In its comments to a proposed airworthiness directive (AD) that would require the removal of certain NavWorx universal access transceivers (UATs) from an estimated 800 general aviation aircraft, AOPA recommended that the FAA provide additional information on the UATs’ reported deficiencies, as well as greater clarity on the necessity of the proposed AD. The affected UATs provide an Automatic Dependent Surveillance-Broadcast (ADS-B) datalink on the 978-MHz radio frequency, giving aircraft ADS-B Out and In capabilities.
ADS-B uses GPS satellites instead of ground-based radar to determine aircraft position, and is a fundamental technology behind the FAA’s Next Generation Air Transportation System, or NextGen. The FAA has mandated ADS-B Out equipage for operations after Jan. 1, 2020, in any airspace where a transponder is required today.
The FAA issued an unapproved parts notification Oct. 14 affecting NavWorx UATs with part numbers 200-0012 and 200-0013. The agency followed up Oct. 20 with the proposed AD, which would require removing the UATs from the aircraft in which they have been installed; the notice of proposed rulemaking also added NavWorx’s non-technical standard order ADS600-EXP UAT with part number 200-8013. The FAA suspended the company’s technical standard order authorization for the affected TSO'd UATs on Nov. 21 after NavWorx reportedly declined on repeated occasions to allow the FAA to conduct required inspections.
The FAA has expressed concern that the affected UATs may contain an internal GPS receiver that does not meet the FAA’s minimum ADS-B performance standards. NavWorx ADS-B transceivers with part numbers 200-0112 and 200-0113 contain a different WAAS GPS position source and are not subject to the proposed AD or any of the FAA’s other regulatory actions.
“To eliminate confusion and concerns, the FAA should address whether the internal GPS position source in the NavWorx ADS-B UAT met the applicable performance requirements during certification,” Barkowski said. “The FAA should explain with greater descriptive clarity how emitting an incorrect SIL value constitutes an unsafe condition which may lead to an aircraft collision.” He also said the FAA should clarify why the non-TSO'd UAT, intended for use in experimental and light sport aircraft, is included in the proposed AD.
AOPA also asked the FAA to clarify the meaning of “uncertified GPS source,” as used in the notice of proposed rulemaking proposing the AD, as well as whether the FAA intended to apply the proposed AD to experimental category aircraft.
“If the proposed AD is necessary, AOPA believes the FAA should amend the proposed corrective action to minimize the economic impact on owners,” Barkowski wrote in AOPA’s comments, noting that the FAA’s $85 estimated cost of compliance does not include the cost of purchasing and installing another ADS-B Out system to comply with the 2020 mandate. AOPA encouraged the FAA to allow continued used of the UATs if the system uses an approved external position source, and not the integrated GPS; if NavWorx updates its software, returning the UATs’ SIL to the previous value; or if NavWorx upgrades the internal position source with one that meets the FAA’s requirements.
NavWorx has indicated that if the FAA implements the proposed AD, it will offer upgrades to a different position source. “If the FAA does not allow the use of the internal GPS, then we will offer the ability to modify the products from the 200-0012 and 200-0013 part numbers to part numbers 200-0112 and 200-0113,” said NavWorx President Bill Moffitt.