LOSS OF ACFT CONTROL WHEN VACUUM SYSTEM FAILED.

Narrative

ON THE MORNING OF 11/MON/88; I DEPARTED N52 AT APPROX XA42 AM EASTERN STANDARD TIME IN MY SMA. MY DEST WAS CMH. I HAD ADHERED THOROUGHLY TO MY REGULAR PREFLT PROC: A COMPUTER GENERATED WX BRIEFING PERSONAL PREPARATION AND FILING OF AN IFR FLT PLAN; A WX UPDATE WITH CURRENT PIREPS FROM A BRIEFER AT MILLVILLE FSS AN HR PRIOR TO DEP; PREFLT INSPECTION OF THE ACFT INCLUDING WARMING UP THE ENG; THEN SHUTTING DOWN TO TELEPHONE FOR AND RECEIVE A CLRNC. AT THE RELEASE TIME I WAS JUST FINISHING MY PRE-TKOF CHKLIST AND WAS OFF 2 MINS LATER; WELL BEFORE MY VOID TIME. MY INITIAL CLRNC WAS DIRECT SBJ; V30 LANNA; V30 ETX; V12 CTW; DIRECT--CLB AND MAINTAIN 2000' EXPECT 6000' IN 10 SECS; ETC. AFTER DEP I FLEW THIS ROUTING W/O INCIDENT; AS I HAD MANY TIMES BEFORE. THE WX WAS AS FORECAST AND I WAS IN IMC FROM THE POINT WHERE I CLBED THROUGH APPROX 1800'. MY AUTOPLT/FLT DIRECTOR WITH ALT PRESELECT WAS SET PRIOR TO DEP AND DID MOST OF THE FLYING AFTER THE POINT WHERE I PASSED THROUGH 1500'. DURING THE INITIAL STAGES OF THE FLT THE AUTOPLT WAS COUPLED TO THE VOR RECEIVERS AND THEREAFTER TO THE ONI 7000' LORAN RECEIVER. MY ROUTINE WHILE USING THE AUTOPLT IS TO CONTINUALLY MONITOR ALL INSTRUMENTS AND GAUGES. WHILE PASSING OVER THE MOUNTAINS IN PA; I NOTICED THE SLIGHTEST POSSIBLE ACCUMULATION OF RIME ICE. I WOULD DESCRIBE IT AS A DUSTING OF ICE. IT WAS NOT NOTICEABLE ANYWHERE ON THE ACFT (WHICH IS WHITE) EXCEPT ON THE BLACK BOOTS. I ESTIMATE ITS MAX THICKNESS AT 1/32'. IT WAS NOT REALLY AN ACCUMULATION--CERTAINLY NOT ENOUGH TO WARRANT OPERATION OF THE BOOTS. ENRTE THE USUAL FREQ CHANGES OCCURRED. FOR EXAMPLE; ABOUT 1/2-WAY BTWN AGC AND CTW VORTACS I WAS HANDED OFF BY PIT APCH TO CLE CENTER. CLE ADVISED THEY HAD A REVISED CLRNC FOR ME AND I ADVISED 'READY TO COPY.' THE CLRNC WAS 'AFTER PASSING CTW V12 APE DIRECT; MAINTAIN 6000'.' UPON RECEIVING THIS CLRNC I REFERENCED MY LOW ALT CHARTS TO SEE WHAT FREQ CHANGES NEEDED TO BE SET INTO THE ONI 7000 AND THE VOR RECEIVERS. SUDDENLY I NOTICED THE ATTITUDE INDICATOR SHOWED I WAS IN A DIVING LEFT TURN AND THE ALTIMETER INDICATED A RAPID DSCNT. I IMMEDIATELY DECLARED AN EMER; WE ADVISED TO CONTACT PIT APCH; AND HAVING DISCONNECTED THE AUTOPLT; TRIED TO RECOVER CONTROL OF THE ACFT. I WAS UNABLE TO DO THIS UNTIL I PASSED THROUGH APPROX 3000' AND BEGAN TO SEE THE GND INTERMITTENTLY. I COULD SEE I WAS ACTUALLY IN A RIGHT DIVING TURN (PERHAPS A SPIN)! I HAD CONTROL AGAIN AT APPROX 2500'. I CLBED BACK TO 2800' AND REQUESTED VECTORS TO THE NEAREST ARPT. I WAS CLRED AT 3000'; RADAR VECTORS TO WHEELING VOR FOR THE VOR APCH. I REALIZED MY GYROS HAD TUMBLED (EVEN THOUGH THEY NOW APPEARED TO BE WORKING AGAIN) AND I FLEW THIS PART OF THE FLT WITH REF ONLY TO NEEDLE; BALL; AIRSPD; MAGNETIC COMPASS; ALTIMETER AND THE CDI. I NOTICED THE ACFT WAS VERY DIFFICULT TO CONTROL. THERE WERE SWINGS OF THE COMPASS UPT TO +/-30 DEGS AND SWINGS OF ALT UP TO +/-300'. THIS PART OF THE FLT WAS MADE IN IMC; IN AND OUT OF SNOW SHOWERS; WITH INTERMITTENT GND CONTACT UNTIL FINALLY RELIABLE GND CONTACT WAS ESTABLISHED AT 1700' MSL; THE MDA FOR WHEELING (WHOSE ELEVATION IS APPROX 1200' MSL). I TOOK THE ACFT TO ACI AVIATION; AN FBO AT WHEELING; WHOSE DIRECTOR OF MAINT WITH MECH INSPECTED THE ACFT. THEY FOUND THE LEFT VACUUM PUMP HAD FAILED DUE TO A SHAFT BEING SHEARED. THEY SUBSEQUENTLY FOUND POPPED RIVETS AND MAJOR STRESS FOLDS IN THE SHEET METAL ON THE TOP AND NEAR THE ROOT OF EACH WING. THERE WERE ALSO FOUND; ALTHOUGH NOT AS SERIOUS; ON THE HORIZ STABILIZER. I CALLED IN THE PIT GADO AND GAVE A VERBAL RPT OF ALL THIS IN A COUPLE OF PHONE CALLS THAT AFTERNOON. UPON HIS REVIEWING THE MATTER WITH HIS SUPVR; THE MATTER WAS CLASSIFIED AS AN INCIDENT FOR WHICH A WRITTEN RPT WAS TO BE FILED AND FOR WHICH HE PROMISED TO FORWARD APPROPRIATE FORMS. I ALSO MADE VERBAL RPTS TO THE WHEELING TWR MGR AND TO THE SUPVR ON DUTY AT PIT APCH CTL (WHO ADVISED THAT HE HAD MONITORED THE APCH CTLR WITH WHOM I ACTUALLY COMMUNICATED DURING THAT PHASE OF THE INCIDENT). THIS FLT LASTED 2 HRS; 45 MINS. DURING THIS TIME; AMONG OTHER POSSIBLE VIOLATIONS; THERE WERE SEVERAL ALT DEVIATIONS (ONE OF APPROX 4000'). YET; I HAVE NO IDEA WHAT HAPPENED. I DO NOT RECALL AT ANY TIME ENDURING EXCESSIVE G FORCES. I KNOW ONE OF TWO VACUUM PUMPS FAILED. THE OTHER; WHICH SHOULD HAVE RUN THE GYROS BY ITSELF; DID NOT. THE GYROS TUMBLED. AFTER THAT; AT THIS POINT; THE REST IS CONJECTURE. I CANNOT THINK OF ANY RECOMMENDATION I COULD MAKE THAT WOULD HELP AVOID THIS TYPE OF INCIDENT IN THE FUTURE EXCEPT TO FIND OUT WHY THE SECOND VACUUM PUMP DID NOT OPERATE THE GYROS UPON THE FAILURE OF THE FIRST. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: PITOT SYS WAS OPERATING NORMALLY. COULD NOT RECALL THE AIRSPD AT TIME OF BREAKING OUT OF THE CLOUDS AND MAKING THE MANUAL RECOVERY. THIS WAS THE SECOND VACUUM PUMP FAILURE ON THIS ACFT. FBO COULD NOT DETERMINE WHY THE OTHER PUMP DID NOT PICK UP THE LOAD WHEN THE FAILURE OCCURRED. SUSPECT THE SHUTTLE VALVE WAS STICKING FOR SOME REASON. CONSIDERATION WAS GIVEN TO THE POSSIBLE FAILURE OF THE ARTIFICIAL HORIZON AND THIS IS BEING CHKED BY THE MFG. ACFT CAN BE REPAIRED FOR A FERRY FLT; BUT THE INSURANCE PEOPLE ARE STILL DISCUSSING THE REPAIR TO MAKE THE ACFT FULLY AIRWORTHY.