PA28 PLT; WITH PAX; LOSES SITUATIONAL AWARENESS ON APCH TO ZZZ; IS ALERTED TO COURSE AND ALTDEV; RECOGNIZING A LOSS OF COCKPIT DISCIPLINE.

Narrative

I WAS FLYING 2 LEGS OF A MEDICAL FLT FROM ZZZ TO ZZZ1 IN THE MORNING; THEN BACK FROM ZZZ1 TO ZZZ EARLY EVENING. SECOND LEG; DEPARTED AT XA30 FROM ZZZ1. ONCE OUT OF CONGESTED CLASS B AIRSPACE; HAD A FINE FLT AT 9000 FT MSL; WHICH PUT US ABOVE MOST LATE AFTERNOON CUMULUS BUILDUPS. LAST 100 NM; CEILINGS 3000-4000 FT AGL. AS WE APCHED ZZZ; WE WERE DSNDED TO 5000 FT; THEN VECTORS FOR ILS RWY 32; DSND TO 3000 FT MSL UNTIL ESTABLISHED. I HAD BEEN TALKING WITH PAX WHILE GENERALLY STAYING AHEAD OF AIRPLANE. AS WE DSNDED THROUGH BROKEN LAYER (BASES RPTED 3200 FT AGL); I MUST HAVE BEEN DISTR; BUT THEN SENSED PLANE ACCELERATING RAPIDLY. WHEN I LOOKED AT ATTITUDE INDICATOR; PLANE WAS 20-30 DEGS NOSE DOWN AND BANKED 45-60 DEGS TO R. I LEVELED AND SLOWED AIRPLANE AND LOOKED AT GPS AND SAW I WAS 90 DEGS TO LOC AND THROUGH THE LOC BY 1/2 MI. TWR ASKED IF I WANTED VECTORS BACK FOR ANOTHER APCH. I SAID NO AND ESTABLISHED 30 DEG INTERCEPT FOR LOC AGAIN. WE HAD BROKEN OUT AND GOT VISUAL CONTACT WITH ARPT AND LANDED WITHOUT INCIDENT. I MADE 2 MAIN MISTAKES: 1) I VIOLATED MY STERILE COCKPIT ON APCH; AND 2) I DIDN'T FOCUS ON THE ATTITUDE INDICATOR WHEN ENTERING THE CLOUDS. I ATTRIBUTE THESE FAILURES OF COCKPIT DISCIPLINE ON A SENSE OF COMPLACENCY AND; TO A CERTAIN EXTENT; FATIGUE. I WAS COMPLACENT IN THINKING THAT THE FLT WAS NEARLY OVER AND WE 'JUST' HAD TO DSND THROUGH A THIN OVCST LAYER BEFORE BREAKING OUT VFR WITH ABOUT A 2000 FT CEILING. FATIGUE MAY HAVE FACTORED IN BECAUSE I HAD SLEPT ONLY A FEW HRS THE NIGHT BEFORE; PLANNING FOR THE INITIAL MORNING FLT AND WARNING ABOUT A MALFUNCTIONING MODE C XPONDER. BY THE TIME WE MADE THE EVENING RETURN ZZZ1 TO ZZZ (ANOTHER 1 HR 45 MIN FLT); IT WAS AFTER XA00 AT DEST. SO FATIGUE MAY HAVE PLAYED A FACTOR. AFTER THESE EVENTS; I RESOLVE TO DO THE FOLLOWING THINGS: 1) I WILL MAINTAIN A STERILE COCKPIT DURING ALL CRITICAL PHASES OF FLT; ESPECIALLY TKOF/DEP AND APCH/LNDG. 2) I WILL FIXATE ON PRIMARY ATTITUDE INSTS WHEN ENTERING CLOUDS AND NOT LET MYSELF BE DISTR BY SECONDARY TASKS.