A B737-300 ON TKOF AT 400 FT THE FLT CTL COMPUTER FAILED AND FLEW BEYOND INITIAL FMC TURN POINT ON SID. CAUSED BY A FAILED FLT CTL COMPUTER.

Narrative

FLT (BOS TO DEN) TKOF FROM RWY 27 AT KBOS; ON A WYLYY THREE DEP. AT 400 FT; THE LNAV WAS SELECTED AS REQUIRED BY THE SID. AT THIS POINT; THE FLT DIRECTOR COUPLING WITH THE FMC FAILED AND I WAS LEFT WITH NO FMC/FD GUIDANCE ON THIS (AN FMS) DEP PROCEDURE. DURING ATTEMPTS TO BRING SYS BACK ONLINE; AND DUE TO HVY PLT WORK LOAD IN FIRST MIN AFTER TKOF; ACFT MAY HAVE FLOWN BEYOND INITIAL FMC TURN POINT ON SID. DME COULD NOT BE CONFIRMED IMMEDIATELY AS AUTO/MANUAL FUNCTION ON NAV RADIO HEAD HAD BEEN SELECTED AS REQUIRED; AND DME DISPLAY HAD BLANKED OUT. PRIORITY WAS ON ACFT CTL AND GAINING ALT. DUE TO NO LATERAL FLT DIRECTOR GUIDANCE AND QUESTIONABLE DME; A QUICK GLANCE OUTSIDE SHOWED THE NOISE SENSITIVE AREA SLIGHTLY LEFT OF CENTER AHEAD. A DECISION TO TURN SLIGHTLY RIGHT WAS MADE FOR THE FOLLOWING REASONS: 1) METROPOLITAN AREA BETTER AVOIDED (BEING COGNIZANT OF CURRENT EVENTS ESPECIALLY); 2) MAP DISPLAY INDICATED A SWEEPING RIGHT TURN WHICH WE WOULD JOIN; 3) LACK OF FMS COUPLED FLT DIRECTOR GUIDANCE TO THE CONTRARY; 4) BEING UNABLE TO DIVERT ATTENTION FROM FLYING TO THE FINE PRINT ON THE SID FOR FURTHER GUIDANCE/INTERPRETATION IN EVENT OF FMC/FD FAILURE. ATC NOTICED OUR PROBLEM; QUERIED HEADING AND GAVE HELPFUL VECTORS TO INCREASE RATE OF INTERCEPTION. REMAINDER OF FLT UNEVENTFUL; FMS/FD FUNCTIONS NORMAL THEREAFTER.