Narrative:

During climb out of fwa, I was showing an area of thunderstorms and developing thunderstorms just to the north of my intended course. I was level at 3000' when I asked fwa departure for a deviation to the south. The deviation was approved and I was instructed to climb and maintain 4000'. The autoplt was engaged and I set it to level off at 4000'. I was very busy at this point, operating the radar and studying the en route chart for a new route of flight and destination. At 3800', I trimmed the autoplt for about a 200 FPM climb. I continued working with the radar and en route chart. A few mins later, fwa advised me that my mode C indicated 4500' and asked if I wanted 5000' as a final altitude. I said that 4000' would be fine and apologized for the altitude deviation. Some factors which I believe contributed to this incident were: 1) lack of a second pilot/reliance on the autoplt. 2) the area of thunderstorms/turbulence which I was deviating around. 3) the importance of the air ambulance flight which led me to flying near an area of severe thunderstorms. 4) this was my second charter flight of the day and I had been on duty over 9 hours at the time of the incident. I don't know what can be done to prevent altitude deviations in the future. They seem to happen in all aircraft regardless of the # of pilots aboard or their experience level. I would, however, like to see a change in far 135 requiring 2 pilots on any/all passenger carrying flts in multi engine aircraft.

Related reports:

Google
 

Original NASA ASRS Text

Title: LIFEGUARD FLT CLIMBS THROUGH ASSIGNED ALT.

Narrative: DURING CLB OUT OF FWA, I WAS SHOWING AN AREA OF TSTMS AND DEVELOPING TSTMS JUST TO THE N OF MY INTENDED COURSE. I WAS LEVEL AT 3000' WHEN I ASKED FWA DEP FOR A DEVIATION TO THE S. THE DEVIATION WAS APPROVED AND I WAS INSTRUCTED TO CLB AND MAINTAIN 4000'. THE AUTOPLT WAS ENGAGED AND I SET IT TO LEVEL OFF AT 4000'. I WAS VERY BUSY AT THIS POINT, OPERATING THE RADAR AND STUDYING THE ENRTE CHART FOR A NEW RTE OF FLT AND DEST. AT 3800', I TRIMMED THE AUTOPLT FOR ABOUT A 200 FPM CLB. I CONTINUED WORKING WITH THE RADAR AND ENRTE CHART. A FEW MINS LATER, FWA ADVISED ME THAT MY MODE C INDICATED 4500' AND ASKED IF I WANTED 5000' AS A FINAL ALT. I SAID THAT 4000' WOULD BE FINE AND APOLOGIZED FOR THE ALT DEVIATION. SOME FACTORS WHICH I BELIEVE CONTRIBUTED TO THIS INCIDENT WERE: 1) LACK OF A SECOND PLT/RELIANCE ON THE AUTOPLT. 2) THE AREA OF TSTMS/TURB WHICH I WAS DEVIATING AROUND. 3) THE IMPORTANCE OF THE AIR AMBULANCE FLT WHICH LED ME TO FLYING NEAR AN AREA OF SEVERE TSTMS. 4) THIS WAS MY SECOND CHARTER FLT OF THE DAY AND I HAD BEEN ON DUTY OVER 9 HRS AT THE TIME OF THE INCIDENT. I DON'T KNOW WHAT CAN BE DONE TO PREVENT ALT DEVIATIONS IN THE FUTURE. THEY SEEM TO HAPPEN IN ALL ACFT REGARDLESS OF THE # OF PLTS ABOARD OR THEIR EXPERIENCE LEVEL. I WOULD, HOWEVER, LIKE TO SEE A CHANGE IN FAR 135 REQUIRING 2 PLTS ON ANY/ALL PAX CARRYING FLTS IN MULTI ENG ACFT.

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.