B737 deviates from assigned heading on approach to bos.

Attributes
ACN	418800
Time
Date	199811
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : bos airport : bos
State Reference	MA
Altitude	msl bound lower : 5000 msl bound upper : 5000
Environment
Flight Conditions	Mixed
Light	Night
Aircraft 1
Controlling Facilities	tracon : bos
Operator	common carrier : air carrier
Make Model Name	B737-200
Flight Phase	descent : approach
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	landing other
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 160 flight time total : 16000 flight time type : 5000
ASRS Report	418800
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 180 flight time total : 13000 flight time type : 5000
ASRS Report	418796
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation non adherence : clearance other spatial deviation
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued new clearance flight crew : exited adverse environment other
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 10000 vertical : 500
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

On heading of 210 degrees for downwind leg of runway 4R ILS, controller issued heading of 200 degrees to widen downwind leg. I heard '300 degrees,' and read that back, thinking this was a turn to base leg. After turn, corrective headings were issued immediately before serious traffic conflict occurred. We had visual contact with the traffic on the ILS. Contributing factors: high traffic volume, rapid clrncs being issued, rapid readbacks, in and out of clouds, high workload in cockpit. I discussed the situation with a controller supervisor and he concurred with this report.

Original NASA ASRS Text

Title: B737 DEVIATES FROM ASSIGNED HDG ON APCH TO BOS.

Narrative: ON HDG OF 210 DEGS FOR DOWNWIND LEG OF RWY 4R ILS, CTLR ISSUED HDG OF 200 DEGS TO WIDEN DOWNWIND LEG. I HEARD '300 DEGS,' AND READ THAT BACK, THINKING THIS WAS A TURN TO BASE LEG. AFTER TURN, CORRECTIVE HDGS WERE ISSUED IMMEDIATELY BEFORE SERIOUS TFC CONFLICT OCCURRED. WE HAD VISUAL CONTACT WITH THE TFC ON THE ILS. CONTRIBUTING FACTORS: HIGH TFC VOLUME, RAPID CLRNCS BEING ISSUED, RAPID READBACKS, IN AND OUT OF CLOUDS, HIGH WORKLOAD IN COCKPIT. I DISCUSSED THE SIT WITH A CTLR SUPVR AND HE CONCURRED WITH THIS RPT.

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.