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What’s Next for ADS-B in the US Air Traffic System?

An updated look at the latest ADS-B related challenges and opportunities that the FAA is working on with airlines.

Now that the FAA’s ADS-B Out airspace mandate has been in place for well over a year, the U.S. air traffic system’s new primary surveillance medium has a Flight ID issue that the agency is addressing while collaborating with airlines and avionics manufacturers to develop new ADS-B In applications and version 3.

Now, the FAA’s focus with ADS-B is addressing the problem with Call Sign Mismatch (CSMM), where ADS-B Out transceivers on air transport and general aviation aircraft are broadcasting Flight IDs that do not match the aircraft’s ID or N-number that the pilot filed with the flight plan. Flight ID is one of 19 bits of information broadcasted by ADS-B transceivers, others include altitude, velocity, and position derived through GPS.

As part of an Aug. 5 webinar, James Kenney, an aviation safety inspector for the FAA, explained how the agency observed 2,293 CSMMs by GA aircraft transceivers during the month of May.

According to Kenney, there are three main causes of CSMMs, including the Flight ID field of the ADS-B transceiver being programmed incorrectly during installation.

Another common cause of Flight ID mismatch is the use of exotic call signs by organizations such as Angel Flight, Animal Rescue, or acrobatic and air show performance operators. Kenney said that after some of these flights, pilots can forget to re-program the Flight ID field for ADS-B. The third most common cause of CSMMs is associated with maintenance events.

“We’ve seen a number of maintenance events where the battery is disconnected, or where the power is taken off of the avionics where this causes the Flight ID field in the ADS-B transceiver to reset back to the manufacturer’s default settings,” Kenney said.

One of the causes of a call sign mismatch occurs when an aircraft undergoes maintenance and the power is disconnected from the aircraft, which can reset the ADS-B unit's Flight ID field back to factory settings, according to the FAA.NBAA

When asked whether CSMMs were also a problem for airlines, Kenney said the FAA is currently engaging airlines on the issue and have made some progress.

“It is a problem but it’s not anywhere near as big a problem as it used to be,” Kenney said. “Part 121 operators…really always use ICAO callsign Flight IDs, which means that they’re changing their flight number typically every flight or at least every other flight, so we do have a lot of changing going on. There was a tremendous amount of education that has taken place within the pilot community. “

Flight ID is not the only ADS-B issue being investigated by the FAA and operators, as the non-performing emitter (NPE) errors continue to occur as well. NPE is a term that refers to aircraft equipped with ADS-B Out that is not transmitting to the compliance requirements of FAR 91.227. One example of an NPE is when an aircraft transmits the incorrect value for its weight.

In April, the FAA changed the way it records NPEs for ADS-B transmissions on a per month basis, eliminating pilot or flight crew-related errors such as CSMMs.

“Using the new procedures, we are now able to include only those aircraft with likely ADS-B equipment issues (i.e., the ADS-B equipment installed on the aircraft is not meeting FAA required performance standards). The FAA is currently addressing aircraft with any ADS-B issue, either operational and/or equipment-related,” the FAA said in an emailed statement to Avionics International. “As of this date, we have not thoroughly investigated NPE differences among Universal Access Transceiver and 1090ES transmitters.”

Is ADS-B Providing Post-Mandate Airline Benefits?

If you ask most pilots of any aircraft type, as a surveillance source alone, ADS-B Out is not a major enabler of new flight operational benefits, although there are some that have been observed. One major upgrade that ADS-B brings to the National Airspace System is its expansion of surveillance to airports and areas of the U.S. where the FAA previously did not have substantial radar coverage.

As some airlines have expanded to new domestic destinations, the increased coverage and surveillance can prove to be beneficial. Southwest Airlines, for example, has its entire Boeing 737 fleet equipped with ADS-B Out transponders and recently added some new mountainous areas of Colorado to the number of destinations it flies to. While radio waves cannot penetrate mountains, ADS-B ground stations extend to those harder-to-reach areas.

“Keeping safety front and center, we’re seeing benefits from some of our newer destinations that do not have traditional radar coverages or air traffic services. A few examples are Steamboat Springs (HDN) and Telluride (MTJ) where Wide Area Multilateration (WAM) services are deployed. In HDN’s case, Denver ARTCC can actually see ADS-B-equipped aircraft taxiing on the ground. Regarding efficiencies, our ETOPS aircraft are approved for Performance-Based Communications and Surveillance, and we’re seeing its effectiveness with respect to our flights to and from the Hawaiian Islands,” Trey Turner, Southwest’s technical pilot and program manager for airspace and navigation told Avionics.

Southwest Airlines has its entire fleet equipped with ADS-B, including this 737 shown taking off from Denver International Airport. Denver International Airport

Some of the more near-term benefits can still seem invisible to pilots. Since its surveillance quality performs better and faster than radar, ADS-B can improve the prediction of short-term aircraft trajectories, according to the Air Line Pilots Association (ALPA).

"ADS-B has also proved useful in providing surveillance during radar outages. For example, during the FAA’s test of Space-Based ADS-B in Miami Air Route Traffic Control Center, FAA was able to continue to “see” aircraft in the Caribbean during an outage of a radar located in the Bahamas," a representative for ALPA told Avionics. "Without ADS-B, when this radar is out of service, the FAA is forced to use procedural separation, which reduces efficiency and increases safety risk."

Most flight operational benefits observed by the organization have come in oceanic areas featuring space-based ADS-B. As an example, ALPA noted in its responses how ADS-B data has been used to rescue pilots after a forced landing or crash because of its ability to provide aircraft position information to search and rescue personnel to the point where the aircraft touched down.

ALPA also expressed support for the use of space-based ADS-B in combination with Required Communications Performance being met to allow for increased reduction of separation required in oceanic airspace.

Version 3 and ADS-B In

Most industry experts believe that the next steps for ADS-B in terms of providing flight operational benefits to airlines will be derived from the use of ADS-B In on properly equipped displays. The Radio Technical Commission for Aeronautics (RTCA) Special Committee 186 has been tasked with standardizing the continued improvement and expansion of ADS-B as a surveillance source over the last decade.

Special Committee 186 most recent update for ADS-B includes publishing the Minimum Operational Performance Standards (MOPS) for 1090ES ADS-B Version 3.

"ADS-B Version 3 increases information available (e.g., weather information, spectrum monitoring, and airspeed), enables new wake turbulence applications, and enhances weather forecasting. ADS-B Version 3 also enables/enhances ADS-B In applications, such as Flight Interval Management. SC-186 is currently working on DO-282C, an update to the UAT MOPS for ADS-B Version 3. SC-186 is also planning to create a DO-260C Change 1 document, which will be limited in scope and is solely intended to address errors that have been found since the publication of DO-260C," according to the FAA.

American Airlines has become a leading U.S. carrier for the realization of ADS-B In benefits, as it has committed to equipping its entire A321 fleet with SafeRoute+, a line of flight deck displays designed to support ADS-B In manufactured by L3Harris. The upgrade process for the A321 fleet is ongoing.

The Safety Committee for the Allied Pilots Association (APA)—which represents American Airlines pilots—provided Avionics with an update on their involvement in introducing the use of an ADS-B Guidance Display that will serve as their pilots' primary instrument for ADS-B In generated traffic information.

"American pilots have been introduced to this new technology through training materials provided in various platforms within their iPad Electronic Flight Bag that includes Distance Learning Modules, a Fleet Bulletin, and Airbus A320 Crewcast (podcast) episodes -- all dealing with the ADS-B IN/OUT and upcoming capabilities and changes at American Airlines," APA told Avionics in an emailed statement. "As American continues to equip the fleet, pilots are encouraged to gain familiarity with the new tools and are free to conduct CAVS (CDTI Assisted Visual Separation) during scheduled flights. This experience will be valuable as Interval Management (IM) and other applications are demonstrated and deployed."

Interval management is an ADS-B In application that gives pilots more control over the spacing of their aircraft relative to other ADS-B equipped aircraft arriving at busy airports. The concept involves an air traffic controller contacting pilots of a particular aircraft, informing them of the spacing goal, the trajectory the aircraft should fly, and the ID of an aircraft ahead of them in order to provide an ideal amount of separation to aircraft on approach into an airport.

The pilots then enter all of this information into the FIM system, which then computes a solution with the additional help of input from the airplane’s ADS-B unit. The result is a number displayed on FIM screens for the pilots to see that tells them what speed to fly so they can follow the specified aircraft a safe distance in front of them all the way down to the runway.

American Airlines is equipping its entire Airbus A321 fleet with ADS-B In displays. This image shows a December 2019 flight test that American performed using L3Harris ADS-B In technology. L3Harris

“APA Safety Representatives were invited to provide direct input to the airline and L3Harris during the development of the new system, including interface with the avionics and feedback on the display and content of information from the ADS-B Guidance Display (AGD) that will be the primary instrument for ADS-B In traffic information,” a representative for APA said. “The Allied Pilots Association is proud to be part of the pioneering efforts of ADS-B In that can enhance safety for our pilots and provide a more efficient flight for our customers. We will continue to work side-by-side with the FAA, National Air Traffic Controllers Association (NATCA), and other aviation industry stakeholders as ADS-B In advances in the National Airspace System.”