We are focusing on the flight planning function of the FMS. The main objective of the flight planning function is to provide a means to construct a flight plan using the navigation database as well as user-specified information. Terminal area procedures (Standard Instrument Departures [SIDs] and Standard Terminal Area Routes [STARs]) are defined per the navigation database as published by the database supplier. These procedures are made up of waypoints that are defined by different leg types, such as an arc leg, heading legs, etc.
When flying a terminal area procedure that contains a direct-to-fix (DF; proceed to waypoint XYZ) leg back to the same previous waypoint (generally a 360 turn back), the FMS will remove this DF leg and any corresponding turn direction. As can be seen in the left CDU (control display unit) the procedure should have two MNB waypoints, but as can be seen when the error occurs on the right side, only one MNB is displayed. The FMS will turn to the next waypoint (D099O in this example) which may not be in the direction expected per the procedure.
The FMS software has an anomaly that when the two identical waypoints are inserted and the second is a DF, the FMS removes the second waypoint, the turn bit is lost and the FMS calculates a turn independent of the published procedure.
This will be corrected in a future FMZ6.1 certification load. Honeywell SIL D201011000003 (Rev 10) has been released to document this issue as Item L. It is expected that the database mitigation to pull the affected procedures will be in place starting Cycle 5-2013 (effective 2 May 2013).