Narrative:

On right downwind to runway 16L slc at 11000 ft; ATC directed approach would be for runway 16R. Upon inserting runway 16R into the FMC a route discontinuity appeared and upon execution of the ILS approach procedure; the LNAV routing after magne waypoint dropped. The PF and I both looked at the arrival plate and mistakenly saw a 341 degree heading after magne when in fact; we should have proceeded via RNAV from magne to quipa to rroyy and then taken a heading of 341 degrees. The routing was a straight line; but because of a quartering left tailwind; the 341 degree heading let us drift slightly east of the prescribed arrival routing; before turning base; the approach controller reassigned us to runway 16L and we advised the controller that we were on a heading; we should have still been on the RNAV course between quipa and rroyy waypoints. The controller had no further mention; we were in VMC conditions with a B737 in sight on final for runway 16L and were cleared for a subsequent visual to runway 16L with the airport in sight. Approach; landing and rollout were uneventful. I feel that the late runway assignment in unfamiliar terminal airspace led to the route discontinuity and a 'quick glance' of the arrival procedure was misinterped by both the PF and PNF resulting in us flying a heading as opposed to being on the prescribed arrival routing. Supplemental information from acn 765553: on downwind approach switched runways on us. The captain switched runways in the FMC and it dropped out the STAR we were on. We continued on the heading thinking the STAR was almost over and we took a heading the STAR ended with. Approach asked us if we were on a heading and we responded yes. The heading; with the crosswind; blew us across the path the STAR would have been on. During the process I did ask the captain to ask for a heading; but he did think we were close enough to the end of the STAR to be on a heading anyway. We were not.

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Original NASA ASRS Text

Title: B737 FLT CREW REPORTS GOING OFF COURSE ON THE DELTA 1 ARRIVAL TO SLC AFTER A RWY CHANGE THAT CAUSES THE ARRIVAL TO DROP OUT OF THE FMC.

Narrative: ON R DOWNWIND TO RWY 16L SLC AT 11000 FT; ATC DIRECTED APCH WOULD BE FOR RWY 16R. UPON INSERTING RWY 16R INTO THE FMC A RTE DISCONTINUITY APPEARED AND UPON EXECUTION OF THE ILS APCH PROC; THE LNAV ROUTING AFTER MAGNE WAYPOINT DROPPED. THE PF AND I BOTH LOOKED AT THE ARR PLATE AND MISTAKENLY SAW A 341 DEG HDG AFTER MAGNE WHEN IN FACT; WE SHOULD HAVE PROCEEDED VIA RNAV FROM MAGNE TO QUIPA TO RROYY AND THEN TAKEN A HDG OF 341 DEGS. THE ROUTING WAS A STRAIGHT LINE; BUT BECAUSE OF A QUARTERING L TAILWIND; THE 341 DEG HDG LET US DRIFT SLIGHTLY E OF THE PRESCRIBED ARR ROUTING; BEFORE TURNING BASE; THE APCH CTLR REASSIGNED US TO RWY 16L AND WE ADVISED THE CTLR THAT WE WERE ON A HDG; WE SHOULD HAVE STILL BEEN ON THE RNAV COURSE BTWN QUIPA AND RROYY WAYPOINTS. THE CTLR HAD NO FURTHER MENTION; WE WERE IN VMC CONDITIONS WITH A B737 IN SIGHT ON FINAL FOR RWY 16L AND WERE CLRED FOR A SUBSEQUENT VISUAL TO RWY 16L WITH THE ARPT IN SIGHT. APCH; LNDG AND ROLLOUT WERE UNEVENTFUL. I FEEL THAT THE LATE RWY ASSIGNMENT IN UNFAMILIAR TERMINAL AIRSPACE LED TO THE RTE DISCONTINUITY AND A 'QUICK GLANCE' OF THE ARR PROC WAS MISINTERPED BY BOTH THE PF AND PNF RESULTING IN US FLYING A HDG AS OPPOSED TO BEING ON THE PRESCRIBED ARR ROUTING. SUPPLEMENTAL INFO FROM ACN 765553: ON DOWNWIND APCH SWITCHED RWYS ON US. THE CAPT SWITCHED RWYS IN THE FMC AND IT DROPPED OUT THE STAR WE WERE ON. WE CONTINUED ON THE HDG THINKING THE STAR WAS ALMOST OVER AND WE TOOK A HDG THE STAR ENDED WITH. APCH ASKED US IF WE WERE ON A HDG AND WE RESPONDED YES. THE HDG; WITH THE XWIND; BLEW US ACROSS THE PATH THE STAR WOULD HAVE BEEN ON. DURING THE PROCESS I DID ASK THE CAPT TO ASK FOR A HDG; BUT HE DID THINK WE WERE CLOSE ENOUGH TO THE END OF THE STAR TO BE ON A HDG ANYWAY. WE WERE NOT.

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.