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ADS-B Out Findings: FID, Filed Callsign, and Flying Non-Functional ADS-B Out Systems

Jun 24, 2020
Paul Damschen UA Senior Test Pilot / DER

As operators settle into the world of Automatic Dependent Surveillance-Broadcast (ADS-B) Out, the Federal Aviation Administration (FAA) is taking a close look at how associated changes are affecting the industry and air traffic. A recent FAA ‘Equip 2020’ industry meeting presented two areas of significant interest:

  1. The mismatch of Flight ID (FID) and filed Callsign
  2. How to deal with the need to fly an airplane with non-functional ADS-B Out systems in light of the new airspace requirements

Flight ID (FID) and Filed Callsign

The FID issue has been with operators as a teething pain for several months now. Some avionics systems have a fairly complex method of modifying or changing the FID. However, it is imperative that flight crews understand how this is accomplished and verify the FID prior to dispatch. To be clear on FID requirements;

  • Part 91 Operators: FID is your tail number (N1234A for example)
  • Part 135/121 Operators: FID is your dispatch Callsign for that flight (AA1234 etc.)

Failure to check the FID and get it wrong will grab the attention of Air Traffic Control (ATC). In the event the FID has been entered incorrectly for any reason, be sure to correct it immediately just as if it were an incorrect squawk code. Also, avoid confusing your four-digit squawk code with the FID; they’re not the same and are two distinctly different pieces of data on the ATC side. Please be aware: as of this writing, a significant number of FID errors are caused by ATC coding. Therefore, be sure to know your filed Callsign and don’t just assume it’s your error.

Flying with Non-functional ADS-B Out Systems

The vast majority of ADS-B Out systems in the market are driven by a Satellite-Based Augmentation System (SBAS) GPS such as the UA SBAS-Flight Management Systems (FMS). These systems have the ability to function as primary navigation systems with internal capabilities for determination of both accuracy and integrity of the airplane’s GPS position. 

Some systems, however, are lacking the ability for SBAS correction (usually those referred to as TSO C129 GPS instead of TSO C146 WAAS/SBAS ), requiring an adequate Receiver Autonomous Integrity Monitoring (RAIM) prediction for the route of flight. This must be accomplished online using the FAA Service Availability Prediction Tool (SAPT), which can be found here

Note: SBAS GPS systems DO NOT have to use this tool. If your FMS GPS system qualifies for Technical Standard Order (TSO) C146 or C145, you can avoid using SAPT. 

If you are required to use this tool, be sure to know three key pieces of data:

  1. GPS engine TSO certification level (TSO C129 or C196)
  2. System mask angle (either 2 or 5 degrees)
  3. If the system uses baro-aiding

The information above should be available in the aircraft operator’s manuals, Approved Flight Manual Supplements (AFMS), or Aircraft Flight Manual (AFM).  All three pieces of information need to be entered correctly into SAPT to generate an accurate calculation for dispatch.

What happens if SAPT says there’s no adequate coverage for the route of flight? On the same page as SAPT, there’s another tool called ADAPT, or ADS-B Deviation Authorization Pre-Flight Tool. With ADAPT, you can fill out the necessary information and hopefully obtain authorization to conduct the flight. Note: Allowances for non-ADS-B Out functional flights is entirely at the discretion of ATC.

Here’s a tip: if you have an unsatisfactory result, try calculating RAIM +/- a half hour or so and view the results – it may eliminate the issue. There is a RAIM summary page available as well for a comprehensive view of the coverage (again, you’ll need to know if your system uses baro-aiding).

What Are the FAA’s Next Steps?

As the dust settles and flight crews complete their transition to an ADS-B Out operating environment, the FAA has several steps they wish to take:

  1. Reduce the number of ground based navaids by about 50%.
  2. Reduce radar sites, referred to as “radar divestiture.”
  3. Develop ADS-B In functions using ADS-B In traffic data for use as a traffic management tool.  For example, “AA1234 cleared for the visual following AA5678 at your twelve o’clock position, five miles.” With ADS-B In, you’ll be able to accomplish this task with the electronic ADS-B In data in the cockpit.

For international operators, ADS-B is coming to remote airspaces near you. ADS-B Out transmissions can be “heard” by satellites overhead and can be transmitted to ATC. For many remote areas with inadequate surveillance, FAA and other ATC’s around the world are moving forward with plans to require ADS-B Out in those spaces to support the surveillance requirements there. Failing to have ADS-B Out in those airspaces will require a major reroute to your flight plan. We’ll talk about this more in the future as it progresses.

Stimulus Programs Available

Many aircraft that do not have ADS-B Out equipage have been grounded until modifications can take place. With the slowdown due to the COVID-19 pandemic, we’re seeing an opportunity for those aircraft to get into the shop and become compliant. UA is currently working in concert with its Authorized Dealer / Integrator network to offer highly competitive incentives for upgrading now through August 31, 2020. Uniquely crafted for your aircraft, UA’s Stimulus Programs are designed to work with your budget. Learn more here or contact your UA Sales Representative.


Paul Damschen is a Universal Avionics Senior Test Pilot and an FAA Designated Engineering Representative. He has several thousand hours of developmental flight test experience on over 80 make and model aircraft on many systems and aircraft modifications.

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