Narrative:

Immediately upon crossing orf, our aircraft made a steep turn to the left in an attempt to go back to our previous chkpoint. I manually stopped the turn using heading select, which disconnects lateral navigation mode of the FMS, and turned right, back on course. The error was caught quickly, but we still went left of course somewhat. I reported this fact to ZDC. Reprogramming FMS route solved the navigation problem. Much searching solved where the problem originated. On our flight plan, when the FMS route is not entered in the same 'wording' as an ATC clearance, it was discovered that the route was entered in error (on both the flight crew plan and therefore in the aircraft's FMS). Dispatch was contacted and also saw the error so it hopefully is fixed in the company's computer system. Our normal preflight FMS route check makes it difficult to spot this error (we entered it to check!) to be sure it is there but somewhat subtle. Omega navigation aircraft illuminate an 'alert' light just before navigation fix passage, alerting the crew to check to see that the next fix is indeed the desired one. After this occurrence, I would enthusiastically endorse an alert function on FMS equipped aircraft. Supplemental information from acn 252420: also, recommend that 180 degree course reversals be clearly indicated on the map display. Currently, the FMC places one course line on top of another, creating a slightly brighter line not easily distinguished from the normal line. Supplemental information from acn 252506: error was corrected for future flight plans.

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Original NASA ASRS Text

Title: AN ACR LGT WITH ALL OF THE LATEST NAV AND INSTRUMENTATION ATTEMPTED TO REVERSE COURSE.

Narrative: IMMEDIATELY UPON XING ORF, OUR ACFT MADE A STEEP TURN TO THE L IN AN ATTEMPT TO GO BACK TO OUR PREVIOUS CHKPOINT. I MANUALLY STOPPED THE TURN USING HDG SELECT, WHICH DISCONNECTS LATERAL NAV MODE OF THE FMS, AND TURNED R, BACK ON COURSE. THE ERROR WAS CAUGHT QUICKLY, BUT WE STILL WENT L OF COURSE SOMEWHAT. I RPTED THIS FACT TO ZDC. REPROGRAMMING FMS RTE SOLVED THE NAV PROB. MUCH SEARCHING SOLVED WHERE THE PROB ORIGINATED. ON OUR FLT PLAN, WHEN THE FMS RTE IS NOT ENTERED IN THE SAME 'WORDING' AS AN ATC CLRNC, IT WAS DISCOVERED THAT THE RTE WAS ENTERED IN ERROR (ON BOTH THE FLC PLAN AND THEREFORE IN THE ACFT'S FMS). DISPATCH WAS CONTACTED AND ALSO SAW THE ERROR SO IT HOPEFULLY IS FIXED IN THE COMPANY'S COMPUTER SYS. OUR NORMAL PREFLT FMS RTE CHK MAKES IT DIFFICULT TO SPOT THIS ERROR (WE ENTERED IT TO CHK!) TO BE SURE IT IS THERE BUT SOMEWHAT SUBTLE. OMEGA NAV ACFT ILLUMINATE AN 'ALERT' LIGHT JUST BEFORE NAV FIX PASSAGE, ALERTING THE CREW TO CHK TO SEE THAT THE NEXT FIX IS INDEED THE DESIRED ONE. AFTER THIS OCCURRENCE, I WOULD ENTHUSIASTICALLY ENDORSE AN ALERT FUNCTION ON FMS EQUIPPED ACFT. SUPPLEMENTAL INFORMATION FROM ACN 252420: ALSO, RECOMMEND THAT 180 DEG COURSE REVERSALS BE CLRLY INDICATED ON THE MAP DISPLAY. CURRENTLY, THE FMC PLACES ONE COURSE LINE ON TOP OF ANOTHER, CREATING A SLIGHTLY BRIGHTER LINE NOT EASILY DISTINGUISHED FROM THE NORMAL LINE. SUPPLEMENTAL INFORMATION FROM ACN 252506: ERROR WAS CORRECTED FOR FUTURE FLT PLANS.

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.