Narrative:

I was pilot monitoring; departure runway 7L at A8 intersection; COWBY2 RNAV SID. All procedures for RNAV departure per fom guidance completed properly and verified. After departure at approximately 2600 ft MSL; LNAV selected on flight director and it began to command a slight right turn. PF began to follow guidance and then the flight director continued to command right turn. Legs page showed waste on L1 and correct track. I stated there was an issue and we should correct back to a 075 degree heading. At that time departure stated we were south of course; however; the CDI showed tracking on course through the entire sequence. ATC gave us direct cowby waypoint; and the waypoint was selected and executed and coupled with flight director and autoplt. Aircraft flew to waypoint; and then approximately 60 seconds later began an uncommanded left turn and continued until LNAV was disengaged by the PF. I requested from ATC we have a heading and to discontinue the RNAV departure due to unknown issues with the flight director. No further incidents occurred during flight. Possibly change master flight director; however; due to the closeness to the course and time restraints; this was unlikely. Supplemental information from acn 779311: the FMC was preflted; verified and re-verified as correct by both the PF and PNF. This was a very strange event and we can only speculate that there was some sort of interference (caused by cell phones/electronic devices; etc). Dispatch; maintenance; and ATC representative notified of event. Stress compliance with use of portable electronic device (ped) regulations.

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Original NASA ASRS Text

Title: B737-300 FLT CREW REPORTS ANOMALOUS COMMANDS FROM FLT DIRECTOR IN LNAV MODE. SUSPECT ELECTRONIC DEVICE INTERFERENCE.

Narrative: I WAS PLT MONITORING; DEP RWY 7L AT A8 INTXN; COWBY2 RNAV SID. ALL PROCS FOR RNAV DEP PER FOM GUIDANCE COMPLETED PROPERLY AND VERIFIED. AFTER DEP AT APPROX 2600 FT MSL; LNAV SELECTED ON FLT DIRECTOR AND IT BEGAN TO COMMAND A SLIGHT R TURN. PF BEGAN TO FOLLOW GUIDANCE AND THEN THE FLT DIRECTOR CONTINUED TO COMMAND R TURN. LEGS PAGE SHOWED WASTE ON L1 AND CORRECT TRACK. I STATED THERE WAS AN ISSUE AND WE SHOULD CORRECT BACK TO A 075 DEG HDG. AT THAT TIME DEP STATED WE WERE S OF COURSE; HOWEVER; THE CDI SHOWED TRACKING ON COURSE THROUGH THE ENTIRE SEQUENCE. ATC GAVE US DIRECT COWBY WAYPOINT; AND THE WAYPOINT WAS SELECTED AND EXECUTED AND COUPLED WITH FLT DIRECTOR AND AUTOPLT. ACFT FLEW TO WAYPOINT; AND THEN APPROX 60 SECONDS LATER BEGAN AN UNCOMMANDED L TURN AND CONTINUED UNTIL LNAV WAS DISENGAGED BY THE PF. I REQUESTED FROM ATC WE HAVE A HDG AND TO DISCONTINUE THE RNAV DEP DUE TO UNKNOWN ISSUES WITH THE FLT DIRECTOR. NO FURTHER INCIDENTS OCCURRED DURING FLT. POSSIBLY CHANGE MASTER FLT DIRECTOR; HOWEVER; DUE TO THE CLOSENESS TO THE COURSE AND TIME RESTRAINTS; THIS WAS UNLIKELY. SUPPLEMENTAL INFO FROM ACN 779311: THE FMC WAS PREFLTED; VERIFIED AND RE-VERIFIED AS CORRECT BY BOTH THE PF AND PNF. THIS WAS A VERY STRANGE EVENT AND WE CAN ONLY SPECULATE THAT THERE WAS SOME SORT OF INTERFERENCE (CAUSED BY CELL PHONES/ELECTRONIC DEVICES; ETC). DISPATCH; MAINT; AND ATC REPRESENTATIVE NOTIFIED OF EVENT. STRESS COMPLIANCE WITH USE OF PORTABLE ELECTRONIC DEVICE (PED) REGS.

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.