What happened
During an attempted start of the number one engine, the crew reported that the engine failed to ignite within the prescribed 25-second limit. Consequently, they aborted the start procedure. Shortly after this event, ground personnel observed a fire developing in the engine tailpipe. Following emergency procedures, the captain ordered the aircraft to be evacuated. As a result of the evacuation, four passengers sustained minor injuries.
The investigation
Investigation revealed that the 'B' ignition system was inoperative and had been placarded as such at the time of the incident. The 'A' system was functioning normally. Examination of the equipment found a short in the 'B' system harness located between the exciter and the igniter plug. After the harness was replaced, both ignition systems and the engine performed normally.
Findings
The tailpipe fire could be ignited following an attempted start on the inoperative '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.