B757 FMS directs wrong way turn on departure from bos.

Attributes
ACN	435512
Time
Date	199904
Day	Sun
Local Time Of Day	0001 To 0600
Place
Locale Reference	airport : bos.airport
State Reference	MA
Altitude	msl single value : 2000
Environment
Flight Conditions	VMC
Light	Dawn
Aircraft 1
Controlling Facilities	tower : bos.tower
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	climbout : initial
Route In Use	departure sid : wylyy2.bos
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : cfi pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 150
ASRS Report	435512
Person 2
Affiliation	company : air carrier
Function	flight crew : captain
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical non adherence : clearance non adherence : published procedure other anomaly other other spatial deviation
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to original clearance flight crew : returned to intended course
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

Taking off from boston airport to cincinnati. We were departing runway 27 wylly 2 FMS departure. Uneventful takeoff. Engaged FMS in LNAV, started to follow steering on departure climb out. The steering guided me to the right of track. As soon as I realized what was happening, I selected heading select and flew the airplane back to the departure track of the published wylly 2 FMS departure. All else was uneventful, but FMS proved totally wrong for the departure, although the position before takeoff appeared accurately at the end of the runway.

Original NASA ASRS Text

Title: B757 FMS DIRECTS WRONG WAY TURN ON DEP FROM BOS.

Narrative: TAKING OFF FROM BOSTON ARPT TO CINCINNATI. WE WERE DEPARTING RWY 27 WYLLY 2 FMS DEP. UNEVENTFUL TKOF. ENGAGED FMS IN LNAV, STARTED TO FOLLOW STEERING ON DEP CLBOUT. THE STEERING GUIDED ME TO THE R OF TRACK. AS SOON AS I REALIZED WHAT WAS HAPPENING, I SELECTED HDG SELECT AND FLEW THE AIRPLANE BACK TO THE DEP TRACK OF THE PUBLISHED WYLLY 2 FMS DEP. ALL ELSE WAS UNEVENTFUL, BUT FMS PROVED TOTALLY WRONG FOR THE DEP, ALTHOUGH THE POS BEFORE TKOF APPEARED ACCURATELY AT THE END OF THE RWY.

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.