Narrative:

Aircraft had been level at FL410. Autoplt was on and aircraft pitched up with no input from pilot or copilot. No inadvertent control input was made. Noticed proline alerter flashing; notating that we had deviated from altitude of FL410. Immediately advised PF to check altitude. First assumed autoplt had been accidentally disconnected as control inputs would not arrest climb. PF then disconnected autoplt and manually pitched back down to FL410 level trimmed aircraft back to FL410 (we had reached FL417). Aircraft had entered sharp pitch-up attitude with no indication of runaway trim! Immediately advised ATC of our deviation and initially put the problem down to autoplt had disconnected; but it had malfunctioned. ATC advised no traffic conflict. We had no reoccurrence of this event for the remainder of the flight. This particular aircraft had a similar problem (only once) when we had operated the aircraft for about 6 months or 200 hours. Now having over 4 yrs of flying this aircraft (serial number specific) am well aware of the operating characteristic of this aircraft and this problem has now just repeated itself. This was a complete anomaly with loss of airspeed that immediately lost 25 KTS of speed and again of 600 ft before the climb could be arrested. We attempted to recollect our actions and any pilot input that would have caused the event; but could not come to any conclusion. Also we looked at mountain wave as a possibility; but had experienced very minor fluctuation with minor airspeed deviation (+/-5 KTS). As a result of this action I will be contacting my cessna citation field service rep and advising of this incident to seek a course of action. Also I have read that there is pending arguments for audible trim runaway alert. This may have been attributed to autoplt pitch trim; but PIC in left seat did not recall erratic trim wheel motion. Did not recall hearing audio altitude alert going off. I noticed recently that the NTSB had recommended audible trim alert on earlier citation aircraft and the similar trim system is also characteristics of this aircraft. It may have a trim runaway that only visual clues led me to see this problem and an audible trim alert would have prevented such radical altitude deviation. Aircraft is equipped with single pfd and dual pfd displays may have caught the altitude deviation little sooner. 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 flight level change; or it will pitch the nose up or down with the autopilot engaged. Such activation will depart an altitude. Its location on the center console is vulnerable to inadvertent activation. In addition; the pitch trim in this aircraft is constantly trimming during cruise; without any airspeed change.

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Original NASA ASRS Text

Title: C525 PITCHED UP DURING CRUISE; WITHOUT INPUT FROM EITHER PLT.

Narrative: ACFT HAD BEEN LEVEL AT FL410. AUTOPLT WAS ON AND ACFT PITCHED UP WITH NO INPUT FROM PLT OR COPLT. NO INADVERTENT CTL INPUT WAS MADE. NOTICED PROLINE ALERTER FLASHING; NOTATING THAT WE HAD DEVIATED FROM ALT OF FL410. IMMEDIATELY ADVISED PF TO CHK ALT. FIRST ASSUMED AUTOPLT HAD BEEN ACCIDENTALLY DISCONNECTED AS CTL INPUTS WOULD NOT ARREST CLB. PF THEN DISCONNECTED AUTOPLT AND MANUALLY PITCHED BACK DOWN TO FL410 LEVEL TRIMMED ACFT BACK TO FL410 (WE HAD REACHED FL417). ACFT HAD ENTERED SHARP PITCH-UP ATTITUDE WITH NO INDICATION OF RUNAWAY TRIM! IMMEDIATELY ADVISED ATC OF OUR DEV AND INITIALLY PUT THE PROB DOWN TO AUTOPLT HAD DISCONNECTED; BUT IT HAD MALFUNCTIONED. ATC ADVISED NO TFC CONFLICT. WE HAD NO REOCCURRENCE OF THIS EVENT FOR THE REMAINDER OF THE FLT. THIS PARTICULAR ACFT HAD A SIMILAR PROB (ONLY ONCE) WHEN WE HAD OPERATED THE ACFT FOR ABOUT 6 MONTHS OR 200 HRS. NOW HAVING OVER 4 YRS OF FLYING THIS ACFT (SERIAL NUMBER SPECIFIC) AM WELL AWARE OF THE OPERATING CHARACTERISTIC OF THIS ACFT AND THIS PROB HAS NOW JUST REPEATED ITSELF. THIS WAS A COMPLETE ANOMALY WITH LOSS OF AIRSPD THAT IMMEDIATELY LOST 25 KTS OF SPD AND AGAIN OF 600 FT BEFORE THE CLB COULD BE ARRESTED. WE ATTEMPTED TO RECOLLECT OUR ACTIONS AND ANY PLT INPUT THAT WOULD HAVE CAUSED THE EVENT; BUT COULD NOT COME TO ANY CONCLUSION. ALSO WE LOOKED AT MOUNTAIN WAVE AS A POSSIBILITY; BUT HAD EXPERIENCED VERY MINOR FLUCTUATION WITH MINOR AIRSPD DEV (+/-5 KTS). AS A RESULT OF THIS ACTION I WILL BE CONTACTING MY CESSNA CITATION FIELD SVC REP AND ADVISING OF THIS INCIDENT TO SEEK A COURSE OF ACTION. ALSO I HAVE READ THAT THERE IS PENDING ARGUMENTS FOR AUDIBLE TRIM RUNAWAY ALERT. THIS MAY HAVE BEEN ATTRIBUTED TO AUTOPLT PITCH TRIM; BUT PIC IN L SEAT DID NOT RECALL ERRATIC TRIM WHEEL MOTION. DID NOT RECALL HEARING AUDIO ALT ALERT GOING OFF. I NOTICED RECENTLY THAT THE NTSB HAD RECOMMENDED AUDIBLE TRIM ALERT ON EARLIER CITATION ACFT AND THE SIMILAR TRIM SYS IS ALSO CHARACTERISTICS OF THIS ACFT. IT MAY HAVE A TRIM RUNAWAY THAT ONLY VISUAL CLUES LED ME TO SEE THIS PROB AND AN AUDIBLE TRIM ALERT WOULD HAVE PREVENTED SUCH RADICAL ALTDEV. ACFT IS EQUIPPED WITH SINGLE PFD AND DUAL PFD DISPLAYS MAY HAVE CAUGHT THE ALTDEV LITTLE SOONER. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THAT SINCE THE ACFT IS CERTIFIED SINGLE-PILOT; THIS ACFT WAS DELIVERED WITH A PFD ONLY ON THE LEFT SIDE. THE RIGHT PILOT 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 FLT LEVEL CHANGE; OR IT WILL PITCH THE NOSE UP OR DOWN WITH THE AUTOPILOT ENGAGED. SUCH ACTIVATION WILL DEPART AN ALT. ITS LOCATION ON THE CENTER CONSOLE IS VULNERABLE TO INADVERTENT ACTIVATION. IN ADDITION; THE PITCH TRIM IN THIS ACFT IS CONSTANTLY TRIMMING DURING CRUISE; WITHOUT ANY AIRSPEED CHANGE.

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.