Narrative:

We were cleared on the boach departure by clearance delivery at las. Programming of the FMC was normal and route was verified for the departure. FMC update was accomplished taking the active (runway 25R) for departure and the navigation switches were put in the navigation position. Takeoff was normal. At 400 ft; LNAV was selected. Initial steering guidance was a slight right turn. The first officer started to follow the guidance. Realizing the guidance wasn't correct; I selected the legs page; selected rbell to the bottom of the page and back up. I pushed the 'exec' button to give us steering guidance to rbell. The steering guidance gave us a slight left turn which appeared to be correct. On check in with departure; they asked if we were correcting back on course and we advised that we were. At this point we were passing 1000 ft. We selected autoplt and cleaned up the aircraft. The aircraft began a left turn that seemed appropriate for the departure; however; it turned past the heading for roppr which is the next point on the departure. I reselected the legs page and noted that the anp showed an error of approximately 10 NM. Realizing that we couldn't fly the RNAV departure with that error; we advised departure control that we were unable the RNAV departure and requested vectors. They gave us a vector to join the mccarran 3 departure; which we did. Once established on the departure; I rechked the anp on the legs page and it was approximately .3 NM. I rechked it periodically throughout the flight and it stayed within limits. I don't know why we had the anp error we did on departure. The routing for the departure was checked prior to departure and the runway update was accomplished; but there was a significant positional error on departure. In the future; when departing from airports that require an RNAV departure; I will quickly check the anp on the legs page prior to takeoff. Supplemental information from acn 696577: the departure's first fix was rbell; which should have been straight ahead 6.2 NM. I initially hesitated to turn and informed the captain that something was wrong. He reselected rbell on the legs page and executed. I flew the flight director command bars; however; it overshot the first fix. At this point tower asked if we were correcting to get back on course. Looking down; I noticed on the legs page; that the rnp .3/anp 9.7.

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Original NASA ASRS Text

Title: B737-300 FLT CREW HAS A TRACK HDG DEV DURING THE BOACH 2 RNAV DEP FROM RWY 25R LAS.

Narrative: WE WERE CLRED ON THE BOACH DEP BY CLRNC DELIVERY AT LAS. PROGRAMMING OF THE FMC WAS NORMAL AND RTE WAS VERIFIED FOR THE DEP. FMC UPDATE WAS ACCOMPLISHED TAKING THE ACTIVE (RWY 25R) FOR DEP AND THE NAV SWITCHES WERE PUT IN THE NAV POS. TKOF WAS NORMAL. AT 400 FT; LNAV WAS SELECTED. INITIAL STEERING GUIDANCE WAS A SLIGHT R TURN. THE FO STARTED TO FOLLOW THE GUIDANCE. REALIZING THE GUIDANCE WASN'T CORRECT; I SELECTED THE LEGS PAGE; SELECTED RBELL TO THE BOTTOM OF THE PAGE AND BACK UP. I PUSHED THE 'EXEC' BUTTON TO GIVE US STEERING GUIDANCE TO RBELL. THE STEERING GUIDANCE GAVE US A SLIGHT L TURN WHICH APPEARED TO BE CORRECT. ON CHK IN WITH DEP; THEY ASKED IF WE WERE CORRECTING BACK ON COURSE AND WE ADVISED THAT WE WERE. AT THIS POINT WE WERE PASSING 1000 FT. WE SELECTED AUTOPLT AND CLEANED UP THE ACFT. THE ACFT BEGAN A L TURN THAT SEEMED APPROPRIATE FOR THE DEP; HOWEVER; IT TURNED PAST THE HDG FOR ROPPR WHICH IS THE NEXT POINT ON THE DEP. I RESELECTED THE LEGS PAGE AND NOTED THAT THE ANP SHOWED AN ERROR OF APPROX 10 NM. REALIZING THAT WE COULDN'T FLY THE RNAV DEP WITH THAT ERROR; WE ADVISED DEP CTL THAT WE WERE UNABLE THE RNAV DEP AND REQUESTED VECTORS. THEY GAVE US A VECTOR TO JOIN THE MCCARRAN 3 DEP; WHICH WE DID. ONCE ESTABLISHED ON THE DEP; I RECHKED THE ANP ON THE LEGS PAGE AND IT WAS APPROX .3 NM. I RECHKED IT PERIODICALLY THROUGHOUT THE FLT AND IT STAYED WITHIN LIMITS. I DON'T KNOW WHY WE HAD THE ANP ERROR WE DID ON DEP. THE ROUTING FOR THE DEP WAS CHKED PRIOR TO DEP AND THE RWY UPDATE WAS ACCOMPLISHED; BUT THERE WAS A SIGNIFICANT POSITIONAL ERROR ON DEP. IN THE FUTURE; WHEN DEPARTING FROM ARPTS THAT REQUIRE AN RNAV DEP; I WILL QUICKLY CHK THE ANP ON THE LEGS PAGE PRIOR TO TKOF. SUPPLEMENTAL INFO FROM ACN 696577: THE DEP'S FIRST FIX WAS RBELL; WHICH SHOULD HAVE BEEN STRAIGHT AHEAD 6.2 NM. I INITIALLY HESITATED TO TURN AND INFORMED THE CAPT THAT SOMETHING WAS WRONG. HE RESELECTED RBELL ON THE LEGS PAGE AND EXECUTED. I FLEW THE FLT DIRECTOR COMMAND BARS; HOWEVER; IT OVERSHOT THE FIRST FIX. AT THIS POINT TWR ASKED IF WE WERE CORRECTING TO GET BACK ON COURSE. LOOKING DOWN; I NOTICED ON THE LEGS PAGE; THAT THE RNP .3/ANP 9.7.

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.