Narrative:

I was on an IFR flight plan from columbus, oh to yng. At approximately 30 NM northwest of yng was cleared to ZOB from 13000 to 11000'. During descent was further cleared to 9000', plus given a frequency change to yng approach. Checked in with yng approach and stated out of 11000 for 9000'. Entered IMC conditions with light to moderate turbulence, precipitation and light rime icing. Approaching 9000' and only 14 NM from airport, passenger appeared in aisle behind me. Passenger inquired whether or not he could relocate to vacant copilot's seat. My attention was diverted to requesting passenger situation back down and I allowed aircraft's altitude to descend through 9000' to approximately 8400. Approach controller then called to to verify my altitude. I immediately began ascent to 9000', but controller told me to maintain 8000', and before I reached 8000, further cleared the aircraft to 3000'. This situation occurred due to my distraction with dealing with my passenger, plus the high descent rates I was experiencing due to my close proximity to the airport. Further complications were the turbulent IMC conditions at the time. I suggest that pilots, especially during single pilot operation in high performance aircraft, exercise extreme diligence during climbs and dscnts. I would further suggest that passenger be informed during preflight briefings to observe the seat belt signs posted by the pilot and not attempt to communicate with the pilot during critical phases of flight.

Related reports:

Google
 

Original NASA ASRS Text

Title: CPR LTT ALT DEVIATION OVERSHOT DURING DESCENT. A PASSENGER HAD COME FORWARD ASKING TO SIT IN THE FO SEAT.

Narrative: I WAS ON AN IFR FLT PLAN FROM COLUMBUS, OH TO YNG. AT APPROX 30 NM NW OF YNG WAS CLRED TO ZOB FROM 13000 TO 11000'. DURING DSCNT WAS FURTHER CLRED TO 9000', PLUS GIVEN A FREQ CHANGE TO YNG APCH. CHKED IN WITH YNG APCH AND STATED OUT OF 11000 FOR 9000'. ENTERED IMC CONDITIONS WITH LIGHT TO MODERATE TURB, PRECIPITATION AND LIGHT RIME ICING. APCHING 9000' AND ONLY 14 NM FROM ARPT, PAX APPEARED IN AISLE BEHIND ME. PAX INQUIRED WHETHER OR NOT HE COULD RELOCATE TO VACANT COPLT'S SEAT. MY ATTN WAS DIVERTED TO REQUESTING PAX SIT BACK DOWN AND I ALLOWED ACFT'S ALT TO DSND THROUGH 9000' TO APPROX 8400. APCH CTLR THEN CALLED TO TO VERIFY MY ALT. I IMMEDIATELY BEGAN ASCENT TO 9000', BUT CTLR TOLD ME TO MAINTAIN 8000', AND BEFORE I REACHED 8000, FURTHER CLRED THE ACFT TO 3000'. THIS SITUATION OCCURRED DUE TO MY DISTR WITH DEALING WITH MY PAX, PLUS THE HIGH DSCNT RATES I WAS EXPERIENCING DUE TO MY CLOSE PROX TO THE ARPT. FURTHER COMPLICATIONS WERE THE TURBULENT IMC CONDITIONS AT THE TIME. I SUGGEST THAT PLTS, ESPECIALLY DURING SINGLE PLT OPERATION IN HIGH PERFORMANCE ACFT, EXERCISE EXTREME DILIGENCE DURING CLBS AND DSCNTS. I WOULD FURTHER SUGGEST THAT PAX BE INFORMED DURING PREFLT BRIEFINGS TO OBSERVE THE SEAT BELT SIGNS POSTED BY THE PLT AND NOT ATTEMPT TO COMMUNICATE WITH THE PLT DURING CRITICAL PHASES OF FLT.

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.