Incident Description
On 1 May 1998 at 1550 UTC, a Jetstream 4100 (registration G-MAJI) operated a public transport flight from Southampton Airport. During the start cycle of the right engine, the engine accelerated slowly. A loud bang and sparks from the engine cowling prompted the commander to order the first officer to abort the start. Smoke appeared from cowling vent holes. The ground engineer advised shutting down the aircraft, and all electrical systems were turned off. Passengers disembarked safely, and the smoke stopped.
Investigation Findings
Inspection revealed severe heat damage to the starter/generator's main electrical terminal block. The positive supply cable was disconnected from the 'B' terminal; its eye end had partially burnt away. Smoke originated from a rag left in the lower engine cowling, ignited by molten metal from the terminal block. The starter/generator was removed and examined at an approved overhaul facility. The examination found that the B (positive) terminal had been incorrectly assembled: the large spacer washer was fitted between the stator lug and the supply cable eye end, making the mild steel spacer part of the electrical current path. This reduced contact area, causing high resistance, overheating, arcing, and melting. Additionally, the lock washer was missing. Both positive and negative terminals were identical and unmarked.
Maintenance and Manufacturer Actions
Maintenance records indicated the starter/generator was last worked on in late March 1998 during an engine replacement. The relevant worksheet lacked a mechanic's signature for the task of electrically connecting the starter/generator, though a torque value and inspector's stamp were present. The inspector could not recall the task. The manufacturer had issued Service Information Leaflet (SIL) 24-005 in October 1996 describing correct terminal build-up, valid for 12 months. In April 1997, the operator issued a technical instruction based on the SIL. However, the manufacturer's Illustrated Parts Catalogue (IPC) showed an incorrect assembly order similar to the one found. Following the investigation, the aircraft manufacturer re-issued SIL 24-005 with diagrams, issued SIL 20-002 reminding operators not to use the IPC for maintenance, revised the AMM, corrected the IPC illustration, and introduced labels on starter/generator units with terminal build-up and torque values.