Occurrence
On 26 October 2008, a Lufthansa Airbus A319 (registration D-AILF) operating flight LH3422 from Munich to Bucharest was in Hungarian airspace when the auxiliary power unit (APU) shut down automatically. The aircraft had been dispatched with a deferred generator failure on engine #2 under the terms of the Minimum Equipment List (MEL). The MEL required the APU to operate throughout the flight and the altitude not to exceed 33,500 feet. With the APU failure, these conditions were no longer met, and safe continuation was not assured. The crew decided to land at Budapest Ferihegy Airport without incident. After passengers disembarked, the aircraft taxied to the Lufthansa Technik Budapest (LHTB) maintenance area.
Investigation Findings
The Transportation Safety Bureau (TSB) investigated the incident. Prior to departure from Munich, a generator failure had been detected on engine #2 (right engine). This was documented as a deferred item record (DIR) in accordance with MEL paragraph 9.24-20-1, permitting a “C” repair interval (10 calendar days). The aircraft was released as airworthy, as recorded on Technical Log Book sheet T2192143. In flight, the APU automatically shut down at 33,000 feet, violating the MEL condition requiring APU operation throughout the flight. This led to the unplanned landing.
Post-flight, LHTB maintenance personnel printed the maintenance post-flight report and ECAM warning messages. Inspection of the APU revealed a fault in its electrical system that could not be corrected with minor disassembly. A new deferred item record was opened for the APU under MEL paragraph 9.49-10-1 with a “D” repair interval (120 calendar days), and the APU was deactivated. To restore the aircraft to service, the generator on engine #2 was replaced. A serviceability check after replacement showed no irregularities, and a leak check of the generator oil cooling system found no failures. The generator replacement was documented on Technical Log Book sheet T2192147, and the original deferred item for the generator failure was closed. The APU remained as an open status failure. The aircraft was then declared airworthy.
Safety Recommendations
No safety recommendations were issued, as the investigation did not reveal any circumstances warranting them.