GA SMA DEVIATED FROM PUBLISHED HEADING DURING IAP NDB APCH. WHILE CORRECTING HEADING ALT DEVIATION EXCURSION FROM CLRNC ALT.

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ON EXECUTING 360 DEG VECTOR TO OSM NDB; ACFT COMPASS SYS FAILED AND INDICATED 80-90 DEGS OFF CAUSING TEMPORARY +/-275 DEG HDG WHICH WAS CORRECTED UPON VERIFYING WITH GLARE SHIELD COMPASS. DG WAS SET TO CORRECT HDG AND STAYED ACCURATE FOR DURATION OF FLT. CAUSE UNKNOWN. PLT PERFORMANCE WAS AFFECTED BY THE FOLLOWING: DURING CRUISE NEAR FLM; RIGHT ENG LOST 50% PWR; CORRECTED BY SWITCHING FUEL TANKS. RESULTS: PLT BECAME SOMEWHAT ANXIOUS. COMPASS PROB FURTHERED THE ANXIETY. CTLR TOOK CHARGE AND VECTORED PLT THROUGH THE APCH WITH ADDED QUESTIONS INCLUDING: 'TRNING FLT?' ANSWER; 'NEGATIVE.' 'MODE C READOUT--2700 ASSIGNED 3000?' ALTIMETER SETTING WAS CORRECT AND INDICATED 3000. RADIO SHOP TO CHK SYS. 'WHEN ARE YOU GOING TO BEGIN DSCNT TO MDA?' ANSWERED; 'THAT DSCNT WAS COMMENCING.' PLT BEING ANXIOUS ABOUT RIGHT ENG PERFORMANCE DELAYED DSCNT AS A SAFETY PRECAUTION WHICH WORKED OUT FINE IN LOCATING ARPT. SOLUTION: DUE TO PLT BECOMING ANXIOUS; HE PERMITTED HIS PERFORMANCE TO BECOME LESS THAN SATISFACTORY. THE QUESTION AS TO ALT FURTHERED THE ANXIETY AND PLT CORRECTED BY CLBING 300'. THE CHKOUT OF THE MODE C IS NOT COMPLETE BUT IT IS THE PLT'S FEELING THAT IT WAS CORRECT AS INDICATED AT 3000'. THE COMBINATION OF ENG PWR LOSS; COMPASS PROB AND MODE C FURTHERED PLT'S UNSATISFACTORY PERFORMANCE. ALTHOUGH PLT HAD THE CRAFT UNDER CONTROL AND COMPLETED THE APCH SATISFACTORILY; HE PERMITTED A SERIES OF EVENTS TO SOMEWHAT CONTROL HIM; RATHER THAN THE PLT CTLING HIS REACTIONS. CORRECTIVE ACTION INCLUDED THE FOLLOWING: 1) SHOP TO ANALYZE ENG PWR LOSS; MODE C AND COMPASS SYS. 2) PLT TO IMMEDIATELY TAKE ADDITIONAL TRNING IN 'EMER SITS;' IE; ENG OUT; PARTIAL PANEL; FUEL SYS FAILURE ALONG WITH CONCENTRATED TRNING ON ALL APCHS. SPECIFICALLY NON PRECISION APCHS. 3) INCREASE FREQ OF FLYING TO ASSURE FAMILIARITY OF THE ACFT AND PLT PROFICIENCY.