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.
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.
The double failure of the FMS was consistent with that experienced as a result of primary and secondary flight data conflict. Having the upgraded software fitted to the aircraft allowed the re-instatement of the flight management system following successful completion of its BITE procedure. As the FMS was capable of functioning normally without the use of a secondary flight plan, the dual reset under those conditions was not considered critical.
As a result of this occurrence, the operator has issued a Flight Operations Memo advising all B717 pilots that: " Effective immediately, discontinue the use of the secondary flight plan during operations".
As a result of this occurrence, the aircraft manufacturer has:
- Released a Flight Operations Bulletin, B-717-02-001 on 7 March 2002, describing the conditions that may result in a dual FMS failure and suggested flight crew response.
- Scheduled a system software upgrade (VIA-907) addressing this issue which is due for release in 2003.
|Date:||08 December 2001||Investigation status:||Completed|
|Time:||2025 hours ESuT|
|Location:||30 km N Launceston, Aero.|
|Release date:||08 November 2002||Occurrence category:||Incident|
|Report status:||Final||Highest injury level:||None|
|Aircraft manufacturer||The Boeing Company|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Nil|
|Departure point||Launceston, TAS|
|Departure time||2010 hours ESuT|