Narrative:

The aircraft was in the descent on the creso three arrival into las vegas. The first officer was flying, cleared to 12000 ft. The autoplt was engaged on an inbound radial off of the boulder city VOR. The first officer then initiated a shallow left turn using the autoplt turn knob to make a minor course correction to the left. The flight engineer and I were finishing up the descent checklist passing through approximately 15500 ft. Upon looking at my instruments, I noticed that we were beginning to drift left of the course. I glanced down at the autoplt and noticed that the turn knob was still deflected slightly to the left with the aircraft in a shallow left bank (5 degrees). I directed to first officer to correct back to course by turning right. He did this, and as we were established in the right turn, ZLA controller told us to level at 14000 ft. (Our original clearance had been 12000 ft.) he stated that we had traffic to our left that was climbing out. When the call was received by us to level at 14000 ft, we were at 13900 ft in a shallow descent. The first officer promptly leveled the aircraft at 14000 ft. During the leveloff, the aircraft bottomed out at approximately 13700 ft. My navigation instruments showed approximately 3 degrees left of course at 52 DME from the bld VOR. There were no TCASII alerts or advisories of any kind. We were subsequently cleared to continue the descent and we landed uneventfully. We telephoned ZLA when on the ground and were told by a supervisor that we may have had a lateral course deviation.

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Original NASA ASRS Text

Title: B727 SLIGHTLY OFF COURSE ON ARR TO LAS. ATC LEVELS B727 MOMENTARILY FOR DEPARTING TFC SEPARATION.

Narrative: THE ACFT WAS IN THE DSCNT ON THE CRESO THREE ARR INTO LAS VEGAS. THE FO WAS FLYING, CLRED TO 12000 FT. THE AUTOPLT WAS ENGAGED ON AN INBOUND RADIAL OFF OF THE BOULDER CITY VOR. THE FO THEN INITIATED A SHALLOW L TURN USING THE AUTOPLT TURN KNOB TO MAKE A MINOR COURSE CORRECTION TO THE L. THE FE AND I WERE FINISHING UP THE DSCNT CHKLIST PASSING THROUGH APPROX 15500 FT. UPON LOOKING AT MY INSTS, I NOTICED THAT WE WERE BEGINNING TO DRIFT L OF THE COURSE. I GLANCED DOWN AT THE AUTOPLT AND NOTICED THAT THE TURN KNOB WAS STILL DEFLECTED SLIGHTLY TO THE L WITH THE ACFT IN A SHALLOW L BANK (5 DEGS). I DIRECTED TO FO TO CORRECT BACK TO COURSE BY TURNING R. HE DID THIS, AND AS WE WERE ESTABLISHED IN THE R TURN, ZLA CTLR TOLD US TO LEVEL AT 14000 FT. (OUR ORIGINAL CLRNC HAD BEEN 12000 FT.) HE STATED THAT WE HAD TFC TO OUR L THAT WAS CLBING OUT. WHEN THE CALL WAS RECEIVED BY US TO LEVEL AT 14000 FT, WE WERE AT 13900 FT IN A SHALLOW DSCNT. THE FO PROMPTLY LEVELED THE ACFT AT 14000 FT. DURING THE LEVELOFF, THE ACFT BOTTOMED OUT AT APPROX 13700 FT. MY NAV INSTS SHOWED APPROX 3 DEGS L OF COURSE AT 52 DME FROM THE BLD VOR. THERE WERE NO TCASII ALERTS OR ADVISORIES OF ANY KIND. WE WERE SUBSEQUENTLY CLRED TO CONTINUE THE DSCNT AND WE LANDED UNEVENTFULLY. WE TELEPHONED ZLA WHEN ON THE GND AND WERE TOLD BY A SUPVR THAT WE MAY HAVE HAD A LATERAL COURSE DEV.

Data retrieved from NASA's ASRS site as of July 2007 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.