Narrative:

At FL330 approximately 25 mi east of st johns VOR, we had leveled off at the center assigned altitude. The autoplt was engaged. The captain and myself noted a 150 ft variation in altitude, which is characteristic of this make of autoplt. Approximately 2 seconds after the altitude variation, we heard the audible trim þclicker,þ signifying that the internal pitch trim was in transit. Approximately 1 1/2 seconds after the clicker began, the altitude hold disengaged itself. The aircraft then began an immediate, abrupt climb. The captain immediately, and aggressively, began a pushover, using the autoplt pitch trim wheel. Realizing that the mach.82 speed limitation would be exceeded, he moved his right hand from the pitch trim wheel to the power levers in order to reduce thrust, and used his left hand while adjusting power with the right. The altitude alert was not heard by either crew member. ZAB asked us to verify our altitude as FL330. I responded that we were level at FL330, which was the indicated altitude at the time of the reply. There was a widebody transport at our 11 oþclock position, at approximately 5 mi, which we had in visual contact prior to and after the moment that the pitch trim began in motion. Upon transferring to the next ZAB sector, the controller advised us to call in reference to a þpossible altitude deviation.þ it should be noted that a very aggressive maneuver was initiated immediately upon detecting a problem in the pitch trim. Furthermore, visual contact with the widebody transport was never lost. Nor was proximity to the aircraft ever in question to either acftþs crew. I feel that, given the situation, the crew did everything humanly possible to avoid any further airspace incursions, especially given the exceptional climb performance of the light transport.

Related reports:

Google
 

Original NASA ASRS Text

Title: CPR LTT ACFT HAD AN ALTDEV CAUSED BY AN AUTOPLT MALFUNCTION. A WDB ACFT WAS NEARBY CAUSING LTSS. LTT PLTS TURNED OFF THE AUTOPLT TO CORRECT THE SEPARATION PROBLEM.

Narrative: AT FL330 APPROX 25 MI E OF ST JOHNS VOR, WE HAD LEVELED OFF AT THE CTR ASSIGNED ALT. THE AUTOPLT WAS ENGAGED. THE CAPT AND MYSELF NOTED A 150 FT VARIATION IN ALT, WHICH IS CHARACTERISTIC OF THIS MAKE OF AUTOPLT. APPROX 2 SECONDS AFTER THE ALT VARIATION, WE HEARD THE AUDIBLE TRIM þCLICKER,þ SIGNIFYING THAT THE INTERNAL PITCH TRIM WAS IN TRANSIT. APPROX 1 1/2 SECONDS AFTER THE CLICKER BEGAN, THE ALT HOLD DISENGAGED ITSELF. THE ACFT THEN BEGAN AN IMMEDIATE, ABRUPT CLB. THE CAPT IMMEDIATELY, AND AGGRESSIVELY, BEGAN A PUSHOVER, USING THE AUTOPLT PITCH TRIM WHEEL. REALIZING THAT THE MACH.82 SPD LIMITATION WOULD BE EXCEEDED, HE MOVED HIS R HAND FROM THE PITCH TRIM WHEEL TO THE PWR LEVERS IN ORDER TO REDUCE THRUST, AND USED HIS L HAND WHILE ADJUSTING PWR WITH THE R. THE ALT ALERT WAS NOT HEARD BY EITHER CREW MEMBER. ZAB ASKED US TO VERIFY OUR ALT AS FL330. I RESPONDED THAT WE WERE LEVEL AT FL330, WHICH WAS THE INDICATED ALT AT THE TIME OF THE REPLY. THERE WAS A WDB AT OUR 11 OþCLOCK POS, AT APPROX 5 MI, WHICH WE HAD IN VISUAL CONTACT PRIOR TO AND AFTER THE MOMENT THAT THE PITCH TRIM BEGAN IN MOTION. UPON TRANSFERRING TO THE NEXT ZAB SECTOR, THE CTLR ADVISED US TO CALL IN REF TO A þPOSSIBLE ALT DEV.þ IT SHOULD BE NOTED THAT A VERY AGGRESSIVE MANEUVER WAS INITIATED IMMEDIATELY UPON DETECTING A PROBLEM IN THE PITCH TRIM. FURTHERMORE, VISUAL CONTACT WITH THE WDB WAS NEVER LOST. NOR WAS PROX TO THE ACFT EVER IN QUESTION TO EITHER ACFTþS CREW. I FEEL THAT, GIVEN THE SITUATION, THE CREW DID EVERYTHING HUMANLY POSSIBLE TO AVOID ANY FURTHER AIRSPACE INCURSIONS, ESPECIALLY GIVEN THE EXCEPTIONAL CLB PERFORMANCE OF THE LTT.

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.