FAA Policy To Provide Relief During ADS-B Outage

 - July 1, 2019, 12:15 PM

The FAA is assuring operators that, in certain circumstances, a degradation of GPS performance will not be deemed as noncompliance with ADS-B Out requirements, including cases where the properly-equipped operators conduct “due diligence.”

“There are circumstances outside of an operator’s control that may result in a temporary degradation of GPS performance and an apparent violation of [ADS-B] requirements,” the agency said in a new policy statement and outlined some of these circumstances.

An operator might perform due diligence before a flight to ensure the availability of ADS-B service for an intended route, but experience a rerouting that results in encountering an unanticipated degradation of performance. Further, an operator might encounter GPS interference along the intended path or be unable to complete a preflight check of availability because the FAA’s tool for such a check, the service availability prediction tool (SAPT), is out of service, the agency noted, and said it “will not consider these events to constitute noncompliance…due to the circumstances.”

To take effect Jan. 1, 2020, FAA rules require aircraft operating in controlled airspace be equipped with ADS-B Out technology that provides real-time positioning information. All approved ADS-B Out position sources rely on a GPS receiver.

To date, the FAA said the Wide Area Augmentation System (WAAS) is the only GPS position source that is consistently equivalent to radar, while noting that other position sources, such as Selective Ability-On (SA-On) or SA-Aware are more likely to experience performance outages.

The FAA developed the SAPT ADS-B service preflight prediction tool to provide the ability to meet positioning requirements and evaluate backup surveillance in areas where ADS-B outages are predicted. Trade association Airlines for America in 2015 received an exemption to permit operations when the GPS position information provided to installed ADS-B equipment does not achieve the required accuracy. Under the exemption, operators of aircraft with SA-On receivers must run a preflight prediction, either using SAPT or another tool. Operators equipped with SA-Aware are not required to conduct the preflight prediction under the exemption.

For SA-On/SA-Aware-reliant operations not covered under the exemption, the pilot-in-command must conduct due diligence to confirm that a planned route will comply with ADS-B performance requirements. Operators can use any reliable preflight prediction tool in these cases, but the FAA emphasizes SAPT provides a comprehensive and reliable preflight prediction.

Despite the predictive tools, GPS degradation could still happen in cases where this due diligence was conducted, the FAA said. Or the SAPT might encounter an outage or there may be GPS interference along the route, the FAA said. “Although it could appear that an operator has not complied with the performance requirements…due to circumstances described in this document, the FAA would not consider these situations to constitute a violation as such an application.”

In cases where an operator’s planned route changes, the FAA said, “After an ATC route clearance is obtained for the flight, the FAA does not expect an operator to conduct a subsequent preflight availability prediction to accommodate rerouting caused by ATC or environmental conditions.”

However, the agency warned that operators notified of consistent and repeated ADS-B Out performance issues would be considered to be in violation if they didn’t act to correct the issue.