Piper PA42 pilot has an altitude deviation while in cruise flight.

Attributes
ACN	719576
Time
Date	200612
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : zjx.artcc
State Reference	FL
Altitude	msl single value : 26000
Environment
Flight Conditions	IMC
Weather Elements	Turbulence
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zjx.artcc
Operator	general aviation : personal
Make Model Name	PA-42 Cheyenne IIA
Operating Under FAR Part	Part 91
Navigation In Use	other
Flight Phase	cruise : level
Route In Use	enroute airway : j79.airway
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : multi engine pilot : private
Experience	flight time last 90 days : 25 flight time total : 1950 flight time type : 188
ASRS Report	719576
Person 2
Affiliation	government : foreign
Function	controller : radar
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to assigned altitude
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

I was flying south at FL260 (-19C) in IMC (high overcast clouds) with intermittent 'light chop' (turbulence) on J79 between milie intersection and omn. ATC had just given me another amendment to my routing which was to fly direct to mlb and then the blufi 1 (STAR) to opf. I had entered mlb in my GPS and punched 'direct' and adjusted the HSI course needle to the new course for the autoplt (autoplt was in the navigation mode with altitude hold engaged) to fly to mlb. After observing the airplane turning to the new course; I reached behind the copilot seat to place the H9 chart back into the chart rack (I already had H8 and L19 out) and picked up the florida terminal procedures from between the seats. I looked up the blufi 1 STAR to review it and ensure it was properly entered in the GPS. When I looked up at the panel the airplane was in a descending turn to the right and was already through 25700 ft. I immediately took the control wheel; leveled the wings; arrested the descent; and began a climbing turn back on course. As I was leveling at FL260 and just about back on course (airplane had drifted about 30 degrees to the right); ATC asked if I was experiencing any difficulty. I explained the autoplt had disengaged while I was reviewing the blufi 1 arrival on the just amended routing. When I got back on course and level at FL260 I re-engaged the autoplt and it functioned properly throughout the rest of the flight.

Original NASA ASRS Text

Title: PIPER PA42 PLT HAS AN ALTDEV WHILE IN CRUISE FLT.

Narrative: I WAS FLYING S AT FL260 (-19C) IN IMC (HIGH OVCST CLOUDS) WITH INTERMITTENT 'LIGHT CHOP' (TURB) ON J79 BTWN MILIE INTXN AND OMN. ATC HAD JUST GIVEN ME ANOTHER AMENDMENT TO MY ROUTING WHICH WAS TO FLY DIRECT TO MLB AND THEN THE BLUFI 1 (STAR) TO OPF. I HAD ENTERED MLB IN MY GPS AND PUNCHED 'DIRECT' AND ADJUSTED THE HSI COURSE NEEDLE TO THE NEW COURSE FOR THE AUTOPLT (AUTOPLT WAS IN THE NAV MODE WITH ALT HOLD ENGAGED) TO FLY TO MLB. AFTER OBSERVING THE AIRPLANE TURNING TO THE NEW COURSE; I REACHED BEHIND THE COPLT SEAT TO PLACE THE H9 CHART BACK INTO THE CHART RACK (I ALREADY HAD H8 AND L19 OUT) AND PICKED UP THE FLORIDA TERMINAL PROCS FROM BTWN THE SEATS. I LOOKED UP THE BLUFI 1 STAR TO REVIEW IT AND ENSURE IT WAS PROPERLY ENTERED IN THE GPS. WHEN I LOOKED UP AT THE PANEL THE AIRPLANE WAS IN A DSNDING TURN TO THE R AND WAS ALREADY THROUGH 25700 FT. I IMMEDIATELY TOOK THE CTL WHEEL; LEVELED THE WINGS; ARRESTED THE DSCNT; AND BEGAN A CLBING TURN BACK ON COURSE. AS I WAS LEVELING AT FL260 AND JUST ABOUT BACK ON COURSE (AIRPLANE HAD DRIFTED ABOUT 30 DEGS TO THE R); ATC ASKED IF I WAS EXPERIENCING ANY DIFFICULTY. I EXPLAINED THE AUTOPLT HAD DISENGAGED WHILE I WAS REVIEWING THE BLUFI 1 ARR ON THE JUST AMENDED ROUTING. WHEN I GOT BACK ON COURSE AND LEVEL AT FL260 I RE-ENGAGED THE AUTOPLT AND IT FUNCTIONED PROPERLY THROUGHOUT THE REST OF THE FLT.

Data retrieved from NASA's ASRS site as of January 2009 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.