A B757-200 crew reports erratic track deviations on the ord bradford four (BDF4) arrival.

Attributes
ACN	678162
Time
Date	200511
Local Time Of Day	1201 To 1800
Place
Locale Reference	intersection : benky
State Reference	IL
Altitude	msl single value : 11000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : c90.tracon
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Route In Use	arrival star : bdf
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	678162
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
ASRS Report	678156
Events
Anomaly	non adherence : published procedure non adherence : clearance other anomaly other other spatial deviation
Independent Detector	other controllera
Resolutory Action	controller : issued alert none taken : detected after the fact
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Chart Or Publication Navigational Facility
Primary Problem	Chart Or Publication

Narrative:

En route to benky intersection on bradford four arrival; asked by ATC if we were proceeding to benky intersection. ATC issued vectors and advised we were southeast of the intersection. Right VOR manually tuned to ord VOR 113.9; 062 degree course dial into tuner window. While flying vectors; ord VOR on captain's navigation display shifted to left. This is the third time I've flown this sequence this month and the first time I've experienced a map shift in the B757/B767 aircraft.

Original NASA ASRS Text

Title: A B757-200 CREW RPTS ERRATIC TRACK DEVS ON THE ORD BRADFORD FOUR (BDF4) ARR.

Narrative: ENRTE TO BENKY INTXN ON BRADFORD FOUR ARR; ASKED BY ATC IF WE WERE PROCEEDING TO BENKY INTXN. ATC ISSUED VECTORS AND ADVISED WE WERE SE OF THE INTXN. RIGHT VOR MANUALLY TUNED TO ORD VOR 113.9; 062 DEG COURSE DIAL INTO TUNER WINDOW. WHILE FLYING VECTORS; ORD VOR ON CAPT'S NAV DISPLAY SHIFTED TO LEFT. THIS IS THE THIRD TIME I'VE FLOWN THIS SEQUENCE THIS MONTH AND THE FIRST TIME I'VE EXPERIENCED A MAP SHIFT IN THE B757/B767 ACFT.

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.