Narrative:

This report is submitted to highlight deficiencies in B737-700 flight instrument display redundancy. During cruise flight; we lost the first officer side airspeed indicator; altimeter and vvi; and they were not recoverable. All other elements of the first officer displays remained normal. Accompanying indications included: momentary airspeed clacker (we were at economy cruise speed); master caution with engine and flight control annunciators; both engines in soft alternate mode; single channel speed trim fail and mach trim fail; first officer side speed and altitude flags; and significant data loss on many pages of both FMC's. The FMC's would not allow altitude inputs for any waypoints. They seemed to have lost all vertical planning capability; but horizontal navigation seemed unaffected. Left side instrumentation and hgs were all normal. We did not have display source flags and both hydraulic pressure gauges were normal. Even with the help of maintenance control via radio; we were unable to recover the first officer instruments. No cockpit circuit breakers were popped. We accomplished QRH procedures for eec alternate lights; but the QRH does not address the rest of this problem. 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 first officer could not properly monitor my approach. Ind was 5000 ft broken; 10 mi visibility. During our radio conversation with maintenance control; they thought we lost the #2 air data computer section of the #2 adiru. The questions unanswered include: 1) why didn't switching the display source deliver good instrument displays to the first officer side? 2) should the QRH address such a partial instrument loss? The unreliable airspeed procedure doesn't fit because the left side displays and hgs were normal. Display source switching had no effect. There are no circuit breakers for the air data computer's; just for the entire adiru's.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of January 2009 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.