B757-200 on bradford arrival to ord experiences track deviation.

Attributes
ACN	676181
Time
Date	200510
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : ord.airport
State Reference	IL
Altitude	msl single value : 16000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau.artcc
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Navigation In Use	other Other
Flight Phase	descent : intermediate altitude
Route In Use	arrival star : bradford 4
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	676181
Person 2
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : critical non adherence : published procedure non adherence : clearance other spatial deviation
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued advisory flight crew : overrode automation flight crew : returned to intended or assigned course flight crew : overcame equipment problem
Consequence	other
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance Navigational Facility
Primary Problem	Aircraft

Narrative:

While flying the bradford 4 approach; en route to the benke intersection; the FMC displayed the aircraft symbol on the HSI as on the magenta line. However; instead of the magenta line bisecting the triangle or the triangle being slightly off center; but parallel to the magenta line; the aircraft symbol was biased 60 degrees off; even though the tip of the triangle was touching the magenta line. ZAU asked what our heading was and asked if we were proceeding towards jot and not benke. He then stated that this frequently happened after a new approach was in our type aircraft's database. He then gave us instructions to proceed directly to ord and we then used raw data for the remainder of the approach. Maintenance indicated it might be a corrupted database that was loaded into the FMC.

Original NASA ASRS Text

Title: B757-200 ON BRADFORD ARR TO ORD EXPERIENCES TRACK DEV.

Narrative: WHILE FLYING THE BRADFORD 4 APCH; ENRTE TO THE BENKE INTXN; THE FMC DISPLAYED THE ACFT SYMBOL ON THE HSI AS ON THE MAGENTA LINE. HOWEVER; INSTEAD OF THE MAGENTA LINE BISECTING THE TRIANGLE OR THE TRIANGLE BEING SLIGHTLY OFF CTR; BUT PARALLEL TO THE MAGENTA LINE; THE ACFT SYMBOL WAS BIASED 60 DEGS OFF; EVEN THOUGH THE TIP OF THE TRIANGLE WAS TOUCHING THE MAGENTA LINE. ZAU ASKED WHAT OUR HDG WAS AND ASKED IF WE WERE PROCEEDING TOWARDS JOT AND NOT BENKE. HE THEN STATED THAT THIS FREQUENTLY HAPPENED AFTER A NEW APCH WAS IN OUR TYPE ACFT'S DATABASE. HE THEN GAVE US INSTRUCTIONS TO PROCEED DIRECTLY TO ORD AND WE THEN USED RAW DATA FOR THE REMAINDER OF THE APCH. MAINT INDICATED IT MIGHT BE A CORRUPTED DATABASE THAT WAS LOADED INTO THE FMC.

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.