Date: 201303
Local time of day: 1801-2400
Location: DFW.Airport, TX
Flight conditions: VMC
Light: Night
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class B DFW
ATC / advisory: TRACON D10
Aircraft component: FMS/FMC
Component problem: Design
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Distraction; Human-Machine Interface; Time Pressure; Workload
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented; Flight Crew Returned To Clearance; Flight Crew Took Evasive Action; Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: I was pilot not flying. Captain was pilot flying. We were set up and briefed for [Runway] 35C. VMC in between cloud decks. Approaching STONZ on BYP5 Arrival into DFW; ATC issued us [Runway] 35R as landing runway. Captain configured iPad; ILS frequency selection and confirmed minimums. I selected ILS 35R from FMC database. I then 'cleaned up' the legs page and advised Captain that [Runway] 35R was in box. He acknowledged. Approaching STONZ; we were alerted 'Discontinuity' by FMS and quickly realized that we had no waypoint after STONZ. Autopilot was flying airplane straight ahead; not making expected turn to DIRKK. We were soon off course. Captain disengaged autopilot and began left turn back to course. I selected DIRKK as next waypoint and adjusted FMS course to match arrival. We returned to course having deviated by approximately 1 mile. I'm aware of the well-known anomaly in the FMS database that causes the entire arrival to be repeated when selecting a different runway at DFW. I immediately 'cleaned up the legs' when the new runway was entered. BUT; because I selected the same waypoint that I was flying to (the second listing of this waypoint - down the list of waypoints on the arrival) and 'put it on top' of my the current waypoint; the FMS made the update look correctly until the Execute button was pressed. Then it simply reverted to the sequence of waypoints that were already in the box (STONZ; then a discontinuity; then back to LIT and the rest of the fixes). This anomaly is well known - I've seen it before; but I missed it; rushing to get set up. I needed to reverify the legs page after the Execute - poor attention to detail. But please; get that anomaly fixed. It's been several years and this problem still exists.

Callback: The reporter stated that the problem he is experiencing he believes is a design issue which could be addressed by allowing any common waypoint between runways to remain so that track deviations can be minimized.



Synopsis: A B737-800 FMS reverted to the full DFW BYP RNAV arrival beginning at LIT after ATC changed the landing runway to 35R as the aircraft approached STONZ and the crew attempted to change the landing runway.