A PA46T PILOT EXECUTED A MISSED APPROACH AFTER A LOW VISIBILITY APPROACH BUT FAILED TO REENGAGE AUTOPLT. THE AIRCRAFT DID NOT LEVEL AT THE ASSIGNED ALTITUDE AND FLEW THROUGH THE ASSIGNED HEADING. FATIGUE WAS A FACTOR.

Narrative

IT WAS THE END OF A LONG DAY OF FLYING FOR ME; AND I WAS SINGLE PLT. COMING INTO MY DEST I KNEW I WOULD HAVE TO EXECUTE A NIGHTTIME APCH IN 'HARD IFR.' THE APCH WENT WELL; BUT AT THE BOTTOM (MDA) OF THIS NON-PRECISION LOC ONLY; I HAD TO MISS; I RPTED TO TWR THAT I WAS MISSED APCH AND FLYING THE PUBLISHED MISS. TWR HANDED ME OVER TO APCH AGAIN. DURING THE MISS I USED THE 'GAR' FEATURE ON THE FLT DIRECTOR (WHICH DISCONNECTS THE AUTOPLT) AND BEGAN HAND FLYING THE MISS. SEQUENCING THE GPS; AND PROGRAMMING THE AUTOPLT TO FLY THE MISS; I REENGAGED; (OR SO I THOUGHT); THE AUTOPLT. I FAILED TO OBSERVE THAT THE AUTOPLT DID NOT ACTUALLY ENGAGE (THE ANNUNCIATOR IS NOT BRIGHTLY LIT; AND I MUST NOT HAVE HIT THE BUTTON FIRMLY ENOUGH). THE AIR WAS FAIRLY SMOOTH AND THE AIRPLANE WAS IN THE CLBING TURN; AND STEADY; AS I EXPECTED IT TO BE. BUT ACTUALLY 'NO-ONE' WAS FLYING THE AIRPLANE FOR SEVERAL SECONDS. I LOOKED DOWN TO AGAIN; REVIEW THE PROC; AND WHEN I LOOKED UP; THE AIRPLANE WAS STILL IN THE SLIGHT L TURN PAST THE DESIRED HDG; AND ABOVE THE DESIRED MISSED APCH ALT OF 2000 FT; BY SEVERAL HUNDRED FEET. WITHIN SECONDS THE APCH CTLR ASKED (NICELY) IF THE TWR HAD GIVEN DIFFERENT MISSED APCH PROCS TO FLY; OR WOULD I FLY THE PUBLISHED MISSED; TO WHICH I REPLIED; I WOULD FLY THE PUBLISHED MISS. HE THEN ADVISED TO 'FLY THE PUBLISHED MISS; AND MAINTAIN 2000.' SINCE I WAS NEARING 2900 FT; I IMMEDIATELY BEGAN A DSCNT TO ALT AND BACK ON COURSE; BY HAND FLYING; THEN REENGAGED THE AUTOPLT; CONFIRMING ITS OP! THERE WAS NOTHING ELSE SAID FROM ATC OTHER THAN THE NORMAL COM FOR THE APCH CLRNC. THE SECOND APCH WAS ALSO GOOD AND RESULTED IN AN UNEVENTFUL LNDG. THE POINT IS; THAT AUTOMATION IS GOOD; BUT MUST BE MONITORED CAREFULLY; EVEN IF WE ARE VERY FAMILIAR WITH IT (AS I AM WITH THIS GLASS PANELED MERIDIAN). MORE IMPORTANTLY; AS WAS THE CASE FOR ME HERE; WHEN WE HAVE HAD A LONG DAY; WE MUST BE EVEN MORE DILIGENT IN MONITORING OURSELVES FOR FATIGUE; AND DOUBLE (OR EVEN TRIPLE) CHK AGAINST OURSELVES; FOR SMALL OR LARGE ERRORS. I FLY SINGLE PLT MOST OF THE TIME FOR MY COMPANY; AND I KNOW THIS; YET WAS STILL VULNERABLE. I'M SO GLAD NOTHING SERIOUS HAPPENED DUE TO THIS.