Incidents of improper ground testing of transponder and ADS-B OUT equipment have resulted in false position information, including simulated altitude, being transmitted from the test aircraft and received by aircraft in flight. As a result of these reports, the FAA has issued a Safety Alert For Operators to advise them of the problem and recommend solutions.
According to the FAA, in at least one instance, an ADS-B OUT system ground test created a false airborne target that generated a TCAS resolution advisory (RA) to an airliner on approach. “Pilot reaction to this RA required unnecessary maneuvering in congested airspace and initiated ATC re-sequencing actions that affected multiple aircraft and negatively impacted operations in the area for about 30 minutes.”
The FAA advises repair stations and maintenance personnel performing transponder and ADS-B systems testing to evaluate the adequacy of their methods and adhere to proper test procedures, including antenna shielding, to prevent propagation of test signals that could affect ATC operations or airborne aircraft. Theagency also recommends that maintenance personnel be aware of any local requirements to alert ATC of impending testing and review guidance contained in relevant advisory circulars.