Date: 201307
Local time of day: 1201-1800
Location: ZZZ.TRACON, US
Flight conditions: IMC
Weather elements / visibility: Rain; 0
Light: Daylight
Aircraft: King Air C90 E90
Operator: Air Taxi
Operating under: Part 135
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class E ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Autoflight System
Component problem: Improperly Operated
Reporter organization: Air Taxi
Reporter function: Captain; Single Pilot; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor
Human factors: Human-Machine Interface; Workload; Distraction
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Undershoot; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Detector: Automation Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Contributing factors: Procedure; Aircraft; Human Factors
Primary problem: Human Factors

Narrative: While in level flight at 6;000 FT MSL in IMC I was directed by ATC to climb and maintain 11;000 FT.  During this phase of flight the autopilot was engaged and functioning normally.  I selected 11;000 on the altitude preselect and pressed the 'climb' function button on the autopilot control panel.  My attention was focused on programming the route assigned by ATC into the GPS immediately after; as I had received multiple vectors and two reroutes that differed from my originally assigned clearance in the ten minutes since takeoff.  When I looked up from my notes to program the next fix; I saw the airplane was in approximately 1;000 FT per minute descent.  I immediately disconnected the autopilot; leveled the aircraft; and began climbing.  The total altitude loss was approximately 500 FT.  As I passed through 6;000 FT MSL in the climb the Controller restated the instructions to climb and maintain 11;000 FT; which I acknowledged.  Total time of the deviation was less than 1 minute.  After regaining positive control of the aircraft; I reengaged the autopilot and verified that the 'climb' input was indicating on the display; and further verified the instrumentation indicated a climb.  The remainder of the flight continued without incident.  I believe that pilot error was the cause of the deviation.  The 'climb' and 'descend' function keys on the autopilot control panel are adjacent to one another.  I believe that I pressed the 'descend' key by mistake; and was so focused on programming the routing into the GPS that I failed to follow my normal procedure and verify that the proper function had been selected before allowing my attention to be diverted. Contributing factors include my lack of familiarity with the specific route being flown and the area airspace in general; the number of routing changes issued by ATC; and the generally high workload of single pilot IFR.  Additionally; the aural warning system installed in the plane provided no notice of the altitude deviation; but since I had selected a significantly higher altitude and then ordered a descent there was no reason it should have as it is designed to only provide warnings for 1;000 FT and 200 FT deviations from the selected altitude.  This deviation was an excellent demonstration of why following standard checklists and procedures at all times is important under IFR; or really any flight condition.  If I had taken less than 5 seconds to observe the autopilot display prior to returning to my notes on the assigned routing; I would have immediately seen the error and been able to correct it without any deviation.  This has served to reinforce the 'select; engage; verify' procedure I normally use with the autopilot. Going forward I believe that this incident will be a solid reminder to me that automation is only going to be as good as the input that it receives; and that even while the autopilot is flying the plane I need to ensure that it is doing so correctly before turning my attention elsewhere.




Synopsis: A BE9L pilot at 6;000 FT was cleared to climb to 11;000 FT but selected autopilot DESCEND which is adjacent to the CLIMB key and distracted while programming the GPS noticed the descent after 500 FT.