ADS-B Flight ID Mismatch

Last week, I received a "courtesy call" from a fellow at FAA HQ about several occurrences of a "Flight ID Mismatch" over the past 4 months, which happened to be since I installed a GPS 175 to feed gps data to my GDL-82. He started right off by stating,"No one's in trouble" and then spoke about the Flight ID Mismatch issues. At apparently random times, it happened on 6 out of my last 24 flights, all cross-countries, typically at Class C airports. The first 4 flights after the GPS 175 installation were not flagged. I pulled up all of the PAPR reports to see for myself. I couldn't pin it down to any particular ATC facility.

I use anonymous mode as often as I can. I had not filed a flight plan for any of the flights. On one report, it showed ADS-B ID: VFR and Flight Plan ID: X instead of N as the first character in my N-number. Another report showed ADS-B ID: VFR and Flight Plan ID: (blank). One page 4 of the report, it clearly states that: "The above FP ID Mismatch field can be disregarded when no flight plan was filed for the associated flight." Pointing that out to the FAA fellow on the phone didn"t make any difference to him.

I've talked to both Garmin and my avionics supplier without getting a definite resolution. I could also return to my prior setup using the internal gps on the GDL-82, which worked without error for the prior 3 years. Not looking to dump on anyone, just looking to compare notes with someone with a similar situation.

alcladrv said:

At apparently random times, it happened on 6 out of my last 24 flights, all cross-countries, typically at Class C airports.

I use anonymous mode as often as I can.

Click to expand...

You might try a series of flights where you don't use anonymous mode prior to getting a new transponder code to enter Class C airspace, and see if this issue goes away (just as a test).

It is possible the FAA software is getting confused with the ICAO address and Flight ID change associated with coming out of anonymous mode with a new transponder code. I seem to recall seeing evidence of this in other PAPR reports.

There is a tendency for this software to propagate an aircraft position for many seconds after it stops hearing from a specific aircraft. The transition of not knowing who you are (anonymous mode) to picking up an aircraft that appeared "out of the blue" with full identification, in the same location they were expecting another aircraft, might be more than they can reliably handle. They shouldn't call this a Flight ID error, but evidence suggests that they sometimes do. The fault is really that someone called you on this issue when you and your system are doing nothing wrong.

I would be surprised if switching from the internal GDL 82 GPS position source to the externally supplied GPS 175 position source actually has anything to do with this issue.

Steve