P&E: ADS-B

TIS-B changes to make more traffic visible—for most

The potential for pilots of properly equipped aircraft to see position information on more traffic is the primary benefit of a change that the FAA is making to one aspect of the Automatic Dependent Surveillance-Broadcast system. ADS-B, which uses satellites instead of ground-based radar to determine aircraft location, is a key technology behind the FAA’s Next Generation Air Transportation System. The FAA has mandated ADS-B Out equipage beginning January 1, 2020, for operations in most airspace where a transponder is required today.

The changes will make an estimated 2,000 additional aircraft visible to pilots flying with certified ADS-B Out and In equipment, according to the FAA. They also eliminate any incentive for aircraft owners to equip with unapproved ADS-B Out systems, which will no longer trigger aircraft-specific traffic information. Announced in March 2015, implementation of the changes began in January and nationwide completion was anticipated by late February.

“By making these changes, the FAA is closing a gap that has made some traffic invisible,” said Rune Duke, AOPA director of airspace and air traffic. “While this is an important step that can help improve traffic awareness, pilots need to remember that they still have a responsibility to be vigilant, look outside, and maintain separation from other aircraft.”

Showing more traffic

From the FAA’s perspective, there are three levels of performance—based on the quality of the required Wide Area Augmentation System (WAAS)-enhanced GPS position information—that it considers with respect to ADS-B Out. If the position information is not good enough, it will not display on any certified ADS-B In system. Some position information is good enough for display but it is not suitable to be used for separation of traffic. Examples of this second level include the earlier Version 1 ADS-B avionics used during the Capstone Program in Alaska, and on a very limited basis in the lower 48 states. Finally, there’s position information that is good enough for separation; generally, this equipment complies with the January 1, 2020, FAA requirement.

According to the FAA, data transmitted by 15 percent to 40 percent of the aircraft equipped with ADS-B Version 2 hardware actually identifies them as having less accurate GPS position information. This could be the result of hardware configuration issues, the FAA said. These aircraft show up in the lowest performance level, and are not displayed as traffic to other ADS-B-equipped aircraft—although their ADS-B Out does allow them to receive ADS-B In traffic information. The same things happen to aircraft equipped with unapproved ADS-B Out equipment.

As a refresher, in airspace where ADS-B traffic information is available, an aircraft properly transmitting ADS-B Out data—and equipped with ADS-B In capabilities—should receive information from ground stations on traffic within a 30-nautical-mile-diameter cylinder centered on the aircraft, and extending 3,500 feet up and down. Because of its shape, this coverage area often is dubbed the ADS-B Out aircraft’s hockey puck. This applies to both Traffic Information Service-Broadcast (TIS-B provides ADS-B Out/In-equipped aircraft with the positions of transponder-equipped, non-ADS-B aircraft operating in areas of radar coverage) and Automatic Dependent Surveillance-Rebroadcast (ADS-R relays ADS-B Out information transmitted by an aircraft on one of the two ADS-B datalinks to aircraft equipped with ADS-B In on the other link). An aircraft with ADS-B In will receive traffic information on its ADS-B frequency directly; the hockey puck affects only information sent from ground stations.

The FAA’s changes to the TIS-B Target Status logic means that position information for all ADS-B Out-equipped aircraft—including those with less accurate GPS position information or unapproved ADS-B Out hardware—will be visible to all ADS-B In systems installed on aircraft with certified ADS-B Out hardware.

Seeing less traffic

Another system change will prevent targeted traffic information from being sent to unapproved—as well as misconfigured—ADS-B Out units. Essentially, the FAA is establishing a minimum requirement for ADS-B Out units to receive targeted TIS-B and ADS-R traffic information within that aircraft’s hockey puck.

Now ADS-B Out hardware will have to meet the requirements of Technical Standard Order C199 in order to receive that benefit, which the FAA says “will eliminate the current incentive for operators to equip with ADS-B Out systems that are not compatible with certified ADS-B In systems.” (TSO-C199 sets standards for Traffic Awareness Beacon Systems, intended as a low-cost surveillance solution for balloons, aircraft without electrical systems, and other aircraft excepted from transponder and ADS-B Out requirements.)

That means aircraft with unapproved ADS-B Out hardware, like those equipped only with portable ADS-B In systems, will not receive a complete traffic picture (see “Technology: Who’s Seeing Whom?” July 2014 AOPA Pilot).

Because safety and the availability of traffic information to every pilot is a top priority. AOPA continues to advocate for all relevant traffic data to be broadcast to any aircraft with ADS-B In—including those with only portable ADS-B In systems. The association made its most recent formal request in October 2015, and continues to work toward this goal with the FAA and industry.

“We encourage every pilot to equip with ADS-B Out, but feel strongly that TIS-B traffic information should be available to all pilots, not just those who have purchased ADS-B Out equipment,” said George Perry, senior vice president of the AOPA Air Safety Institute. “Currently, portable receivers only allow for a partial, incomplete traffic picture. We want to change that and help provide a more complete picture of traffic to everyone, even pilots flying with portable TIS-B receivers and an iPad.”

If your aircraft is equipped with ADS-B Out and you recently realized that you’re seeing less traffic on your ADS-B In equipment, it’s possible that your Out hardware is misconfigured.

Aircraft owners can request a free evaluation of their ADS-B Out system’s performance by Emailing the FAA’s Compliance Monitor ([email protected]) with the N number; ADS-B transmitter and GPS make and model numbers; and date, location, and approximate local time of a recent flight to find out if your equipment is working properly. We’ll talk more about this service in a future issue.

Email [email protected]

See AOPA’s online ADS-B resources and ADS-B selection tool.