Boeing Co 717-200, VH-VQE

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.