Narrative:

Descending on the canuk 7 RNAV arrival; runway 8L transition approaching doevr intersection at 12;000 ft and 250 KTS; as assigned by atl approach controller. With approximately 1 minute remaining to doevr; the approach controller asks if we are on the canuk 7 RNAV arrival. I checked the navigation display and FMC legs page and both indicate doevr as the active waypoint. I also confirm the balance of the waypoints on the arrival and note the only discontinuity at wotba where the arrival terminates in a 272 degree heading. While responding to approach control that we were in fact on the canuk 7; both FMC reset amber lights illuminated; LNAV disconnected; and the aircraft proceeded on its last track failing to turn left to 272 degrees and toward the nofiv intersection. The reason for the FMC reset was an apparent route discontinuity that appeared at the moment we crossed doevr. While explaining the nature of the navigation system failure; we were assigned a left turn heading to avoid traffic arriving from the north and to rejoin the arrival. We received second and immediate left turn to maintain separation with the aforementioned traffic now reported at approximately 2 o'clock and 3 miles. As I reported the traffic in sight and was asked to maintain visual separation; the captain disconnected the autopilot and immediately turned to the new assigned heading. I worked to correct the discontinuity on the FMC legs page as the captain complied with ATC instructions. After cleaning up the legs page and executing an intercept leg into nofiv; I advised ATC that we could rejoin the arrival at any time. The approach controller cleared us to rejoin as requested and we subsequently received vectors from the final approach controller for an uneventful visual approach and landing. After a postflight discussion; neither of us could discern the reason for the FMC reset or 'pop-up' discontinuity as all indications appeared normal up to the point of the FMC reset and subsequent deviation from the arrival. While it must have been apparent to the controller that we would overshoot doevr; there were no such indications on the flight deck as doevr remained active on the legs page and navigation display until the reset occurred. It proved difficult to prepare for or recognize the potential for such a system failure. Since trapping the error was difficult then mitigating its effects became our priority. By rapidly and aggressively intervening to return the aircraft to the arrival course we prevented a loss of separation with another aircraft. Additionally; if the controller had been more specific in his initial query we may have been better prepared to prevent or respond to the ensuing failure.

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Original NASA ASRS Text

Title: A B737-NG experienced a dual FMC reset on the ATL CANUK 7 RNAV arrival because of a route discontinuity that was not obvious to the flight crew. All FMC and ND indications were normal up to the point of the reset.

Narrative: Descending on the CANUK 7 RNAV arrival; Runway 8L transition approaching DOEVR Intersection at 12;000 FT and 250 KTS; as assigned by ATL Approach Controller. With approximately 1 minute remaining to DOEVR; the Approach Controller asks if we are on the CANUK 7 RNAV Arrival. I checked the Navigation Display and FMC legs page and both indicate DOEVR as the active waypoint. I also confirm the balance of the waypoints on the arrival and note the only discontinuity at WOTBA where the arrival terminates in a 272 degree heading. While responding to Approach Control that we were in fact on the CANUK 7; both FMC reset amber lights illuminated; LNAV disconnected; and the aircraft proceeded on its last track failing to turn left to 272 degrees and toward the NOFIV Intersection. The reason for the FMC reset was an apparent route discontinuity that appeared at the moment we crossed DOEVR. While explaining the nature of the navigation system failure; we were assigned a left turn heading to avoid traffic arriving from the north and to rejoin the arrival. We received second and immediate left turn to maintain separation with the aforementioned traffic now reported at approximately 2 o'clock and 3 miles. As I reported the traffic in sight and was asked to maintain visual separation; the Captain disconnected the autopilot and immediately turned to the new assigned heading. I worked to correct the discontinuity on the FMC legs page as the Captain complied with ATC instructions. After cleaning up the legs page and executing an intercept leg into NOFIV; I advised ATC that we could rejoin the arrival at any time. The Approach Controller cleared us to rejoin as requested and we subsequently received vectors from the Final Approach Controller for an uneventful visual approach and landing. After a postflight discussion; neither of us could discern the reason for the FMC reset or 'pop-up' discontinuity as all indications appeared normal up to the point of the FMC reset and subsequent deviation from the arrival. While it must have been apparent to the Controller that we would overshoot DOEVR; there were no such indications on the flight deck as DOEVR remained active on the legs page and Navigation Display until the reset occurred. It proved difficult to prepare for or recognize the potential for such a system failure. Since trapping the error was difficult then mitigating its effects became our priority. By rapidly and aggressively intervening to return the aircraft to the arrival course we prevented a loss of separation with another aircraft. Additionally; if the Controller had been more specific in his initial query we may have been better prepared to prevent or respond to the ensuing failure.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.