When the FAA’s ADS-B Out regulation becomes effective next year, operators will need to predict the availability of the GPS constellation along their planned route and comply with a number of operational stipulations the FAA has outlined in its newly published policy on pre-flight performance requirements.
The new policy comes six months prior to the Jan. 1, 2020 ADS-B Out airspace mandate taking effect. Under the new policy, the FAA is requiring operators to assess how their aircraft’s position-reporting avionics will perform along their filed flight plans.
In the pre-flight planning process, the FAA is requiring pilots to use a preflight availability prediction tool to asses whether or not their aircraft’s GPS receivers can meet the navigation integrity category (NIC) performance requirements outlined by the technical standard order used by the agency to define the accuracy of position reporting equipment. NIC refers to the containment radius around an aircraft’s reported position, which must be accurate within less than 0.2 nautical miles of its actual airborne position.
Under the new policy, the FAA is specifically targeting operators of aircraft GPS receivers that are not wide area augmentation system (WAAS) compatible. WAAS was the first operational Satellite-Based Augmentation System (SBAS), some avionics manufacturers use the term “SBAS receivers,” according to an emailed statement from the FAA. Operators who equip with non-WAAS receivers are more likely to experience performance outages that limit their access to the airspace defined in the rule.
When assessing the GPS performance for their intended flight plan, if an operator determines that the predicted performance will not support the proposed flight, the FAA will require the pilot to adjust the route to avoid the area where degraded performance could occur.
An ADS-B Out failure message. Photo: Universal Avionics Corp.
“After an operator receives a satisfactory preflight availability prediction for an intended operation, there may be certain conditions that warrant a subsequent prediction. For example, a change in departure time or a change in the GPS satellite constellation as indicated by a Notice to Airmen (NOTAM) may have an effect on the predicted GPS performance for the intended operation,” the policy statement said.
There is also an acknowledgement by the FAA regarding its Exemption 12555 policy, a one-time grant of exemption for aircraft from 14 CFR § 91.227 requirements for operators using GPS receivers when their performance falls below the requirement and backup surveillance is unavailable. The FAA established that exemption to address the performance characteristics associated with the three different variants of GPS receivers that are currently found in air transport category aircraft.
"The exemption allows for the extended use of an older type of GPS navigation receiver already installed in some aircraft with a strict, limited timeframe in which operators must equip with new navigation receivers. All other ADS-B Out equipment requirements must still be met and operational by January 1, 2020," a representative for the FAA said in an emailed statement.
Some operators that have qualified for Exemption 12555 do not need to perform a preflight availability prediction. Exemption holders with SA-On receivers and those who fall outside of the exemption and are flying aircraft with GPS receivers that may meet the necessary NIC and NAC performance requirements must use either their own preflight availability prediction tool or the FAA’s Service Availability Prediction Tool (SAPT).
Additionally, when pilots receive NOTAMS indicating that planned government GPS interference testing impacting ADS-B Out airspace occurs, they will not require operators to avoid that airspace. A technical evaluation of such occurrences by the agency determined that they have no way of guaranteeing whether an aircraft flying through affected airspace would actually experience GPS performance degradation.
The latest ADS-B Out equipage levels as reported by the FAA. Photo: FAA
The new pre-flight policy is the latest in a series of new guidelines established by the FAA to help airspace users transition from relying on ground-based radar to ADS-B as the preferred air traffic surveillance source in the U.S. In April, a new policy for non-equipped aircraft was published noting that air traffic controllers will only approve non-ADS-B flights when traffic permits. Avionics manufacturers and installation facilities have also been working to ensure operators know how to deal with ADS-B failures.
As the 2020 mandate draws closer, the commercial airline segment of the U.S. flying community appears to be on track to have nearly all of their aircraft requiring upgrades equipped. The general aviation community remains the lowest equipped segment, with the U.S. registered helicopter fleet remaining the lowest equipped segment.
Correction: This article has been updated to properly identify WAAS receivers, which some avionics manufacturers may describe as 'SBAS receivers,' as well as to clarify the FAA's Exemption 12555 policy and its policy on allowing non-ADS-B equipped flights only when traffic permits them.