As the Boeing 717-200 (B717) aircraft was levelling off in cruise flight at flight level 250, the crew noticed a 'MAP FAIL' message on the co-pilot's navigation display. This was followed by the same message on the pilot in command's (PIC) display along with a flight management system (FMS) double failure indication. After a short pause to allow the versatile integrated avionics (VIA) units to stabilise, the PIC selected 'STBY NAV' and reverted to the aircraft's very high frequency omni-directional radio (VOR) system for navigation.
The co-pilot then noticed that his FMS had become available once again; however, the flight plan information had been lost and required reloading. The PIC's FMS also became available and was re-instated. The flight then continued to Melbourne with no further anomalies.
A subsequent maintenance check of the aircraft revealed that both VIA units had indicated software faults. The aircraft had recently undergone a system software upgrade. The upgrade had been installed to prevent software faults that had resulted in previous FMS failures on this aircraft type. The aircraft's avionics system manufacturer was informed of the failure.
FMS reset
The software manufacturer advised that the loss of the FMS function (known as a reset) occurred under certain conditions when a secondary flight plan had been entered into the FMS. The normal procedure was to copy the primary flight plan to the secondary so it could be utilised for late changes once en route. However, if altitude adjustments during the flight were made using the altitude setting function on the autopilot glare shield controller, with the system selected to the EDIT mode, the primary flight plan data of the FMS would be updated automatically, but the secondary flight plan data would not. This would have created a conflict between the primary and secondary flight plans resulting in an FMS reset.
FMS software upgrade
The aircraft was fitted with the latest FMS software upgrade (VIA-905), which had addressed previously encountered problems associated with the system, and provided a number of improvements to the aircraft's operation. Although a dual reset resulting from the use of a secondary flight plan was experienced, the upgrade did allow the FMS to be reinstated after a built-in test equipment (BITE) test had been conducted.