B737-700 SUFFERS LOSS OF MULTIPLE FO AIR DATA SUPPORTED INST SYS. DIVERTS TO VFR ARPT.

Narrative

THIS RPT IS SUBMITTED TO HIGHLIGHT DEFICIENCIES IN B737-700 FLT INST DISPLAY REDUNDANCY. DURING CRUISE FLT; WE LOST THE FO SIDE AIRSPD INDICATOR; ALTIMETER AND VVI; AND THEY WERE NOT RECOVERABLE. ALL OTHER ELEMENTS OF THE FO DISPLAYS REMAINED NORMAL. ACCOMPANYING INDICATIONS INCLUDED: MOMENTARY AIRSPD CLACKER (WE WERE AT ECONOMY CRUISE SPD); MASTER CAUTION WITH ENG AND FLT CTL ANNUNCIATORS; BOTH ENGS IN SOFT ALTERNATE MODE; SINGLE CHANNEL SPD TRIM FAIL AND MACH TRIM FAIL; FO SIDE SPD AND ALT FLAGS; AND SIGNIFICANT DATA LOSS ON MANY PAGES OF BOTH FMC'S. THE FMC'S WOULD NOT ALLOW ALT INPUTS FOR ANY WAYPOINTS. THEY SEEMED TO HAVE LOST ALL VERT PLANNING CAPABILITY; BUT HORIZ NAV SEEMED UNAFFECTED. L SIDE INSTRUMENTATION AND HGS WERE ALL NORMAL. WE DID NOT HAVE DISPLAY SOURCE FLAGS AND BOTH HYD PRESSURE GAUGES WERE NORMAL. EVEN WITH THE HELP OF MAINT CTL VIA RADIO; WE WERE UNABLE TO RECOVER THE FO INSTS. NO COCKPIT CIRCUIT BREAKERS WERE POPPED. WE ACCOMPLISHED QRH PROCS FOR EEC ALTERNATE LIGHTS; BUT THE QRH DOES NOT ADDRESS THE REST OF THIS PROB. MOVING THE DISPLAY SOURCE SWITCH TO 'BOTH ON 1' DID NOT AFFECT THE DISPLAYS EXCEPT TO BRING UP THE DISPLAY SOURCE AMBER FLAGS ON BOTH SIDES. WE DIVERTED BECAUSE MDW HAD LOW VISIBILITY (4500 FT RVR) AND THE FO COULD NOT PROPERLY MONITOR MY APCH. IND WAS 5000 FT BROKEN; 10 MI VISIBILITY. DURING OUR RADIO CONVERSATION WITH MAINT CTL; THEY THOUGHT WE LOST THE #2 ADC SECTION OF THE #2 ADIRU. THE QUESTIONS UNANSWERED INCLUDE: 1) WHY DIDN'T SWITCHING THE DISPLAY SOURCE DELIVER GOOD INST DISPLAYS TO THE FO SIDE? 2) SHOULD THE QRH ADDRESS SUCH A PARTIAL INST LOSS? THE UNRELIABLE AIRSPD PROC DOESN'T FIT BECAUSE THE L SIDE DISPLAYS AND HGS WERE NORMAL. DISPLAY SOURCE SWITCHING HAD NO EFFECT. THERE ARE NO CIRCUIT BREAKERS FOR THE ADC'S; JUST FOR THE ENTIRE ADIRU'S.