Software Anomaly In GNS Navigation Systems

The FAA has issues a Special Airworthiness Information Bulletin (SAIB) for all modification levels of Honeywell GNS Series Navigation Systems: GNS_XLS PRNAV, part number (P/N) 17960-0103-XXX; GNS_XLS Enhanced PRNAV, P/N 17960-0204-XXX; and GNS_XL PRNAV, P/N 18355-0102-0XXX. 

Honeywell has recently discovered a software anomaly in their GNS Navigation Systems. This anomaly may affect the area navigation (RNAV) procedures, which contain RF (Radius-to-a-Fix) legs. If an RNAV procedure containing RF legs is loaded into the flight plan with the navigation system being used to fly the full procedure, the GNS system could fail to capture and fly the RF leg curved path and continue past the waypoint on an undetermined track line. It should be noted that the GNS PRNAV systems are not approved for RNAV Required Navigation Performance (RNP) procedures. Honeywell Service Information Letter (Publication Number D201003000024) has been issued.

The FAA recommends that pilots using these systems adhere to the following:

• Do not load any approach or departure procedure listed in Table 3 of the above-referenced Service Information Letter.
• Do not load any approach or departure procedure listed as Special Aircraft & Aircrew
• Authorization Required or Special Authorization Required printed on the aeronautical chart.
• Do not load any approach or departure procedure requiring RF capability.
• Refer to the above-referenced Service Information Letter for additional guidance.

The administration has determined that the situation does not require the issuance of an AD at this time.

FMI: www.faa.gov