CERTIFICATION APPROVAL: TSO Authorization (see Approval section of SB1379 for details)
COMPLIANCE
Mandatory
PURPOSE
If the GNC 255 RS-232 Serial Port is configured to output ‘NMEA’ data, the CDI on an EFIS/PFD using this data will deflect in the wrong direction when the GNC is tuned to a VOR and the TO/FROM flag indicates FROM. Additional information is contained in Service Alert 1380.
Note: This issue does not affect G500/G600 installations that are configured to use the ‘SL30’ RS-232 interface to communicate with the GNC 255.
Note: This issue is most prevalent in experimental amateur built (EAB) and light sport aircraft (LSA) aircraft using experimental EFIS/PFD systems since the RS-232 NMEA interface is typically used in these installations.
For installations that have an EFIS/PFD system, pilots should contact their Garmin dealer for more information. Customers that have experimental EFIS/PFD systems connected to the GNC 255 via the RS-232 NMEA interface can contact Garmin Aviation Product Support for a copy of the Service Bulletin 1379.
PRODUCTS AFFECTED
All GNC 255 series units with Display Software Version 2.01 that are connected to an external EFIS/PFD, excluding G500/G600 systems, are affected.
DESCRIPTION
This mandatory service bulletin provides instructions to disable the RS-232 NMEA interface from the Serial Port on GNC 255 units with Display Software Version 2.01.