ADS-B may function as a Traffic Alerting system, but..... Curt Lewis

FAA announces changes to TIS-B
By Elizabeth A Tennyson

The FAA is preparing to implement changes to its Traffic Information Services-Broadcast (TIS-B), which provides traffic information to aircraft using Automatic Dependent Surveillance-Broadcast (ADS-B) Out and In.

The changes first announced in early 2015, which are scheduled to take effect in Southern California beginning in mid-January with nationwide implementation completed by late February, are designed to ensure that aircraft carrying certified ADS-B In equipment can "see" additional traffic. The changes also eliminate any incentive for operators to equip with ADS-B Out systems that are not compatible with certified ADS-B In systems.

"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."

Currently, aircraft emitting ADS-B Out signals that do not comply with the performance requirement of any FAA standards are invisible to aircraft receiving TIS-B information through a certified ADS-B In system. That's because certified ADS-B In systems filter from the display targets that don't meet certain quality parameters in the ADS-B message (see the link above for details). As a result, aircraft that may have improperly installed ADS-B Out systems or those with non-certified ADS-B Out systems are invisible to aircraft with properly functioning certified ADS-B In systems.

The FAA estimates that its planned changes will make an additional 2,000 aircraft visible to aircraft with certified ADS-B In systems. This issue also highlights that a large number of aircraft have ADS-B Out but the avionics do not meet the requirements of the FAA's 2020 rule. Pilots can determine if their ADS-B Out system meets the FAA's standards for free by contacting the FAA which will look at previous flight data to see if the aircraft was sending the proper signals.

For aircraft with "non-performing" ADS-B Out that also use an ADS-B In system, or for operators using some portable ADS-B In systems, the change will mean that their own aircraft may appear as traffic on their display, a phenomenon known as "ownship ghosting." A similar phenomenon called "target ghosting" can occur when an ADS-B In system receives both TIS-B and ADS-B information for the same target aircraft and displays both as if they were separate aircraft. Ghosting, which will be far more common with aircraft having "non-performing" ADS-B Out, has the potential to create confusion for pilots or trigger proximity alarms in some systems. Some manufacturers, including Garmin, have implemented software updates that they believe will prevent users from experiencing ghosting. Other manufacturers, including Appareo which makes Stratus, have created help pages on their websites to advise users about how to prevent ghosting.

The TIS-B service, derived from transponder replies to ATC radar, is currently designed for "client" aircraft equipped with both ADS-B Out and ADS-B In. Aircraft carrying ADS-B In equipment receive data directly from nearby aircraft with ADS-B Out on the appropriate frequency (1090 MHz or 978 MHz). Those using only ADS-B In equipment (no ADS-B Out) may receive incidental TIS-B information, which could result in an incomplete traffic picture because this TIS-B information was optimized for a different "client." The traffic picture is in the shape of a hockey puck which is designed for the client aircraft, not the ADS-B In only aircraft. As a result, aircraft with only ADS-B In equipment may not receive traffic information that is relevant as it may be outside the "client's" hockey puck.

In the meantime, AOPA continues to make safety and the availability of traffic information to every pilot a top priority. AOPA has responded to our member's requests and continues to advocate for all relevant TIS-B (traffic) data to be broadcast to any aircraft with ADS-B In, including to users with only portable ADS-B In systems. The association made its most recent formal request in October, and has been working with the FAA and industry through the Equip 2020 working group to make this much needed safety enhancement a reality.

"At AOPA 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 AOPA's 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."

While TIS-B has limitations-it is only intended to serve as a transitional system in radar airspace while ADS-B is fully implemented and in some places traffic information updates only every 13 seconds because of radar latency, making traffic difficult to track-the benefits of allowing more pilots access to the data are clear, said Melissa Rudinger, AOPA vice president of government affairs.

"When the regulation was written, technologies that are now commonplace, like tablet computers, did not yet exist," said Rudinger. "We're asking the FAA to update its rules to reflect the realities of the way people are flying now and provide a continuous uplink to give more pilots the situational awareness and associated safety that TIS-B can deliver."

At the same time, she warned, pilots will need to install ADS-B Out in their aircraft in order to realize the full benefits of NextGen modernization.

"Since so many pilots are already flying with iPads and other equipment that will allow them to receive TIS-B information, it just makes sense to make that information available to them," Rudinger said. "In the meantime, we're urging aircraft owners who fly where a Mode C transponder is now required as well as those who want to enjoy the full benefits of air traffic modernization to go ahead and equip ahead of the FAA's 2020 ADS-B Out mandate."

The FAA reports that as of Dec. 1, 2015, 15,318 general aviation aircraft were equipped for ADS-B Out compared to approximately 160,000 GA aircraft that carry transponders. The agency says it has completed all the needed software changes to make all en route and large tracon facilities ADS-B compatible and is on schedule have all air traffic automation used to assist with separation ADS-B capable by 2020.

Elizabeth Tennyson
Elizabeth A Tennyson | Senior Director of Communications, AOPA
AOPA Senior Director of Communications Elizabeth Tennyson is an instrument-rated private pilot who first joined AOPA in 1998.