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Maintenance: Problematic ADS-B Configuration Errors

Thousands of automatic dependent surveillance-broadcast (ADS-B) installs have been completed in compliance with the FAA’s mandate. Despite this track record, in the first six months of 2020, more than 9% of ADS-B installations triggered failure notices when operating in the national airspace system – and those failures were due to “installation errors,” not equipment problems. While that number has since fallen to around 5%, it still represents a significant discrepancy.

“Imagine a 5% systematic failure on a specific aircraft,” said Rick Ochs, CEO of Spirit Aeronautics. “We’d see airworthiness directives flying out of [Washington] DC.”

Ochs asserts that much of the fault lies in the FAA’s own guidance, including a 2017 policy letter that laid out “an incredibly complicated” certification path for ADS-B installations, which involve pairing an ADS-B-compliant transponder with a WAAS-capable GPS.

Per guidance outlined in Advisory Circular 20-165B, FAR 43 Appendix F and FAR 91.227, approval of an ADS-B installation is based on a successful ground test of that pairing before the aircraft is released back to the operator. Installations for one aircraft type are approved via supplemental type certificate (STC) on different aircraft using the same equipment.

That can set the aircraft maintenance technician (AMT) performing the installation up for failure. “There may be 100 configuration settings, and any one of those that is misconfigured will trigger an error,” Ochs said. “If the install was approved for a Falcon 50, but the AMT is now installing it on a Hawker 1000, they must complete a complex puzzle.”

“These regulations need to be rewritten. Cancel the [2017] policy letter and come out with new instructions for continued airworthiness.”

Rick Ochs CEO, Spirit Aeronautics

Furthermore, neither the operator nor AMT will know that error exists until ATC sees the misconfiguration as the aircraft flies in ADS-B airspace. NBAA Maintenance Committee Chairman Emeritus Greg Hamelink experienced this firsthand after an ADS-B installation prior to the 2020 mandate.

“One field listed the aircraft serial number instead of the N-number,” said Hamelink. “It was a relatively simple fix for our MRO, but we had no idea there was an issue until I received a letter [of investigation] and phone call from the FAA.”

A significant overhaul of the ADS-B process is needed, Ochs emphasized, beginning with the FAA policy letter and current ADS-B STCs that are tied to an “engineering process” and not to specific aircraft types.

“To my knowledge there’s not another STC that isn’t tied to an actual aircraft,” he said. “That creates unforeseen challenges that are now becoming evident.”

Ochs also believes current guidance must be changed to reflect hardware changes in case ADS-B-related equipment needs to be sent in for servicing. When shipped back to the AMT, the part may carry a revised part number reflecting any modifications, which technically no longer complies with the STC.

“These regulations need to be rewritten,” Ochs declared. “Cancel the [2017] policy letter and come out with new instructions for continued airworthiness, allowing repair stations to perform and certify ADS-B installations.”

In the interim, Hamelink recommends operators perform thorough due diligence when finding an MRO familiar with ADS-B installations on their specific aircraft type. “They need to know where these potential pitfalls are.”

Review NBAA’s ADS-B resources at nbaa.org/adsb.

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