What happened
On 1 May 1998, a Jetstream 4/100, registration G-MAJI, was undergoing an engine start sequence at Southampton Airport during a public transport flight. While attempting to start the right-hand engine, the crew observed a loud bang accompanied by sparks emerging from the engine cowling. The commander immediately ordered the First Officer to abort the start procedure.
Following the incident, smoke was observed venting from the cowling holes. Ground engineers advised the flight deck to shut down the aircraft, and all electrical systems were deactivated. Although smoke remained visible from the right engine cowling while passengers were being evacuated, all 24 passengers and 3 crew members disembarked safely and without injury. The smoke eventually ceased during the evacuation process.
The investigation
An inspection of the right engine revealed significant heat damage to the electrical terminal block of the starter/generator, along with damaged supply cables. Investigators discovered that a rag had been left inside the lower engine cowling; this material had been ignited by molten metal fragments that fell from the terminal block.
Detailed examination of the starter/generator unit at an approved overhaul facility revealed that the positive terminal had been incorrectly assembled. A large spacer washer, made of mild steel, had been placed between the stator lug and the cable eye end. This placement created high resistance by reducing the effective contact area, leading to overheating and arcing. Additionally, the required lock washer was missing, and the terminals lacked identifying marks to distinguish between positive and negative connections.
Maintenance records indicated that the starter/generator had been installed during an engine change in March 1998. While a torque value was recorded, the specific task of electrical connection lacked a mechanic's signature. The investigation also noted that while the manufacturer had issued instructions for correct assembly, the Illustrated Parts Catalogue (IPC) contained an incorrect illustration that mirrored the faulty assembly found on the aircraft.
Findings
- The fire was caused by the ignition of a rag left in the engine cowling by molten metal from the terminal block.
- Incorrect assembly of the starter/generator terminal block caused high resistance, overheating, and arcing.
- The use of a mild steel spacer washer in the electrical path reduced the contact area.
- The absence of a lock washer and the lack of identifying marks on the terminals contributed to the failure.
- Inaccurate illustrations in the manufacturer's Illustrated Parts Catalogue (IPC) provided misleading assembly guidance.