Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
AIR-22-07
April 6, 2022
This is information only. Recommendations
aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin (SAIB) is to inform
owners and operators of aircraft equipped with Avidyne Corporation
(Avidyne) DFC90 autopilots coupled with Avidyne primary flight displays
(PFDs) and Garmin global positioning system (GPS) and GPS navigation
systems (GNS) navigators of a potential uncommanded turn to heading 360
if SBAS, EGNOS, MSAS/QZSS, or GAGAN WAAS reception is lost during an
autopilot coupled non-degradable localizer performance with vertical
guidance (LPV) approach.
At this time, the airworthiness concern is not an unsafe condition that
would warrant airworthiness directive (AD) action under Title 14 of the
Code of Federal Regulations (14 CFR) part 39.
Background
The anomaly was discovered in simulated flights during student pilot
training by Orbify, an ASA IFR training company affiliated with the
Federal Aviation Administration (FAA) and European Union Aviation
Safety Agency. When performing non-degradable LPV approaches simulating
loss of SBAS reception, the Avidyne autopilot made an uncommanded turn
to heading 360.
Avidyne investigated and was able to reproduce this anomaly. During the
scenario described above, the Avidyne autopilot receives an unexpected
output from the GNS navigator. The GNS navigator discontinues approach
guidance but continues to indicate that it is in approach mode. GPS
roll steering commands are suppressed, and the PFD and autopilot, in
combination, revert to the numerical heading value being transmitted,
which is 360.
The investigation revealed the affected configurations are Avidyne
DFC90 autopilots with software part number (P/N) 510-00874-000 Rev03 or
earlier, coupled with Avidyne PFD P/N 700-00006-XXX with software P/N
530-00214-002 Rev06 or earlier, and Garmin GNS430/530W or GTN650/750
navigators.
Avidyne released Service Information Letter (SIL) 606-00170-004, Revision 00, dated December 14, 2021, regarding this issue.
Recommendations
The FAA recommends that all owners and operators of aircraft with
affected autopilot, PFD, and navigators review the contents of Avidyne
SIL 606-00170-004, Revision 00, dated December 14, 2021, and follow the
applicable Recommended User Actions.
For Further Information Contact
Nick Rediess, Aviation Safety Engineer, Boston ACO Branch, FAA, 1200
District Avenue, Burlington, MA 01803; phone: (781) 238-7159; email:
nicholas.rediess@faa.gov.