Incident
The crew reported that during an attempted engine start, the No. 1 engine failed to gain ignition within the prescribed 25-second limit, and they aborted the start. Shortly thereafter, ground personnel reported that the engine had developed a tail pipe fire. Following emergency procedures, the fire persisted, and the captain ordered the aircraft evacuated. Four passengers received minor injuries during the evacuation.
Investigation
Investigation revealed that the 'B' ignition system was inoperative and had been placarded as such, while the 'A' system was functioning normally. Examination of the 'B' system identified a short in the harness between the exciter and the ignition plug. After replacement of the 'B' harness, both ignition systems and the engine performed normally during subsequent tests.
Findings
The tail pipe fire could be lit off following an attempted start on the 'B' system, with a subsequent second start or switch over to the 'A' system without purging the engine of the initial start fuel. Either sequence would result in torching.