Track deviation. - NASA ASRS

Attributes
ACN	298243
Time
Date	199503
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : oak airport : sfo
State Reference	CA
Altitude	msl bound lower : 33000 msl bound upper : 33000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zla
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other ground : preflight
Route In Use	arrival star : star departure other departure sid : sid
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : flight engineer pilot : commercial
Experience	flight time last 90 days : 120 flight time total : 10000 flight time type : 990
ASRS Report	298243
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : less severe non adherence : clearance other spatial deviation
Independent Detector	other controllera
Resolutory Action	other
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Flight from sfo to sna. Programmed offshore 2 SID in FMC system for RNAV routing to svx. Upon receipt of ATC clearance, reprogrammed FMC with porte 9 departure SID to join tandy 2 arrival into sna. (FMC was reprogrammed for this routing due to sfo runway change). For some reason, the FMC routing retained a spurious fix (morro-bay-mqo) in the routing between wages intersection on porte 9 SID and fellows (flw) VOR. Note-mqo is contained on the offshore 2 departure SID. For some reason, the FMC navigation computer database retained this error and smoothly joined wages intersection and fellows VOR. It was a visually logical route, but not the one we were cleared for. ZLA queried our routing and reclred us with no conflict. Both the first officer and myself checked the FMC legs page and route page for proper routing and missed this error in the routing. In essence, the computer software had a glitch and the flight crew didn't catch it.

Original NASA ASRS Text

Title: TRACK DEV.

Narrative: FLT FROM SFO TO SNA. PROGRAMMED OFFSHORE 2 SID IN FMC SYS FOR RNAV RTING TO SVX. UPON RECEIPT OF ATC CLRNC, REPROGRAMMED FMC WITH PORTE 9 DEP SID TO JOIN TANDY 2 ARR INTO SNA. (FMC WAS REPROGRAMMED FOR THIS RTING DUE TO SFO RWY CHANGE). FOR SOME REASON, THE FMC RTING RETAINED A SPURIOUS FIX (MORRO-BAY-MQO) IN THE RTING BTWN WAGES INTXN ON PORTE 9 SID AND FELLOWS (FLW) VOR. NOTE-MQO IS CONTAINED ON THE OFFSHORE 2 DEP SID. FOR SOME REASON, THE FMC NAV COMPUTER DATABASE RETAINED THIS ERROR AND SMOOTHLY JOINED WAGES INTXN AND FELLOWS VOR. IT WAS A VISUALLY LOGICAL RTE, BUT NOT THE ONE WE WERE CLRED FOR. ZLA QUERIED OUR RTING AND RECLRED US WITH NO CONFLICT. BOTH THE FO AND MYSELF CHKED THE FMC LEGS PAGE AND RTE PAGE FOR PROPER RTING AND MISSED THIS ERROR IN THE RTING. IN ESSENCE, THE COMPUTER SOFTWARE HAD A GLITCH AND THE FLC DIDN'T CATCH IT.

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.