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Uh oh...Navworx AD


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I think this goes back to "what does 'equivalent performance' mean?"  It almost sounds like Navworx just decided their box meets all the performance requirements and so decided to set their SIL bit accordingly, and the FAA is saying that if that is not authorized by them it's not allowed.


I have to say, I said in other threads that there are problems with the "equivalent performance" language since it's not defined, and that some manufacturers and owners might get a rude awakening regarding their equipment.  I'm not saying I told you so...but I did.   :laughter-3293:

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  • 5 months later...

Hmm, still waiting for a resolve on this. The FAA has its arms folded and NavWorx is still selling away claiming certification. The next system up is Skyguard which is more expensive (and looks to be the same implementation), then the Freeflight which is double the price and is also similar in design. I hope they resolve this before 2020.

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Tom, I'm trying to keep up on the compliance issue with our ADS-B units.  I have the SkyGuard transceiver which is 978 UAT "out" and 978 and 1090 "in".  Recently, I sent my unit in for upgrade of the internal GPS and upgrade of the firmware which was required to meet the most recent FAA requirements.  Don Houtz, who owns and runs SkyGuard company, wrote me a short explanation of what he did to upgrade my unit.  Don indicates that this is now (again) 2020 compliant.  Along with the GPS upgrade, a new GPS antenna was also sent to me.  This is a "pre-amplified" antenna.  If I understand correctly, the FAA has worked with the non-certified WAAS GPS ADS-B manufacturers and has come up with the solution of having the units send SDA=2 and SIL=3 codes which ATC has been instructed to recognize as correct for a non-certified WAAS unit.  This results in the non-cert ADS-B units once again qualifying to be sent TIS-B info and performing in compliance with 2020 rules for "non-certified" ADS-B.  My unit is working extremely well.  Here's Don's explanation of work done on my unit.  I would be interested in your comments:



Hi Dick:   We performed the GPS/Firmware upgrade to your Transceiver
                 We did a full bench test and everything passed OK.
                 You will receive a new GPS antenna with your returned unit.
                 Be sure to read the instruction sheet on how to attach it.
                 You will no longer use the original GPS antenna.
                 Also, SDA is now set to 2 and SIL is set to 3 which is appropriate
                 For this new GPS/Firmware.   With these new values, your Transceiver
                 Will now begin to receive TIS-B traffic broadcasts from the ADS-B
                 Ground Station Towers.
                 We will ship back your unit tomorrow and will send a USPS
                 Tracking number when we have it.
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For anyone experiencing the frustration of trying to "pass" the ADS-B validation for the $500 rebate and are failing repeatedly the "air-ground" portion, don't feel alone.  This is a very common problem across the entire community and is a continuing source of frustration for installers and the manufacturers both.  The FAA points to installers and manufacturers but it seems more likely an algorithm issue with the FAA's system in interpreting the GPS signal.  And in the meantime, after two unsuccessful attempts at the validation flight I finally got a green "pass" on all aspects today.  I'll be happy to discuss how I was able to do this via a PM with anyone having this issue.

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Olav, I will PM you but for a general discussion so all other ADS-B owners can learn by my experience I will post this reply.  I have the SkyGuard TWX and failed to pass the FAA test.  I sent Don @ Skyguard a note and Don replied to me that the "non-certified" ADS-B units will not get a "green" report but this is expected and is OK.  The following is a series of questions and answers between myself and Don.  If you might find the time to read the following i would appreciate it.  I then would like to either talk to you by phone or by PM in order that i might better understand this. If you start at the bottom of my correspondence with Don, you will see my original note to Don.  This states that my ADS-B unit passed the SIL and CDA but failed the "NIC" portion of the test..  As you go "up" you will see Don's explanation why I'm "OK" and the more recent communications appear.


From: Don Houtz <Don@SkyGuardTWX.com>
To: 'Dick Harrison' <reh3335@yahoo.com>
Sent: Wednesday, August 31, 2016 3:54 PM
Subject: RE: From Dick Harrison - 2nd attempt to successfully pass FAA ADS-B Performance Test

Dick:  The GPS in your unit is performing fine and exactly as it is designed to do.
            The RED in the report is just an indicator that some of the GPS accuracy readings
            Were outside of what the FAA expects for a TSO’d GPS source.  Since you have
            An experimental version, it does not need to be TSO’d and is not required to meet
            The requirements of a TSO’d GPS.
            Also, you do not need to demonstrate anything to the FAA.   Your unit is compliant
            To the 2020 mandate for experimental/LSA aircraft because we have tested it to such
            Requirements and are stating in the install guide that it meets these requirements.
            The only reason to request the ADSB compliance report is to tell you if everything is working
            As you would expect.   In looking at the report, I am telling you that it is.
From: Dick Harrison [mailto:reh3335@yahoo.com]
Sent: Wednesday, August 31, 2016 1:25 PM
To: Don Houtz <Don@SkyGuardTWX.com>
Subject: Re: From Dick Harrison - 2nd attempt to successfully pass FAA ADS-B Performance Test
Don, I know your very busy so thanks for the quick reply.  Do I understand you to say my GPS will report better the more I use it?  Or is it performing OK as it is now.  Would I need to be completely "red free" on this report for the FAA to consider my ADS-B system to be 2020 compliant.  Will I eventually need to demonstrate to the FAA how my ADS-B system performs or worry about taking this test again or any other FAA performance tests in order for the FAA to list me as being 2020 compliant?
From: Don Houtz <Don@SkyGuardTWX.com>
To: 'Dick Harrison' <reh3335@yahoo.com>
Cc: 'Shane (Adventure Pilot)' <shane@adventurepilot.com>
Sent: Wednesday, August 31, 2016 9:40 AM
Subject: RE: From Dick Harrison - 2nd attempt to successfully pass FAA ADS-B Performance Test
Dick:   It is not that the NIC parameter failed, the report is indicating that there
            were a few readings where the value was below the minimum range expected
            by the FAA report.
            It is a fairly complicated explanation, but NIC represents the GPS horizontal
            containment boundry.   This is reported directly from the GPS which is calculating
            this boundry value based on the number of satellites it is receiving and the accuracy
            of the satellite transmissions.
            If you look at the detail, there were 55 readings out of 1508 that had a value of
            6.   The FAA report is expecting all readings to be between 7 and 11.   As you fly,
            the GPS gets more accurate as it acquires additional satellites and goes through it’s
            accuracy calculations.   This is fairly normal behavior for WAAS GPS’s, so I would not
            worry about it.
            All else is fine with the report.
From: Dick Harrison [mailto:reh3335@yahoo.com]
Sent: Tuesday, August 30, 2016 8:56 PM
To: Don Houtz <don@skyguardtwx.com>
Cc: Shane (Adventure Pilot) <shane@adventurepilot.com>
Subject: From Dick Harrison - 2nd attempt to successfully pass FAA ADS-B Performance Test
Hi Don.  I took my airplane up today to test the SkyGuard after you reprogrammed it and returned it to me.  The 1st performance report which I sent to you a few weeks ago indicated that I did not pass "SIL" and "CDA".  I sent you my unit and you reprogrammed it.  The performance test I did today, with the reprogrammed unit, shows that I'm now OK for "SIL" and "CDA" but that I failed to pass the "NIC" test.  I'm wondering if the parameters of my flight today may have affected the performance?  At one time during my flight, I flew down and did a low pass over my friend's airfield and was well below 1,000' AGL for a brief period of time.  The FAA ADS-B performance summary sheet is attached.
Dick Harrison
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Fire off a PM to me with a good phone number and I will give you a call and we can discuss.   I think you are an hour ahead of my (Mountain Daylight Time) location so I will try to call before 2100 your time...or tomorrow if that is better for you.





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  • 1 month later...

AD 2017-11-11.pdf is now coming into effect.

Essentially, when navworx changed the SIL from 0 to 3, it violated the STC it was created under. Here's a comment and the FAA's justification:


Request: AOPA requested the FAA further explain its finding that the affected units create an unsafe condition. Many commenters questioned the FAA's determination that the units present an unsafe condition, and asked whether any units have actually caused a collision or safety incident. Many other commenters stated they have been operating with the NavWorx unit and find it accurate and reliable. Several commenters stated the NavWorx units increase safety and noted that the National Transportation Safety Board has recommended ADS-B units to the flying public.

FAA Response: The FAA's safety concern is primarily that of integrity, and not necessarily accuracy, with respect to the NavWorx ADS-B unit's performance requirements. Accuracy refers to the probability of the unit's true position in relation to its reported position.2 Integrity refers to the trust that can be placed in the correctness of the information provided by the unit and is specified by a SIL value. The SIL value is set based on design data from the GPS position source manufacturer and reflects the probability that the position source will provide incorrect data without providing an alert. This depends on whether the GPS has fault detection and exclusion, where the equipment will detect a faulty satellite and exclude it from the navigational calculations. If the GPS does not have fault detection and exclusion, the probability that the position source will provide incorrect data increases. Commercial position sources, such as the SiRF IV GPS used in the NavWorx P/N 200-0012, 200-0013, and 200-8013 units, do not have fault detection and exclusion capabilities. This is significant in the event a GPS satellite signal fails or a GPS “signal-in-space error” occurs.

This is a pretty good justification actually for this AD.

Now that said:


Request: Many commenters, including AOPA, requested that, since the internal GPS is the issue with the NavWorx unit, the AD allow the ADS-B units to use an external GPS position source or, similarly, that the AD not apply to units using an external GPS position source. FAA Response: We agree. The only external GPS position source approved by the FAA for interface with the ADS600-B is the Accord NexNav mini LRU GPS Receiver P/N 21000 (Accord external GPS).6 We revised the AD to allow interfacing the ADS-B unit with an Accord external GPS as an optional corrective action. For operators who wish to interface with other external position sources, under the provisions of paragraph (f) of this AD, we will consider requests for approval of an Alternative Method of Compliance (AMOC) if sufficient data is submitted to substantiate that the unit would provide an acceptable level of safety.

In addition, other alternate means of compliance are allowed, such as changing the software back to SIL 0. There's a lot of very good reading in this AD.

Finally: this AD is a golden example of how I continuously tell people that ADs can apply to light sport aircraft. To reiterate:



Request: EAA and two individual commenters requested the AD not apply to experimental or light sport aircraft, since they are not regulated in the same manner as type-certificated aircraft. EAA states the FAA should address any valid airworthiness concerns with parts intended for experimental aircraft through a Special Airworthiness Information Bulletin (SAIB) or safety alert for operators (SAFO). Two commenters requested the AD apply to experimental aircraft, because those aircraft operate in the same airspace as type-certificated aircraft and should use equipment with the same integrity. A few commenters, including AOPA, requested we clarify whether the AD applies to experimental aircraft.

FAA Response: We agree to clarify this issue. We confirm that the AD applies to all aircraft, including experimental, and we revised the AD to clarify the applicability. We made this AD applicable to the ADS600-EXP P/N 200-8013 units because the design of the Model ADS600-EXP P/N 200-8013 is substantially identical to the Model ADS600-B P/N 200-0012 and 200-0013, specifically with regard to the internal GPS and the SIL setting. While some commenters are correct that the FAA has chosen to minimize regulations on experimental aircraft because of the level of the safety risk, these risks normally apply to the individual airplane and do not affect the overall NAS. The safety risks defined in this AD extend beyond one aircraft and could affect many other aircraft as well as ATC. Therefore, we find it necessary to include experimental aircraft in the AD's applicability. We do not agree that an SAIB or SAFO would be an appropriate solution. These documents contain information and recommended actions that are voluntary and not regulatory. Moreover, an SAIB is issued only for airworthiness concerns that do not rise to the level of an unsafe condition. The mission of the FAA is aviation safety. ADs are used by the FAA to correct known safety defects. It would be contrary to the intent of the FAA's mission and statutory authority to exclude certain aircraft when we have determined that a part installed on those aircraft has a safety problem.

Here's the applicability section:


(a) Applicability This AD applies to the following NavWorx, Inc., Automatic Dependent Surveillance-Broadcast (ADS-B) Universal Access Transceiver units (unit) installed on aircraft certificated in any category, including experimental: (1) Model ADS600-B part number (P/N) 200-0012; (2) Model ADS600-B P/N 200-0013; and (3) Model ADS600-EXP P/N 200-8013.


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