Narrative:

I was on the return leg (approximately 1.6 hours) of a non passenger flight that was dispatched to pick up a part for the company that leases the aircraft. I was flying single pilot and ws the only occupant in the aircraft. I was descending on a previous clearance from FL200 to 16000 ft and I had elected to hand fly the aircraft since it was such a smooth and clear day. I had just been given further descent clearance to 11000 ft. I programmed 11000 ft in the altitude alerter and began my descent from 16000 ft. I was making a very shallow descent in an effort to realize as much ground speed as possible from the descent. I was flying wbound into the late afternoon sun. The bright sun shining in the windshield made the cockpit very warm and making me very relaxed. The next thing I remember was being awakened by center calling me on the headsets. I had fallen asleep, when I woke up and took inventory of my situation, I was descending through 10500 ft. That is what center was calling me about. Center then gave me a clearance to 10000 ft. The only good thing about this experience is that all day, the altitude encoder had been giving ATC a reading that was 200 ft higher than the altimeters, which I am sure made my altitude look better to them than it actually was. In the future, I plan to use the autoplt when flying alone, stay more active in the cockpit and maybe have a cup of coffee in hand when flying single pilot. Fatigue has a way of sneaking up on you even on short duty days such as this one.

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Original NASA ASRS Text

Title: A PA31 PLT GOES TO SLEEP DURING DSCNT TO 11000 FT. HE IS AWAKENED BY ARTCC DSNDING THROUGH 10500 FT.

Narrative: I WAS ON THE RETURN LEG (APPROX 1.6 HRS) OF A NON PAX FLT THAT WAS DISPATCHED TO PICK UP A PART FOR THE COMPANY THAT LEASES THE ACFT. I WAS FLYING SINGLE PLT AND WS THE ONLY OCCUPANT IN THE ACFT. I WAS DSNDING ON A PREVIOUS CLRNC FROM FL200 TO 16000 FT AND I HAD ELECTED TO HAND FLY THE ACFT SINCE IT WAS SUCH A SMOOTH AND CLR DAY. I HAD JUST BEEN GIVEN FURTHER DSCNT CLRNC TO 11000 FT. I PROGRAMMED 11000 FT IN THE ALT ALERTER AND BEGAN MY DSCNT FROM 16000 FT. I WAS MAKING A VERY SHALLOW DSCNT IN AN EFFORT TO REALIZE AS MUCH GND SPD AS POSSIBLE FROM THE DSCNT. I WAS FLYING WBOUND INTO THE LATE AFTERNOON SUN. THE BRIGHT SUN SHINING IN THE WINDSHIELD MADE THE COCKPIT VERY WARM AND MAKING ME VERY RELAXED. THE NEXT THING I REMEMBER WAS BEING AWAKENED BY CTR CALLING ME ON THE HEADSETS. I HAD FALLEN ASLEEP, WHEN I WOKE UP AND TOOK INVENTORY OF MY SIT, I WAS DSNDING THROUGH 10500 FT. THAT IS WHAT CTR WAS CALLING ME ABOUT. CTR THEN GAVE ME A CLRNC TO 10000 FT. THE ONLY GOOD THING ABOUT THIS EXPERIENCE IS THAT ALL DAY, THE ALT ENCODER HAD BEEN GIVING ATC A READING THAT WAS 200 FT HIGHER THAN THE ALTIMETERS, WHICH I AM SURE MADE MY ALT LOOK BETTER TO THEM THAN IT ACTUALLY WAS. IN THE FUTURE, I PLAN TO USE THE AUTOPLT WHEN FLYING ALONE, STAY MORE ACTIVE IN THE COCKPIT AND MAYBE HAVE A CUP OF COFFEE IN HAND WHEN FLYING SINGLE PLT. FATIGUE HAS A WAY OF SNEAKING UP ON YOU EVEN ON SHORT DUTY DAYS SUCH AS THIS ONE.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.