FAA Warns of ADS-B False Alerts

Test signals emanating from the ground have triggered TCAS alerts in airborne aircraft.

ADS-B false alerts
The FAA recently warned of adhering to proper testing procedures for any new ADS-B equipment based on problems that have begun appearing.FAA

As the countdown continues to the Dec. 31, 2019, deadline for ADS-B Out installation, the pace of updates is expected to increase significantly and the agency is concerned about shops rushing to complete the required work.

The FAA, in a safety alert for operators (No. 17002), recently warned of adhering to proper testing procedures for any new ADS-B equipment based on problems that have begun appearing. The agency mentioned reports of transponder and ADS-B Out system ground tests in which information, including simulated altitude, was erroneously transmitted from a test aircraft on the ground and received by aircraft in flight.

In at least one instance, a ground test created a false airborne target that generated a traffic alert and collision avoidance System II (TCAS II) resolution advisory to a Boeing 737 aircraft on approach to a congested airport. While the pilot correctly reacted to the event, ATC was required to re-sequence other arrivals causing considerable delays.

The FAA says equipment ground tests obviously involve a check of the aircraft’s altimetry system to simulate operation at various altitudes. But if transmission lines are not correctly attached to the test equipment, antenna shielding must be used to prevent signal interference with nearby ATC operations or TCAS-equipped aircraft. The agency recommends repair stations evaluate their ability to prevent random signal transmission while adding that in some cases, local requirements might demand notifying ATC of any impending equipment testing.