What happened
Shortly after pushback from gate B-8, it was observed that the handle for the #2 engine door 2 right was not flush. In response to this finding, the #2 engine was shut down. During the process, ground maintenance personnel closed the door from the outside.
Following the engine shutdown, the aircraft cabin began to fill with dense smoke. The captain attempted to request a jetway via radio and through an open window, but no jetway operator was available to assist the aircraft. The aircraft had received clearance to move to gate B-20 for the evacuation. Because a jetway could not be provided, the crew and passengers performed an evacuation using emergency slides.
The investigation
An investigation into the smoke and electrical behavior determined that both the battery buss relay (R1) and the battery transfer relay (R2) had failed. When the #2 engine was shut down, the electrical transfer system took over the load. It was also noted that the flightcrew did not power the right bus from the APU. Additionally, it was found that ground personnel were not cross-trained to operate a jetway, which contributed to the inability to connect a jetway to the aircraft during the incident.