but you do have to come to his shop.
 
dynonsupport said:
The "appropriate" way to do this test is for them to pull on the static port until the system comes out of GND mode. This tests the auto air/gnd switch, which technically needs to be tested as part of a Mode-S test. If you had a physical squat switch, they are supposed to jack up the plane to check it.

Since they need to pull altitude to test the transponder anyway, pulling static isn't really a big deal.

If they don't want to do that, then toggling the auto mode in setup is the only way.

Mode-S and ADS-B testing is still pretty new for most shops. That's another note too- technically you must have your transponder tested by a Mode-S tester too, not a Mode-C.
Click to expand...

No disrespect but can you point me to the CFR reference you are referring to for the "required" altitude testing and mode S air/grd testing requirements when accomplishing a transponder check per 43 (E)?

There are much easier ways to put an aircraft in air mode than jacking (do you really think we jacked airliners everytime we did a xpdr check)?
 
Last edited:
Yes, the new txponder testers are very expensive. Our shop spent $20,000 for a new ADS-B tester. Plus, it has to be certified every year.
 
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