2 C172 PLTS HAVE TO OBTAIN VECTORS AND A NO GYROSCOPE APCH AFTER DIVERTING TO ANOTHER ARPT WHEN THEIR DIRECTIONAL GYROSCOPE WAS PRECESSING AT AN ABNORMALLY HIGH RATE WHILE IFR TO 1S0; WA.

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ON A VFR XCOUNTRY FROM 1S0 TO S21. LANDED AT S21 VFR. CHKED THE WX ON THE PHONE. WX FROM PORTLAND AREA N; WAS RPTING MVFR CONDITIONS. FLT INSTRUCTOR AND I ELECTED TO FILE AN IFR FLT PLAN FROM UBG VOR; TO 1S0 WITH ALTERNATE BEING TIW. WE COMPLETED AN IFR TAXI CHKLIST; ALL SYS CHKED OUT CORRECTLY. UPON NEARING THE UBG VOR; WE PICKED UP IFR CLRNC AND CLBED TO 6000 FT MSL. WE ENTERED IMC AT ABOUT 4000 FT MSL BEFORE REACHING UBG; AND WERE IN IMC THE REST OF THE FLT. WE CROSSED UBG AND WENT NBOUND ON V-165. AFTER APPROX 30 MINS OF IMC; WE NOTICED THAT WE HAD TO RESET THE DIRECTIONAL GYROSCOPE TOO OFTEN. IT WAS ALSO PRECESSING ERRATICALLY. IT WOULD HOLD HEADING; THEN PRECESS QUICKLY. AT THIS POINT; WE NOTIFIED ATC OF INOP EQUIP. ATC NOTIFIED US THAT WE HAD ALSO STRAYED FROM THE AIRWAY. WE REQUESTED OUR GND TRACK; AND IT DID NOT SEEM TO MATCH OUR COMPASS HEADING. THE COMPASS WAS ALSO SWINGING TO ALL DIFFERENT HEADINGS; AND WE NOTIFIED ATC OF THIS. FROM HERE OUT; WE RECEIVED NO-GYROSCOPE VECTORS ON V-165; ATC ADVISED US THAT CLOUDS AND VISIBILITY WAS TOO LOW TO GET VECTORED TO IS0 FOR A VISUAL. WE ELECTED TO GET VECTORED FOR AN ILS AT TIW; AND WE VECTORED TO FINAL ON THE LOC AND LANDED SAFELY AT TIW. AFTER FURTHER EVAL WITH MY INSTRUCTOR AND OTHERS; WE FOUND THAT WE WERE SUFFERING FROM 'GET HOMEITIS;' AND THE THING WE SHOULD HAVE DONE; IS TURN AROUND; AND LAND IN SALEM IN VFR. WE WERE FAILING TO SEE THE 'BIG PICTURE' AND LAND WHERE IT WAS NO FACTOR. SUPPLEMENTAL INFO FROM ACN 582688: PASSING THROUGH 4000 FT MSL; WE ENTERED INST CONDITIONS. FROM THIS POINT WE TRACKED TO THE NEWBERG VOR; THEN TURNED N ON V-165 AND TRACKED TO OLM. WE WERE ABOUT 15 NM N OF UBG ON V-165; AND WE WERE NOTICING THAT THE HEADING INDICATOR WAS STARTING TO PRECESS PRETTY RAPIDLY. INSTEAD OF CONTINUING TO FLY A COMPROMISED ACFT INTO WORSE WX AND HAVING TO SHOOT AN INST APCH; THAT THE BEST WX IN THE AREA SHOULD HAVE BEEN OBTAINED; AND WE SHOULD HAVE LANDED AS SOON AS PRACTICAL TO REGROUP. I THINK THAT CONTRIBUTING FACTORS WERE THE RADIO STACK BEING ABNORMALLY HOT; THE INCORRECT FORECAST OF WX; BEING ON AN IFR FLT PLAN (THAT WOULD ONLY GIVE US A 6000 FT MEA); AND 2 PLTS THAT HAD HAD RELATIVELY LITTLE EXPERIENCE WITH A FAILURE OF THIS NATURE WHILE IN IMC. ALSO THE SKILL AND TRAINING OF BOTH PLTS; AND THROUGH GOOD USE OF CRM; WE WERE ABLE TO CTL THE ACFT; AND COMPLETE ALL DUTIES. I WILL ALSO STRESS TO MY INST STUDENTS; THAT A SIT LIKE THIS; ESPECIALLY IF YOU ARE SINGLE PLT; IS AN EMER; AND SHOULD BE HANDLED LIKE ONE (NOT NECESSARILY SQUAWKING 7700 AND SAYING MAYDAY; MAYDAY...BUT SHOULD BE TREATED WITH RESPECT; AND YOU SHOULD FIND THE BEST WX; AND GET DOWN). HAD I HAD THIS MENTALITY; I WOULD HAVE HAD MUCH LESS EXCITING OF A DAY THAT DAY; AND WE WOULD HAVE CONDUCTED THE FLT WITH THE SAFETY THAT WE ALL EXPECT OF OURSELVES AND OUR STUDENTS.