Narrative:

Aircraft was in cruise flight at FL410. I had just returned to cockpit from a convenience visit at the rear of the aircraft. Putting my seat belt back on and looked over at pilot's pfd and noticed the altitude alert flashing and the aircraft climbing. Advised pilot flying to arrest altitude and assisted in pushing controls over myself. It was apparent that the autopilot was still engaged and radical climb; 1000 FPM; has ensued. PF kicked off autopilot; pushed over nose and re-trimmed aircraft back to FL410. Monitored autopilot and no further problems arose. Upon deviation immediately advised ATC of altitude deviation and they advised no traffic conflicts. After the deviation we were attempting to reconcile the issue of why the aircraft had deviated from our altitude. Only possible solution was that I may have knocked the unguarded pitch control knob on the center console. The pitch control knob is located rear of the console and could have been bumped. As a solution to rectify this I would suggest putting something of a guard over this pitch trip to prevent movement; or relocation of the switch. Secondly; I would have noticed the altitude deviation easier if we had a secondary pfd with altitude alerter in the right side. I tend to monitor the primary pfd as a better source of information and less reliance on the display of the 'round' gauges on the co-pilot's side. I would have caught the action a little sooner. PF could have been a little more assertive with response. Maybe there was a reluctance to input major control input for passenger comfort! As a course of action when I am PF and in the left seat I guard the panel and throttle levers to prevent inadvertent input from anyone that may be leaving the seat or getting into the seat from the main cabin. There was no delay in contacting ATC.callback conversation with reporter revealed the following information: reporter stated that since the aircraft is certified single-pilot; this aircraft was delivered with a pfd only on the left side. The right pilot display consists of a standard instrument display. The only altitude alert for an altitude deviation is that incorporated into the pfd. The pitch control knob is frequently used and is located on the center console. This multifunction knob controls the rate set for vertical speed; will set an airspeed for flch; or it will pitch the nose up or down with the autopilot engaged. This function will depart an altitude set in the altitude alert command display. The reporter believes that this knob may have been bumped as he stepped out of the relatively small cockpit.

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Original NASA ASRS Text

Title: C525 PLT RETURNED TO COCKPIT TO DISCOVER THE ACFT IN A CLIMB AWAY FROM THE ASSIGNED ALT. PLT BELIEVES THE PITCH CONTROL KNOB MAY HAVE BEEN INADVERTENTLY MOVED AS HE LEFT COCKPIT.

Narrative: ACFT WAS IN CRUISE FLT AT FL410. I HAD JUST RETURNED TO COCKPIT FROM A CONVENIENCE VISIT AT THE REAR OF THE ACFT. PUTTING MY SEAT BELT BACK ON AND LOOKED OVER AT PLT'S PFD AND NOTICED THE ALTITUDE ALERT FLASHING AND THE ACFT CLBING. ADVISED PLT FLYING TO ARREST ALTITUDE AND ASSISTED IN PUSHING CONTROLS OVER MYSELF. IT WAS APPARENT THAT THE AUTOPILOT WAS STILL ENGAGED AND RADICAL CLB; 1000 FPM; HAS ENSUED. PF KICKED OFF AUTOPILOT; PUSHED OVER NOSE AND RE-TRIMMED ACFT BACK TO FL410. MONITORED AUTOPILOT AND NO FURTHER PROBLEMS AROSE. UPON DEVIATION IMMEDIATELY ADVISED ATC OF ALTITUDE DEVIATION AND THEY ADVISED NO TFC CONFLICTS. AFTER THE DEVIATION WE WERE ATTEMPTING TO RECONCILE THE ISSUE OF WHY THE ACFT HAD DEVIATED FROM OUR ALTITUDE. ONLY POSSIBLE SOLUTION WAS THAT I MAY HAVE KNOCKED THE UNGUARDED PITCH CONTROL KNOB ON THE CENTER CONSOLE. THE PITCH CONTROL KNOB IS LOCATED REAR OF THE CONSOLE AND COULD HAVE BEEN BUMPED. AS A SOLUTION TO RECTIFY THIS I WOULD SUGGEST PUTTING SOMETHING OF A GUARD OVER THIS PITCH TRIP TO PREVENT MOVEMENT; OR RELOCATION OF THE SWITCH. SECONDLY; I WOULD HAVE NOTICED THE ALTITUDE DEVIATION EASIER IF WE HAD A SECONDARY PFD WITH ALTITUDE ALERTER IN THE R SIDE. I TEND TO MONITOR THE PRIMARY PFD AS A BETTER SOURCE OF INFORMATION AND LESS RELIANCE ON THE DISPLAY OF THE 'ROUND' GAUGES ON THE CO-PILOT'S SIDE. I WOULD HAVE CAUGHT THE ACTION A LITTLE SOONER. PF COULD HAVE BEEN A LITTLE MORE ASSERTIVE WITH RESPONSE. MAYBE THERE WAS A RELUCTANCE TO INPUT MAJOR CONTROL INPUT FOR PAX COMFORT! AS A COURSE OF ACTION WHEN I AM PF AND IN THE L SEAT I GUARD THE PANEL AND THROTTLE LEVERS TO PREVENT INADVERTENT INPUT FROM ANYONE THAT MAY BE LEAVING THE SEAT OR GETTING INTO THE SEAT FROM THE MAIN CABIN. THERE WAS NO DELAY IN CONTACTING ATC.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT SINCE THE ACFT IS CERTIFIED SINGLE-PLT; THIS ACFT WAS DELIVERED WITH A PFD ONLY ON THE LEFT SIDE. THE R PLT DISPLAY CONSISTS OF A STANDARD INSTRUMENT DISPLAY. THE ONLY ALT ALERT FOR AN ALT DEVIATION IS THAT INCORPORATED INTO THE PFD. THE PITCH CONTROL KNOB IS FREQUENTLY USED AND IS LOCATED ON THE CENTER CONSOLE. THIS MULTIFUNCTION KNOB CONTROLS THE RATE SET FOR VERTICAL SPEED; WILL SET AN AIRSPEED FOR FLCH; OR IT WILL PITCH THE NOSE UP OR DOWN WITH THE AUTOPILOT ENGAGED. THIS FUNCTION WILL DEPART AN ALT SET IN THE ALT ALERT COMMAND DISPLAY. THE RPTR BELIEVES THAT THIS KNOB MAY HAVE BEEN BUMPED AS HE STEPPED OUT OF THE RELATIVELY SMALL COCKPIT.

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.