B737-300 loses FMS map on departure from boston runway 27 when intending to fly the FMS wylyy SID.

Attributes
ACN	472386
Time
Date	200005
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : bos.airport
State Reference	MA
Altitude	msl single value : 1000
Environment
Flight Conditions	Mixed
Weather Elements	Rain
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : a90.tracon tower : bos.tower
Operator	common carrier : air carrier
Make Model Name	B737-500
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	climbout : initial
Route In Use	departure sid : wylyy
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : cfi
Experience	flight time last 90 days : 221 flight time total : 11200 flight time type : 407
ASRS Report	472386
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : instrument pilot : commercial pilot : atp
Events
Anomaly	aircraft equipment problem : critical non adherence : clearance non adherence : published procedure other anomaly other other spatial deviation
Independent Detector	other controllera other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Departing bos airport on scheduled flight to cleveland, we were assigned runway 17 and wylyy 3 FMS SID. FMS programming was crosschecked, departure was briefed. When toga pressed on takeoff, discontinuity occurred with the first 2 fixes of the departure dumped. Rogue electrons? Programming error? Navigation shift? When LNAV was called for at 400 ft AGL, the moving map showed a right circle back to runway. The aforementioned discontinuity. Flight director did not provide any horizontal guidance. Without FMS guidance we turned toward 235 degree heading and tried to revert to raw data approximation of course. Departure control queried our heading. We replied 'turning to 235 degrees.' he (ATC) gave a vector on course. Loss first officer FMS guidance without a backup plan in my mind contributed to these moments of course confusion. There is no published procedure should this happen on this FMS SID. I needed to be more proactive in approximating departure path. My first inclination was to 'check the box' (FMS) rather than fly an approximated lateral navigation path.

Original NASA ASRS Text

Title: B737-300 LOSES FMS MAP ON DEP FROM BOSTON RWY 27 WHEN INTENDING TO FLY THE FMS WYLYY SID.

Narrative: DEPARTING BOS ARPT ON SCHEDULED FLT TO CLEVELAND, WE WERE ASSIGNED RWY 17 AND WYLYY 3 FMS SID. FMS PROGRAMMING WAS XCHKED, DEP WAS BRIEFED. WHEN TOGA PRESSED ON TKOF, DISCONTINUITY OCCURRED WITH THE FIRST 2 FIXES OF THE DEP DUMPED. ROGUE ELECTRONS? PROGRAMMING ERROR? NAV SHIFT? WHEN LNAV WAS CALLED FOR AT 400 FT AGL, THE MOVING MAP SHOWED A R CIRCLE BACK TO RWY. THE AFOREMENTIONED DISCONTINUITY. FLT DIRECTOR DID NOT PROVIDE ANY HORIZ GUIDANCE. WITHOUT FMS GUIDANCE WE TURNED TOWARD 235 DEG HDG AND TRIED TO REVERT TO RAW DATA APPROXIMATION OF COURSE. DEP CTL QUERIED OUR HDG. WE REPLIED 'TURNING TO 235 DEGS.' HE (ATC) GAVE A VECTOR ON COURSE. LOSS FO FMS GUIDANCE WITHOUT A BACKUP PLAN IN MY MIND CONTRIBUTED TO THESE MOMENTS OF COURSE CONFUSION. THERE IS NO PUBLISHED PROC SHOULD THIS HAPPEN ON THIS FMS SID. I NEEDED TO BE MORE PROACTIVE IN APPROXIMATING DEP PATH. MY FIRST INCLINATION WAS TO 'CHK THE BOX' (FMS) RATHER THAN FLY AN APPROXIMATED LATERAL NAV PATH.

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.