Narrative:

On climb out from cleveland after getting radar vectors northwest of the airport; ATC issued a clearance direct to djb. As PF; I line selected djb to the top of the legs page; hit execute; and hit LNAV. I checked that LNAV engaged; and we proceeded to djb. After a few mins we were handed off to ZOB. A few mins later center asked us if we were proceeding to fdy. We looked down at the FMC and saw that we were flying a 'radar vector' segment on the legs page. We replied that we were flying a vector. Center responded with a direct clearance to fdy. I entered fdy at the top of the legs page and we proceeded toward fdy. We don't know how a radar vector segment entered our flight plan on the legs page; as it was not there on initial programming; and it was not possible to enter one manually. The autoplt never left LNAV mode after my initial execution. It seemed like some kind of FMS error; but we couldn't figure out how it would happen. I don't know how I could have mis-programmed the FMC this way; as there was no way to insert a radar vector into the legs; nor was there a radar vector segment anywhere in the original SID. Perhaps there is a software glitch. Callback conversation with reporter acn #809542 revealed the following information: this reporter is positive that the OBRLN1 departure was correctly loaded along with the correct transition. There were no route discontinuities and the legs page did not have a vector segment. After crossing djb; they were queried by ATC; which was the first indication of a problem.

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Original NASA ASRS Text

Title: B737 FLIGHT CREW REPORTS GOING OFF COURSE ON THE OBRLN1 DEPARTURE FROM CLE AFTER PASSING DJB FOR UNKNOWN REASONS.

Narrative: ON CLBOUT FROM CLEVELAND AFTER GETTING RADAR VECTORS NW OF THE ARPT; ATC ISSUED A CLRNC DIRECT TO DJB. AS PF; I LINE SELECTED DJB TO THE TOP OF THE LEGS PAGE; HIT EXECUTE; AND HIT LNAV. I CHKED THAT LNAV ENGAGED; AND WE PROCEEDED TO DJB. AFTER A FEW MINS WE WERE HANDED OFF TO ZOB. A FEW MINS LATER CTR ASKED US IF WE WERE PROCEEDING TO FDY. WE LOOKED DOWN AT THE FMC AND SAW THAT WE WERE FLYING A 'RADAR VECTOR' SEGMENT ON THE LEGS PAGE. WE REPLIED THAT WE WERE FLYING A VECTOR. CTR RESPONDED WITH A DIRECT CLRNC TO FDY. I ENTERED FDY AT THE TOP OF THE LEGS PAGE AND WE PROCEEDED TOWARD FDY. WE DON'T KNOW HOW A RADAR VECTOR SEGMENT ENTERED OUR FLT PLAN ON THE LEGS PAGE; AS IT WAS NOT THERE ON INITIAL PROGRAMMING; AND IT WAS NOT POSSIBLE TO ENTER ONE MANUALLY. THE AUTOPLT NEVER LEFT LNAV MODE AFTER MY INITIAL EXECUTION. IT SEEMED LIKE SOME KIND OF FMS ERROR; BUT WE COULDN'T FIGURE OUT HOW IT WOULD HAPPEN. I DON'T KNOW HOW I COULD HAVE MIS-PROGRAMMED THE FMC THIS WAY; AS THERE WAS NO WAY TO INSERT A RADAR VECTOR INTO THE LEGS; NOR WAS THERE A RADAR VECTOR SEGMENT ANYWHERE IN THE ORIGINAL SID. PERHAPS THERE IS A SOFTWARE GLITCH. CALLBACK CONVERSATION WITH RPTR ACN #809542 REVEALED THE FOLLOWING INFO: THIS RPTR IS POSITIVE THAT THE OBRLN1 DEP WAS CORRECTLY LOADED ALONG WITH THE CORRECT TRANSITION. THERE WERE NO RTE DISCONTINUITIES AND THE LEGS PAGE DID NOT HAVE A VECTOR SEGMENT. AFTER XING DJB; THEY WERE QUERIED BY ATC; WHICH WAS THE FIRST INDICATION OF A PROB.

Data retrieved from NASA's ASRS site as of May 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.