Airbus A300-600 Serious Incident Near Munich

Incident Overview and Aircraft Details On 3 December 2002, an Airbus A300-600 operated by a German airline was involved in a serious incident near Munich. The aircraft, which had been in service since April 1987, was equipped with a 'Theta Trim' Flight Augmentation Computer (FAC). At the time of the incident, the aircraft had accumulated 53,021 flight hours and 18,917 landings. The flight was a scheduled service from Munich to Frankfurt, carrying 189 passengers and 8 crew members. ## Sequence of Events During the climb to cruising altitude, the crew, using Autopilot 2 (AP 2), noticed that the aircraft was approaching its maximum operating speed (VMO). In response, they reduced the speed setting on the autopilot and selected a higher climb rate. However, the speed continued to increase, and the crew observed the nose of the aircraft pitching down. The autopilot was subsequently disengaged. When the pilot took manual control, the aircraft was heavily trimmed nose-down. It was no longer in a climb, and the speed had exceeded VMO by 16 knots. Significant control forces were required to manage the aircraft until the trim could be corrected using the electrical trim system. During the recovery, high vertical accelerations occurred, causing a flight attendant to fall and sustain minor injuries. The flight continued to its destination without further issues. ## Technical Investigation The investigation revealed that the issue was related to the Flight Augmentation Computer (FAC2). A cable break was found in the FAC2 slot, with a contact for the FAC2 retracted in the connector to the Flight Control Computer (FCC2) for AP 2. Further testing at the manufacturer identified a software deviation in the 'Theta Trim' modification. This deviation was present in all modified FACs delivered, affecting approximately 50 aircraft. The AUTOTRIM function itself was not altered, which is why it was not re-tested. The error was only detected during the investigation of this incident. ## Simulator Testing To reproduce the incident, the FCC2 and FAC2 from the affected aircraft were installed in an A300-600 simulator at the manufacturer's facility. With the simulator configured to match the cable break found in the aircraft, the incident was successfully reproduced. The tests showed that the signal for the tail horizontal stabilizer (THS) movement originated from the FAC2. The movement began when a certain airspeed was exceeded. The trim wheel and control column also moved, and the angle of attack on the Primary Flight Display (PFD) decreased, while the Flight Director (FD) commanded a pitch-up. A trend vector on the speed indicator also showed a further increase in speed. ## Maintenance and Regulatory Context Prior to the incident, the aircraft had experienced similar issues on 2 December 2002. On that day, the THS could only be adjusted when PTS 1 was off, and with AP 2 engaged, the THS was continuously trimmed nose-down. These issues were logged in the technical logbook. The PTS 1 issue was deferred under the Minimum Equipment List (MEL) due to time constraints. The PTS 2 issue was tested and cleared, with a note to monitor the problem. The aircraft was released for service on 3 December 2002. The investigation also noted that the software modification process for the FAC did not directly address changes to approved software, which may have contributed to the oversight.