IFR FLT IN ICING CONDITIONS COUPLED WITH AN INST FAILURE BROUGHT ON BY A FAILED VACUUM PUMP IN A PA28-181 RESULTS IN A DIVERSION TO AN ENRTE ARPT ON THE WAY TO A CFI INST CHK RIDE.

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I ARRIVED AT HFY (GREENWOOD; IN) FOR A 50 NM TRIP TO MIE (MUNCIE; IN). PURPOSE OF THE TRIP WAS TO MEET DESIGNATED PLT EXAMINER FOR CFI INST PRACTICAL TEST. I CHKED WX USING THE DTN SYS AT THE LCL FBO. WX IN INDIANAPOLIS AREA WAS APPROX 2000 FT BROKEN; 6 SM VISIBILITY; AND IN MUNCIE 900 FT OVCST; 6 SM VISIBILITY. ACFT WAS IN PLACE FOR IFR CONDITIONS AND ICE IN CLOUDS AND PRECIP. I FILED IFR FLT PLAN WITH TERRA HAUTE FSS. PREFLT INSPECTION WAS CARRIED OUT AS WAS PREFLT RUNUP AND CHK OF ALL SYS USING THE CHKLIST. ALL SYS CHKED AND WERE OPERATING NORMAL. THE AIRPLANE WAS PA28-181 PIPER ARCHER II. ONLY DEICE EQUIP IS PITOT HEAT AND CARB HEAT. SOMEWHERE AROUND XA15 I DEPARTED HFY AND AFTER LEAVING THE TFC PATTERN AT HFY; I CONTACTED IND APCH AND PICKED UP MY IFR CLRNC TO MIE. PITOT HEAT WAS ON BEFORE LEAVING THE GND AND WAS OPERATING NORMALLY. AS CLRED; I CLBED TO 3000 FT AND WAS PROCEEDING DIRECT MUNCIE. I NOTED ABOUT 10-15 MINS OUT THAT I WAS PICKING UP LIGHT RIME ICE. AT THAT TIME I TURNED ON CARB HEAT AND RPTED THE LIGHT RIME ICE TO ATC. UPON CLRING IND APCH AIRSPACE I WAS HANDED OFF TO ZID. I THEN NOTED THAT THE RIME ICE ACCUMULATION WAS BECOMING MORE PRONOUNCED. THE TEMP AT 3000 FT WAS ONLY A FEW DEGS BELOW ZERO; SO I KNEW WARMER AIR WAS JUST BELOW. SINCE BY NOW I WAS ONLY ABOUT 10-20 NM OUT FROM MUNCIE; I RPTED THE SIT AND ASKED FOR LOWER ALT. ZID RPTED THE TOPS AT 5500 FT AND OFFERED 6000 FT. I ACCEPTED 6000 FT; BUT MADE UP MY MIND NOT TO CLB THE AIRPLANE AT LESS THAN 100 KIAS SINCE I ALREADY HAD HIGH LIKELIHOOD OF AERODYNAMIC COMPROMISE DUE TO THE ICE. I WANTED TO AVOID POSSIBILITY OF STALL SPIN ACCIDENT. WITH FULL PWR; I CLBED TO 4000 FT AND AT THAT POINT IT BECAME APPARENT THAT THE AIRPLANE WAS NO LONGER CAPABLE OF CLBING AT 100 KIAS OR GREATER DUE TO THE ICE ACCUMULATION AND INCREASED WT AND DECREASED PERFORMANCE. I ADVISED CTR THAT I WANTED TO STAY AT 4000 FT; BUT DID NOT SAY WHY. IT WAS AT THAT TIME THAT I NOTED THE L SIDE VACUUM LOW RED LIGHT ILLUMINATED AND QUICKLY CHKED THE ANNUNCIATOR PANEL LIGHT WHICH WAS ALSO ILLUMINATED AND FURTHER XCHKED THE VACUUM SUCTION GAUGE WHICH READ ZERO. AT THAT TIME I QUICKLY PULLED THE STANDBY VACUUM KNOB WHICH FAILED TO EXTINGUISH THE RED VACUUM LOW LIGHT. THIS BOTHERED ME A GREAT DEAL BECAUSE WHEN GND CHKING THAT SYS AT ENG IDLE THE LIGHT WOULD EXTINGUISH INDICATING PROPER OP OF THE STANDBY VACUUM. AT THIS TIME I BEGAN TO PREPARE TO GO TO PARTIAL PANEL AND WAS FULLY PREPARED TO COVER UP THE ATTITUDE INDICATOR AND HDG INDICATORS TO ELIMINATE THEM FROM THE SCAN. KNOWING THAT NOW WITH 2 SIGNIFICANT PROBS THE SIT COULD BECOME GRAVE WITH ANY MORE FAILURES; I NOTIFIED ATC AND REQUESTED PRIORITY HANDLING. I ADVISED THEM OF THE PROB AND SINCE I WAS JUST XING THE LOC FOR THE ILS RWY 30 AT ANDERSON; WHICH WAS ONLY ABOUT 5 MI AWAY; THEY GAVE ME THE FREQ; TURNED ME ON THE FINAL APCH COURSE; AND CLRED ME FOR THE APCH; WHICH I EXECUTED. I BROKE OUT ABOUT 900 FT AND LANDED WITHOUT INCIDENT. THE ZID SUPVR ASKED ME TO CALL HIM ON GND TELEPHONE TO DISCUSS THE EVENTS; WHICH I DID. THE EVENTUAL MAINT FINDING WAS A BROKEN SHAFT IN THE VACUUM PUMP WHICH CAUSED THE FAILURE. ALSO; LATER FOUND OUT THAT THE RECOMMENDED CHANGE-OUT TIME FOR THE PUMP IS 1000 HRS AND THIS PUMP HAD 1100 HRS ON IT. ZID SUPVR NOTIFIED ME THAT THEY HAD DECLARED AN EMER FOR ME. LESSONS LEARNED: 1) NEVER UNDERESTIMATE THE IMPORTANCE OF ICE -- NO MATTER HOW SHORT THE DISTANCE TO BE TRAVELED. 2) NEXT TIME I WILL CLB DIRECTLY TO 'ON TOP' RATHER THAN WAITING TO SEE HOW MUCH ICE WILL ACCUMULATE; OR IF UNABLE WILL GO BACK TO THE DEP ARPT. 3) NOT DOING #2 ABOVE MEANS YOU ARE ASSUMING THAT ALL OTHER COMPONENTS OF THE AIRPLANE WILL CONTINUE TO FUNCTION NORMALLY. THIS ASSUMPTION COULD GET YOU KILLED BECAUSE MOST OFTEN IT IS THE SNOWBALL EFFECT OF MULTIPLE FACILITIES THAT LEAD TO ACFT ACCIDENTS AND FATALITIES. 4) KNOW WHAT THE RECOMMENDED CHANGE-OUT TIME IS FOR THE VACUUM PUMP AND OTHER COMPONENTS AND COMPLY. 5) KNOW HOW THE 'BACKUP' SYS WORK AND WHAT THE EXPECTED RESPONSE UPON SWITCH TO THEM IS.