What happened
During a trip check, airport customer service personnel notified a mechanic that a longitudinal spring-lift power drive unit (PDU) powered roller in the center cargo bay was inoperative and positioned in the 'up' position. The mechanic proceeded to remove the powered rollers from the cargo compartment. At the time of this task, the mechanic did not have the McDonnell Douglas MD-11 Maintenance Manual available.
While the mechanic left the aircraft to retrieve a replacement powered roller, a crew change occurred within the airport customer service staff. The incoming crew was unaware that a cannon plug for the powered roller had been left on the cargo compartment floor. As the new crew began loading cargo bins, the bin ran over the cannon plug, resulting in the severing of its connecting wires.
Following this, a technician started the aircraft's auxiliary power unit (APU) to supply electrical power. During servicing, other technicians working in the cabin observed smoke and flames, measuring approximately 4 to 6 inches, emerging from behind a floor vent at row 12 of the main passenger cabin. The fire was eventually extinguished.