SV-261 Static System Test Mode

[kellym]

Just read https://www.aopa.org/news-and-media...ce-monitor?utm_source=epilot&utm_medium=email
with regard to ADS-B output during a test being picked up by ground station and airliner causing airliner to take evasive action.
When the Skyview system is put in test mode for static system testing, does it do anything to prevent output or mark the signal that it is test, not real traffic at say 20,000 ft? Or does the technician doing the testing need to shield the antenna to prevent signal from being picked up by others?

 

[Rhino]

The article references a UUT test, which is a full system operational test that transmits data. They must use precautions to prevent that signal from going outside the test environment (dummy loads, faraday cages, etc.). The HDX test mode for pitot/static and transponder diagnostics are limited tests of the internal systems. They don't broadcast the kind of data that a UUT test does (unless something went very horribly wrong), so the standard UUT test precautions are not required.

 

[kellym]

The article references a UUT test, which is a full system operational test that transmits data. They must use precautions to prevent that signal from going outside the test environment (dummy loads, faraday cages, etc.). The HDX test mode for pitot/static and transponder diagnostics are limited tests of the internal systems. They don't broadcast the kind of data that a UUT test does (unless something went very horribly wrong), so the standard UUT precautions are not required.

In reading the install manual, it covers the situation, by instruction you to manually switch or otherwise verify the transponder is configured in GRND mode as well as switching the pitot/static system to test mode. That will ensure that any plane or ground station receiving the signal will see the aircraft is on the ground regardless of the reported altitude. Hopefully that is sufficient to avoid any TCAS issues for planes that have TCAS.

 

[Rhino]

It doesn't actually say that prevents the system from transmitting, but yes, as I said, the test modes (and I assumed the instructions would be followed correctly) only test the internal systems. He lso,only asked about the static system. I just tossed in the transponder to be thorough. Regardless of how you want to phrase it, he doesn't need any shielding or similar precautions to prevent spurious signals getting out like is required on a UUT test, and that was his concern.

 

[kellym]

The article references a UUT test, which is a full system operational test that transmits data. They must use precautions to prevent that signal from going outside the test environment (dummy loads, faraday cages, etc.). The HDX test mode for pitot/static and transponder diagnostics are limited tests of the internal systems. They don't broadcast the kind of data that a UUT test does (unless something went very horribly wrong), so the standard UUT test precautions are not required.

With any of the Skyview current software, as far as I am aware, the system on boot automatically does the internal testing of the transponder. That is not the question. You have to do a full system test every two years, which will involve both the transponder and static system where the transponder is in fact on and transmitting. The antenna needs to be shielded, or at a minimum the transponder has to be manually switched to ground mode only, so that when the static pressure equals say 20,000 ft, it is not going to be shown as traffic, whether the aircraft in flight gets the signal directly or relayed by a ground station. The static system test mode just protects the Skyview from getting scrambled by vertical changes with no horizontal motion. Who ever has the capability of certifying a transponder needs to know both items before proceeding with the full operational test.

 

[Rhino]

Actually the question was do you need shielding for user static testing. The full two year certifying test you mention is the UUT test, which wasn't what was asked about. Two very different tests. You simply wanted to know if the local system test required the same kind of RF precautions the UUT test does, and the answer is no. The built-in static test the OP mentioned does not require shielding, nor does the transponder test. I worked avionics for 20 years.

 

[thibault]

Rhino, What is “user static testing”, “local system test” or “built-in static test”?

The OP definitely mentioned static system testing. I think he meant the required 2 year test for IFR, the UUT. That is 91.411 and definitely requires that the transponder output the same data as the source, to within 125 feet, on a “sufficient number of test points”.

To do that on an installed system in an A/C, the static pressure sensed by the ADAHRS has to be manipulated and the transponder antenna has to radiate the data. Dynon says ensure the transponder is in ground mode for testing and the EFIS is in test mode. Pretty sure that is why the testing “is safe”.

 

[Rhino]

He said the UUT was what he saw in the article, and mentioned static system testing, which I took to mean the pitot static system self test capability built into the Skyview. He wanted to know if those required the same sort of RF shielding the UUT tests require. I was also guessing he intended to include the built in transponder test, but that doesn't really matter, since neither of those tests actually transmit data, and thus don't require RF shielding. If I misunderstood, and he actually meant something else, I'd be glad to phrase my answers differently.

 

[kellym]

He said the UUT was what he saw in the article, and mentioned static system testing, which I took to mean the pitot static system self test capability built into the Skyview. He wanted to know if those required the same sort of RF shielding the UUT tests require. I was also guessing he intended to include the built in transponder test, but that doesn't really matter, since neither of those tests actually transmit data, and thus don't require RF shielding. If I misunderstood, and he actually meant something else, I'd be glad to phrase my answers differently.

I took the article to mean the static AND transponder testing required for both VFR and IFR for an aircraft to operate in areas requiring mode C and/or ADS-B. There is no way to comply with those requirements without both a separate static system test set and a transponder test set.
The only difference is how many data points are required for IFR vs VFR compliance. In both cases there is a two year requirement, which makes it idiotic to do them separately. Yes, one can leak check the static system independently if it is opened in between the two year test, and no need for the transponder to do that. That is not a "self-test". The only built-in test besides booting correctly that I am aware of is IF you have dual ADAHRS.
Yes, it checks to see if altitude derived from the static system barometric setting is appropriate for the GPS altitude, but I wouldn't begin to call that a self-test, as it is only a crude measure of system accuracy and altimeter setting input.
Point being, other than using a manometer to do a pitot pressure test for airspeed accuracy, and some means of pulling a vacuum to check for static system leaks, there isn't any testing for the builder/user to do. The referenced article was about an avionics tech doing a real live transponder test that caused a TCAS problem for an airliner. That is not something that a builder is going to do unless they have access to and proper training to use a transponder test unit.
Kelly
A&P/IA

 

[Rhino]

Correct. He won't be doing a UUT. That's why he doesn't need the kind of RF shielding they use during those UUT tests.