Narrative:

Flight departed dal on runway 13R. Climbed runway heading to 6000 ft; told to maintain 6000 ft then right heading 180 degrees with climb to 7000 ft; then right to heading 210 degrees with climb to 10000. Told to proceed direct to jaspa; climb to 17000 ft resume departure. Adjusted heading to jaspa; then selected LNAV and noticed jaspa was colored magenta on B737-700 inboard display unit. Then received clearance to FL230. Approximately 2 to 3 minutes later; ZFW asked if we were on departure routing; then issued an immediate left turn to 140 degrees. At this point; I noticed LNAV was no longer engaged; jaspa was colored white 3 to 4 miles in our 6 O'clock. Aircraft was flying last heading prior to jaspa; but aircraft had not turned south on planned routing. ZFW vectored another aircraft to maintain separation. Prior to re-establishment on departure routing; ZFW cleared us direct centex and cleared us to new frequency. LNAV worked correctly remainder of day. Upon reflection of the event; it's clear LNAV disengaged at some point; unnoticed. It was probably operator error; most likely inadvertent; perhaps a knuckle deselected LNAV while adjusting altitude on MCP?supplemental information from acn 693917: my first time to fly with this first officer; first leg of 4 day trip. Departure control told us to take a heading and then go RNAV direct to jaspa intersection. First officer selected RNAV direct jaspa and continued climb out of 10000 ft. I was talking to jumpseat passenger. Center/departure called us and asked; 'have you joined your departure yet?' I looked at moving map and we had passed jaspa and missed joining our joe pool departure. I responded to center; 'we are correcting to course.' the first officer and I were at a loss to figure out why the autoplt continued past jaspa. I was distracted by the jumpseater conversation and did not see the deviation.

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Original NASA ASRS Text

Title: B737-700 FLT CREW DURING DEP FROM DAL ON THE JOE POOL DEP HAS A HDG/COURSE DEV. DEP CTL VECTORS THE ACFT TO CORRECT COURSE.

Narrative: FLT DEPARTED DAL ON RWY 13R. CLBED RWY HDG TO 6000 FT; TOLD TO MAINTAIN 6000 FT THEN R HDG 180 DEGS WITH CLB TO 7000 FT; THEN R TO HDG 210 DEGS WITH CLB TO 10000. TOLD TO PROCEED DIRECT TO JASPA; CLB TO 17000 FT RESUME DEP. ADJUSTED HDG TO JASPA; THEN SELECTED LNAV AND NOTICED JASPA WAS COLORED MAGENTA ON B737-700 INBOARD DISPLAY UNIT. THEN RECEIVED CLRNC TO FL230. APPROX 2 TO 3 MINUTES LATER; ZFW ASKED IF WE WERE ON DEP ROUTING; THEN ISSUED AN IMMEDIATE L TURN TO 140 DEGS. AT THIS POINT; I NOTICED LNAV WAS NO LONGER ENGAGED; JASPA WAS COLORED WHITE 3 TO 4 MILES IN OUR 6 O'CLOCK. ACFT WAS FLYING LAST HDG PRIOR TO JASPA; BUT ACFT HAD NOT TURNED S ON PLANNED ROUTING. ZFW VECTORED ANOTHER ACFT TO MAINTAIN SEPARATION. PRIOR TO RE-ESTABLISHMENT ON DEP ROUTING; ZFW CLRED US DIRECT CENTEX AND CLRED US TO NEW FREQ. LNAV WORKED CORRECTLY REMAINDER OF DAY. UPON REFLECTION OF THE EVENT; IT'S CLEAR LNAV DISENGAGED AT SOME POINT; UNNOTICED. IT WAS PROBABLY OPERATOR ERROR; MOST LIKELY INADVERTENT; PERHAPS A KNUCKLE DESELECTED LNAV WHILE ADJUSTING ALT ON MCP?SUPPLEMENTAL INFO FROM ACN 693917: MY FIRST TIME TO FLY WITH THIS FO; FIRST LEG OF 4 DAY TRIP. DEP CTL TOLD US TO TAKE A HDG AND THEN GO RNAV DIRECT TO JASPA INTXN. FO SELECTED RNAV DIRECT JASPA AND CONTINUED CLB OUT OF 10000 FT. I WAS TALKING TO JUMPSEAT PAX. CTR/DEP CALLED US AND ASKED; 'HAVE YOU JOINED YOUR DEP YET?' I LOOKED AT MOVING MAP AND WE HAD PASSED JASPA AND MISSED JOINING OUR JOE POOL DEP. I RESPONDED TO CTR; 'WE ARE CORRECTING TO COURSE.' THE FO AND I WERE AT A LOSS TO FIGURE OUT WHY THE AUTOPLT CONTINUED PAST JASPA. I WAS DISTRACTED BY THE JUMPSEATER CONVERSATION AND DID NOT SEE THE DEVIATION.

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.