SAFO 17002: Proper ADS-B and Transponder Testing Procedures
Key Takeaways
- SAFO 17002 warns that improper ADS-B OUT and transponder ground testing can transmit false signals to nearby aircraft and ATC – in one documented case, a ground test created a false TCAS II Resolution Advisory on a Boeing 737 on approach, disrupting area operations for 30 minutes.
- The FAA recommends that any time simulated altitude is induced, the transponder be placed in standby or turned off unless effective antenna coupling and shielding are in use.
- The VIAVI UC-584 Universal Coupler (and UC-584Dual for dual-antenna installations) fits most L-Band antennas and provides greater than 20 dB of signal isolation – reducing or eliminating the need to coordinate with ATC before conducting ground tests.
- PJi carries the VIAVI AVX-10K avionics test set – the current replacement for the discontinued IFR6000 and IFR6015 – along with UC-584 and UC-584Dual antenna couplers compatible with all three units, supporting SAFO 17002-compliant transponder and ADS-B OUT testing.
When performing ground tests on aircraft transponder and ADS-B OUT systems, using the right equipment and procedures isn't just a best practice – it's a safety imperative. Improper testing can transmit signals that interfere with air traffic control operations and TCAS-equipped aircraft in the vicinity, with real and documented consequences.
In this article, we'll explain what FAA Safety Alert for Operators (SAFO) 17002 requires, why it matters, and how antenna coupling equipment provides a compliant, practical solution for maintenance personnel performing these tests.
What Is SAFO 17002?
Safety Alerts for Operators (SAFOs) are FAA publications that communicate important safety information and recommendations to the aviation community. SAFO 17002, issued February 6, 2017, addresses the hazards associated with improper ground testing of ATC transponders and ADS-B OUT systems.
Background
The FAA received reports of transponder and ADS-B OUT ground test events in which information – including simulated altitude – was transmitted from the test aircraft and received by aircraft in flight. In at least one documented instance, an ADS-B OUT system ground test created a false airborne target that generated a Traffic Alert and Collision Avoidance System II (TCAS II) Resolution Advisory (RA) on a Boeing 737 on approach. The pilot's reaction to the RA required unnecessary maneuvering in congested airspace and initiated ATC re-sequencing actions that affected multiple aircraft and disrupted operations in the area for approximately 30 minutes.
Discussion
Transponders and ADS-B OUT systems operating under test conditions transmit aircraft-specific information, including position and altitude data. These tests frequently involve altimetry checks in which air pressure is induced into the pitot-static system to simulate operation at various altitudes. When transmission lines are not directly connected to test equipment, antenna coupling should be used to prevent test signals from propagating in a way that could interfere with ATC operations or with TCAS- and ADS-B In-equipped aircraft in the area.
FAA Recommended Actions
The FAA recommends that repair stations and maintenance personnel performing transponder and ADS-B OUT system testing evaluate their current procedures and test equipment to ensure uninhibited transmissions are prevented. Specifically:
- Any time simulated altitude is induced, place the transponder in "standby" or turn it off if effective antenna coupling and shielding are not available during altimetry testing.
- Review the latest revisions of AC 43-6, Altitude Reporting Equipment and Transponder System Maintenance and Inspection Practices, and AC 20-165, Airworthiness Approval of Automatic Dependent Surveillance – Broadcast OUT Systems.
Questions or comments regarding this SAFO should be directed to the FAA Aircraft Maintenance Division at (202) 267-1675.
How Can Antenna Coupling Equipment Help Solve This Problem?
The VIAVI AVX-10K Flight Line Test Set includes an antenna shield as a standard accessory, designed to block transmissions from the upper or lower antenna during over-the-air testing. While this helps, it doesn't fully address the problem for all configurations.
A more complete solution involves placing a coupler over the transponder antenna and using the antenna shield for dual-antenna installations. The VIAVI UC-584 Universal Coupler fits most L-Band antennas and is compatible with the AVX-10K, as well as the discontinued IFR6000 and IFR6015 units still in use in the field. For dual-antenna setups, the UC-584Dual provides equivalent coverage across all three platforms.
Key benefits of the UC-584 and UC-584Dual couplers include greater than 20 dB of signal isolation, prevention of uninhibited transmissions during testing, and the ability to reduce or eliminate the need to coordinate with ATC before conducting ground tests.
The Bottom Line
SAFO 17002 is a clear reminder that transponder and ADS-B OUT ground testing carries real risk when proper shielding is not in place. Antenna coupling equipment provides a practical, FAA-aligned solution that protects nearby aircraft and ATC operations while allowing maintenance teams to conduct thorough, compliant system checks.
Pilot John International® (PJi®) offers the VIAVI AVX-10K avionics test set – the current-generation replacement for the discontinued IFR6000 and IFR6015 – along with UC-584 and UC-584Dual antenna couplers compatible with all three units. Contact our aviation specialists by phone, email, or live chat for expert guidance on selecting the right test equipment and accessories for your operation.
