Date: 201210
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: A319
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class E ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Electrical Distribution Busbar
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Troubleshooting
Anomaly: Aircraft Equipment Problem Critical
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: General Maintenance Action; General Declared Emergency
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Aircraft was dispatched with the #2 Transformer/Rectifier (TR) on MEL. There was a lengthy and somewhat confusing follow up procedure associated with this MEL; so we requested the assistance of a mechanic to help us comply with the follow up procedures. The flight departed normally. While descending on the arrival; we received an 'Elect- DC buss 2 fault' message along with multiple systems failures. We followed the procedures; I transferred control of the aircraft to the First Officer; and did the ECAM procedures. We determined that landing distance was not an issue; informed the Dispatcher of the maintenance issue; and continued. At this time; we had a number of ECAM messages begin to appear and disappear in quick succession. There was not really time to identify each individual message before it disappeared and another message appeared. Then; it all stopped. I believe that DC bus #2 was resetting and faulting repeatedly. Given the multiple system failures associated with a DC bus 2 fault; we elected to declare an emergency as a precaution. Flight attendants were advised to expect a normal landing; but were alerted to the fact that emergency equipment might meet the aircraft. The passengers were also advised that; as a precaution; emergency equipment might meet the aircraft. The Captain resumed pilot flying duties after all procedures were completed; and an uneventful landing was made. Emergency equipment did not actually meet the aircraft. We taxied to the gate without incident. During the taxi in; the DC buss 2 reset for about one minute; then faulted again. Upon reaching the gate; the Captain called Dispatch and provided any information that he needed for his report. The Captain informed Maintenance that due to the intermittent nature of the fault; he would be reluctant to take the aircraft again until a definitive solution could be found to the problem. During troubleshooting on the ground; the Mechanic observed that when he reset the electrical system to normal with TR 2 functioning normally; DC bus 2 did not fault. When he configured the electrical system to comply with the MEL for an inoperative TR 2; DC bus 2 did fault. This is not the way it is supposed to be. Either there is something wrong with the aircraft; or there is something wrong with the MEL procedure. Verify that the MEL procedure for an inoperative TR 2 is not the cause of the DC bus 2 fault.




Synopsis: A319 Captain reports being dispatched with Transformer/Rectifier (TR) #2 on MEL and MEL procedures complied with. En route an ECAM for Elect- DC bus 2 fault message; along with multiple systems failures is received. The fault appears and resets multiple times during descent and approach. Maintenance is able to duplicate the fault at the gate but cannot find the cause. DC bus 2 operates normally with TR #2 operating. Reporter questions the MEL procedure.