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Is Your ADS-B ‘Out’ Doing Things Right?

By Clif Stroud, FAA NextGen Performance and Outreach

July 25, 2017 - FAA data show that about 6,000 of the 36,000 ADS-B “out” installations completed so far have performance problems or transmit incorrect data. Most of the aircraft with issues are single-engine general aviation aircraft.

James Marks, with the FAA’s Flight Standards Service Aircraft Maintenance Division, is the ADS-B Focus Team leader, and he’s working hard to help cut down on installation errors.

“The three most serious errors that we regularly see are transmission of a wrong ICAO code, an incorrect flight identification or call sign, and dual ‘out’ boxes using different ICAO codes,” James said.

ADS-B has an FAA-assigned 24-bit ICAO code. This code is different from the flight identification, which should match the aircraft’s N-number. The installation technician must enter this information to comply with the rule — and glitches do occur. One of the ADS-B Focus Team’s highest priorities is to promptly contact any aircraft owner with incorrect ICAO codes or flight identification. The FAA handles about 200 of these cases each month. Call sign mismatch is a related issue for aircraft using a call sign instead of an N-number. This isn’t an issue for the majority of general aviation operators, but for those who file flight plans using variable call signs, such as “lifeguard,” they will need equipment that allows call sign entry.

The third issue is a twist of technology. When the ADS-B rule was first proposed, the idea was aircraft would have to equip with either a Mode S transponder (operating on 1090 MHz) or a universal access transceiver or UAT (operating on 978 MHz). Both meet the requirement for an ADS-B transmitter. To ensure that an aircraft is seen in all airspace — even outside FAA ADS-B coverage — some aircraft owners are equipping with both device types. This approach can result in a “dual out” problem.

“If the ICAO code in your Mode S transponder — reporting to the ground on 1090 MHz — and your UAT avionics — reporting on 978 MHz — are different, your aircraft may appear on a controller’s display as two aircraft in close proximity,” James explained. “Also, if your aircraft is equipped with ADS-B “in,” you may see a second aircraft displayed very close to your own position, prompting you to try to avoid an aircraft that isn’t there.”

The ADS-B Focus Team is also aware of a reporting issue called air/ground determination. The FAA has detected ADS-B-equipped aircraft reporting in airborne mode while taxiing or stationary. This problem stems from issues with the ADS-B avionics that make the actual air/ground determination and relay that information to the FAA’s ADS-B system. The FAA is working with avionics manufacturers to better understand the issue and determine how to resolve it.

“We emphasize making sure your installation is compliant with the rule before signing off on work, because many aircraft equipped with ADS-B are operating with some type of unresolved problem,” James said.

To make sure everything is good, make certain your installer uses ground-based testing equipment. Such equipment will detect most issues, but the ultimate test is to fly an aircraft in ADS-B rule airspace and request a performance report. The FAA can provide that report for free, usually within 30 minutes of a flight. You can request your report here: ADSBPerformance.FAA.gov/PAPRRequest.aspx.

The performance report will tell you what, if anything, needs to be corrected. That will help you figure out who needs to fix it. In most cases, the answer is your avionics shop. ICAO codes and Flight ID are set by the installer, and any conflict between 1090/978 MHz outputs should also be corrected by the installer.

An air/ground determination failure is more complicated. Inspection by an installer is a good first step, but the culprit could also be an issue with the avionics. If the installer verifies that everything else is correct, you will need to go to the equipment manufacturer. If this source is unable to resolve the situation, please contact the FAA via e-mail at 9-AWA-AFS-300-ADSB-AvionicsCheck@faa.gov to request a review. This communication should include “PAPR Review Request – Air/Ground Failure” in the subject line, and attach a copy of your performance report.

The FAA has prepared a user’s guide to help operators understand what the ADS-B Performance Report means. The guide — available at ADSBPerformance.FAA.gov/PAPRUsersGuide.pdf — explains what each section of the report is measuring. The performance report or the opportunity to generate one is a sound means to verify correct installation work.

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