Narrative:

During cruise flight in navigation mode to mlp and between MLS and msp; an mcdu message appeared; 'confirm update at MLS.' as the captain and I looked puzzled at each other; he went to clear the message; but instead the message was confirmed when he pressed the mcdu key. There was an immediate map shift; so the captain pulled for heading mode to maintain present course. The map then showed us about 15 mi north of our navigation course and overflying MLS. We notified ATC of a possible position error and reconfirmed our heading was taking us to mlp. The captain and I consulted our flight manuals; saw how the message should have been cleared; and how to again update to a known position. We tuned the lwt VOR; which was directly ahead and on our course for raw data and requested from ATC direct to lwt then direct mlp. ATC did not question the request. Using raw data; we overflew lwt and updated our position on the progress page to reset the map. We continued to mlp and yvr without incident; confident of our updated correct position; but with continuous raw data xchks along the route and in the terminal area. We were VFR during the entire incident and cleared for a visual approach upon our arrival to yvr. I believe this particular mcdu message should be highlighted to crews during training; as it can innocently result in a self-induced gross navigation error.

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Original NASA ASRS Text

Title: AN A319 MCDU DISPLAYED 'CONFIRM UPDATE AT ZZZ.' ACCIDENTAL ACTIVATION OF THAT SELECTION CAUSED A MAP SHIFT THAT WAS CORRECTED WITH ANOTHER UPDATE.

Narrative: DURING CRUISE FLT IN NAV MODE TO MLP AND BTWN MLS AND MSP; AN MCDU MESSAGE APPEARED; 'CONFIRM UPDATE AT MLS.' AS THE CAPT AND I LOOKED PUZZLED AT EACH OTHER; HE WENT TO CLR THE MESSAGE; BUT INSTEAD THE MESSAGE WAS CONFIRMED WHEN HE PRESSED THE MCDU KEY. THERE WAS AN IMMEDIATE MAP SHIFT; SO THE CAPT PULLED FOR HDG MODE TO MAINTAIN PRESENT COURSE. THE MAP THEN SHOWED US ABOUT 15 MI N OF OUR NAV COURSE AND OVERFLYING MLS. WE NOTIFIED ATC OF A POSSIBLE POS ERROR AND RECONFIRMED OUR HDG WAS TAKING US TO MLP. THE CAPT AND I CONSULTED OUR FLT MANUALS; SAW HOW THE MESSAGE SHOULD HAVE BEEN CLRED; AND HOW TO AGAIN UPDATE TO A KNOWN POS. WE TUNED THE LWT VOR; WHICH WAS DIRECTLY AHEAD AND ON OUR COURSE FOR RAW DATA AND REQUESTED FROM ATC DIRECT TO LWT THEN DIRECT MLP. ATC DID NOT QUESTION THE REQUEST. USING RAW DATA; WE OVERFLEW LWT AND UPDATED OUR POS ON THE PROGRESS PAGE TO RESET THE MAP. WE CONTINUED TO MLP AND YVR WITHOUT INCIDENT; CONFIDENT OF OUR UPDATED CORRECT POS; BUT WITH CONTINUOUS RAW DATA XCHKS ALONG THE RTE AND IN THE TERMINAL AREA. WE WERE VFR DURING THE ENTIRE INCIDENT AND CLRED FOR A VISUAL APCH UPON OUR ARR TO YVR. I BELIEVE THIS PARTICULAR MCDU MESSAGE SHOULD BE HIGHLIGHTED TO CREWS DURING TRAINING; AS IT CAN INNOCENTLY RESULT IN A SELF-INDUCED GROSS NAV ERROR.

Data retrieved from NASA's ASRS site as of January 2009 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.