Date: 201404
Local time of day: 0601-1200
Location: DAL.Airport, TX
Flight conditions: IMC
Weather elements / visibility: 7
Light: Daylight
Aircraft: Commercial Fixed Wing
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; Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Human factors: Confusion; Human-Machine Interface; Troubleshooting; Workload; Distraction
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Aircraft Automation Overrode Flight Crew; Flight Crew Became Reoriented; Flight Crew Took Evasive Action; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Aircraft; Equipment / Tooling; Procedure
Primary problem: Ambiguous

Narrative: We planned an ILS-Y to [Runway] 13R into DAL. We were asked which runway we preferred and agreed to stick with our plan. Approaching FUZ on the arrival; ATC then said cleared the ILS-Z to [Runway] 13R; cross HURBS at/above 4;000 FT. First Officer (pilot flying) was changing out his approach charts while I (pilot not flying) had the ILS page ready and then selected the ILS-Z 13R on the CDU. When First Officer was ready; I asked if he was good with the selection; he said yes; and then I executed it. At that point we were in a turn to HURBS; and got a route discontinuity. As I wasn't positive we had passed FUZ yet; I wasn't comfortable selecting HURBS to the top and executing. So we asked for a vector and received one pretty quick; but I'm sure we overturned the turn to HURBS because by the time we got the vector; we were in CWS roll and not sure what heading to roll out on. I need to be 100% sure of the next go-to waypoint before executing a runway or approach change; so if this happens; we can correct immediately. It might also be helpful in DAL if they publish the ATIS saying expect ILS-Z to 13R and ILS-Y to 13L; or whatever the case is; so we can program much further out. But I need to execute more accurately. Changed to ILS-Z to 13R during descent near FUZ/got route discontinuity and asked for vector.

Callback: The reporter stated that both pilots viewed and confirmed the approach selection to ILS-Z 13R before it was executed. The events following the EXEC selection were very confusing and the reporter does not recall exactly what the FMS displayed other than a route discontinuity because he was busy trying to figure out what the airplane was doing. He did positively see the FMS transition to CWS ROLL and the pitch control remain in LVL CHG. The reporter is frustrated because making an approach and runway change should be a simple process.

Second narrative: We were on arrival into DAL and set up for the ILS Y 13R as that was the Captain's approach expectation based on his experience. Autopilot was engaged in LNAV and LVL CHG at 210 KTS with spoilers deployed. Approaching FUZ on the arrival; we were switched to DAL Approach and subsequently assigned the ILS Z 13R transition via HURBS. As the aircraft was in the turn to HURBS over the FUZ VOR; the Captain changed the approach in the FMC and for some reason the whole arrival reinserted itself; leaving us with a discontinuity as the 'TO' point. As a result; the Flight Director disappeared and the aircraft remained in its current bank. We recognized this quickly; but not before we'd turned about 50 degrees past the course heading. We immediately notified ATC and requested a vector to HURBS. We ended up just receiving vectors to the ILS 13R and completed the approach and landing uneventfully. I later asked the Captain if he had reselected the Arrival when changing the approach and he said he had not. I did not confirm his selections in the FMC before the changes were executed; so I cannot verify what the inputs were. Therefore; I do not know why the entire arrival reinserted itself.Establish clear; concise procedures for verifying FMC and MCP inputs. I also think it's probably a good technique to load the approach that includes the transition because switching to vectors is less complicated than switching to a transition. Plus; having an approach transition loaded provides the most accurate information regarding the progress of your descent (high or low).


Synopsis: An air carrier crew expected the ILS-Y 13R and programmed the FMS as such but after ATC assigned ILS-Z 13R over FUZ the FMS was reprogrammed and when EXECUTE was selected the FMS reinserted the entire arrival; the autopilot transitioned to CWS and the flight director command bars biased out of view. The aircraft turn about 50 degrees beyond a heading to HURBS from over FUZ.