Narrative:

We fly a C414 with equipment suffix 'golf.' on sep/sat/97, we were on an IFR flight from oakland international to san diego montgomery field. We fly our C414 strictly on IFR flight plans. At the time of the situation we were cruising at 17000 ft, and ATC had modified our flight plan to go from seal beach via victor 23 to mission bay. While on this leg of our flight, it appears that the autoplt interface with the autotrim malfunctioned (our best guess), giving us a nose down pitch. When we noticed this situation, we immediately disconnected the autoplt and trim, but by that time, had lost 200-300 ft. We immediately began to correct the altitude and simultaneously with our commencement of altitude correction to go back to our flying level of 17000 ft, ATC informed us that we were 500 ft off our assigned altitude, and that they had received an 'altitude alert' as she put it. Within seconds we had corrected for the problem and disengaged the autotrim entirely by turning it off and pulling the circuit breaker. The rest of the flight went on without event and we landed at montgomery field. The time of this event was late morning. In late afternoon, we went back to the aircraft for our return flight from montgomery field to oakland international. We had pre-filed for the return trip, and when we called flight service for the plan, we were informed that they could not find it in the computer. (I had checked in the morning before departure and they confirmed that they had both flight plans.) therefore, a new flight plan was filed. When we taxied out to the run-up area and were trying to get our clearance, ground control asked us whether we had been informed that ZLA wanted us to call them, via their supervisor. We informed them that we had not received this message but would be happy to call the supervisor upon our landing at oakland. Our return flight was uneventful, and upon landing, we called the number given and asked for the supervisor, who idented himself as mr X. My copilot spoke to him and explained that we are both experienced pilots and that this was not a case of lackadaisically losing altitude, but was a situation caused by equipment malfunction, which was immediately isolated and taken out of the system. The copilot apologized for the situation and explained our concern and understanding to the approach controller's telling us about the altitude alert. The supervisor, mr X was extremely understanding, and indicated that these things happen and they had to follow through on it because the system requires it, and that probably nothing would come of this, although in some cases the FSDO might call to ask a few questions, but he thought it highly unlikely. Upon my return home, I decided to call mr X personally to reconfirm the explanation of the situation as given to him by my copilot, I explained to mr X how carefully we train and stay current and that we fly the airplane with great care and that I personally train annually with flight safety in long beach, ca. I also explained that my copilot is in cpr aviation and is an instrument and multi-engine instructor. The supervisor informed me that he appreciated how courteous the conversation was with my copilot and that we should not overreact to this. However, once again he commented that the FSDO might call. I informed him that as soon as possible, I would have our repair station check the problem out and correct it so that we did not have this problem in the future. My conversation with the supervisor ended on a positive note, understanding that the situation was caused by a mechanical problem, totally out of our control. He indicated that his written report would support the fact that it was, in his belief, a mechanical problem, totally out of our control.

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Original NASA ASRS Text

Title: C414 PLT HAS PROB WITH AUTOPLT INTERFACE WITH THE AUTOTRIM MALFUNCTIONING. THIS CAUSES AN ALT LOSS OF 200- 300 FT AND ACTIVATES AN ALT ALERT AT ATC. THE PROB IS SOLVED BY PULLING THE CIRCUIT BREAKER.

Narrative: WE FLY A C414 WITH EQUIP SUFFIX 'GOLF.' ON SEP/SAT/97, WE WERE ON AN IFR FLT FROM OAKLAND INTL TO SAN DIEGO MONTGOMERY FIELD. WE FLY OUR C414 STRICTLY ON IFR FLT PLANS. AT THE TIME OF THE SIT WE WERE CRUISING AT 17000 FT, AND ATC HAD MODIFIED OUR FLT PLAN TO GO FROM SEAL BEACH VIA VICTOR 23 TO MISSION BAY. WHILE ON THIS LEG OF OUR FLT, IT APPEARS THAT THE AUTOPLT INTERFACE WITH THE AUTOTRIM MALFUNCTIONED (OUR BEST GUESS), GIVING US A NOSE DOWN PITCH. WHEN WE NOTICED THIS SIT, WE IMMEDIATELY DISCONNECTED THE AUTOPLT AND TRIM, BUT BY THAT TIME, HAD LOST 200-300 FT. WE IMMEDIATELY BEGAN TO CORRECT THE ALT AND SIMULTANEOUSLY WITH OUR COMMENCEMENT OF ALT CORRECTION TO GO BACK TO OUR FLYING LEVEL OF 17000 FT, ATC INFORMED US THAT WE WERE 500 FT OFF OUR ASSIGNED ALT, AND THAT THEY HAD RECEIVED AN 'ALT ALERT' AS SHE PUT IT. WITHIN SECONDS WE HAD CORRECTED FOR THE PROB AND DISENGAGED THE AUTOTRIM ENTIRELY BY TURNING IT OFF AND PULLING THE CIRCUIT BREAKER. THE REST OF THE FLT WENT ON WITHOUT EVENT AND WE LANDED AT MONTGOMERY FIELD. THE TIME OF THIS EVENT WAS LATE MORNING. IN LATE AFTERNOON, WE WENT BACK TO THE ACFT FOR OUR RETURN FLT FROM MONTGOMERY FIELD TO OAKLAND INTL. WE HAD PRE-FILED FOR THE RETURN TRIP, AND WHEN WE CALLED FLT SVC FOR THE PLAN, WE WERE INFORMED THAT THEY COULD NOT FIND IT IN THE COMPUTER. (I HAD CHKED IN THE MORNING BEFORE DEP AND THEY CONFIRMED THAT THEY HAD BOTH FLT PLANS.) THEREFORE, A NEW FLT PLAN WAS FILED. WHEN WE TAXIED OUT TO THE RUN-UP AREA AND WERE TRYING TO GET OUR CLRNC, GND CTL ASKED US WHETHER WE HAD BEEN INFORMED THAT ZLA WANTED US TO CALL THEM, VIA THEIR SUPVR. WE INFORMED THEM THAT WE HAD NOT RECEIVED THIS MESSAGE BUT WOULD BE HAPPY TO CALL THE SUPVR UPON OUR LNDG AT OAKLAND. OUR RETURN FLT WAS UNEVENTFUL, AND UPON LNDG, WE CALLED THE NUMBER GIVEN AND ASKED FOR THE SUPVR, WHO IDENTED HIMSELF AS MR X. MY COPLT SPOKE TO HIM AND EXPLAINED THAT WE ARE BOTH EXPERIENCED PLTS AND THAT THIS WAS NOT A CASE OF LACKADAISICALLY LOSING ALT, BUT WAS A SIT CAUSED BY EQUIP MALFUNCTION, WHICH WAS IMMEDIATELY ISOLATED AND TAKEN OUT OF THE SYS. THE COPLT APOLOGIZED FOR THE SIT AND EXPLAINED OUR CONCERN AND UNDERSTANDING TO THE APCH CTLR'S TELLING US ABOUT THE ALT ALERT. THE SUPVR, MR X WAS EXTREMELY UNDERSTANDING, AND INDICATED THAT THESE THINGS HAPPEN AND THEY HAD TO FOLLOW THROUGH ON IT BECAUSE THE SYS REQUIRES IT, AND THAT PROBABLY NOTHING WOULD COME OF THIS, ALTHOUGH IN SOME CASES THE FSDO MIGHT CALL TO ASK A FEW QUESTIONS, BUT HE THOUGHT IT HIGHLY UNLIKELY. UPON MY RETURN HOME, I DECIDED TO CALL MR X PERSONALLY TO RECONFIRM THE EXPLANATION OF THE SIT AS GIVEN TO HIM BY MY COPLT, I EXPLAINED TO MR X HOW CAREFULLY WE TRAIN AND STAY CURRENT AND THAT WE FLY THE AIRPLANE WITH GREAT CARE AND THAT I PERSONALLY TRAIN ANNUALLY WITH FLT SAFETY IN LONG BEACH, CA. I ALSO EXPLAINED THAT MY COPLT IS IN CPR AVIATION AND IS AN INST AND MULTI-ENG INSTRUCTOR. THE SUPVR INFORMED ME THAT HE APPRECIATED HOW COURTEOUS THE CONVERSATION WAS WITH MY COPLT AND THAT WE SHOULD NOT OVERREACT TO THIS. HOWEVER, ONCE AGAIN HE COMMENTED THAT THE FSDO MIGHT CALL. I INFORMED HIM THAT AS SOON AS POSSIBLE, I WOULD HAVE OUR REPAIR STATION CHK THE PROB OUT AND CORRECT IT SO THAT WE DID NOT HAVE THIS PROB IN THE FUTURE. MY CONVERSATION WITH THE SUPVR ENDED ON A POSITIVE NOTE, UNDERSTANDING THAT THE SIT WAS CAUSED BY A MECHANICAL PROB, TOTALLY OUT OF OUR CTL. HE INDICATED THAT HIS WRITTEN RPT WOULD SUPPORT THE FACT THAT IT WAS, IN HIS BELIEF, A MECHANICAL PROB, TOTALLY OUT OF OUR CTL.

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.