What happened
On 22 June 1998, a Boeing 757-2YO, registration G-OOOX, was operating a scheduled public transport flight from Larnaca, Cyprus, to Manchester, UK. While climbing through FL 255, the crew heard a loud bang accompanied by sparks originating from the overhead panel. Immediately following this event, the commander's airspeed indicator dropped to zero, the altimeter displayed an OFF flag, and several indicators on the Radio Distance Magnetic Indicator (RDMI) failed.
While the first officer maintained control of the aircraft, the crew observed various caution and advisory messages on the Engine Indication and Crew Alerting System (EICAS). The commander attempted to restore flight instruments by selecting the alternate air data source, but other failures persisted, including the loss of the VOR/DME controller, the centre ILS, and the standby attitude indicator.
The crew declared an emergency and initiated a return to Larnaca. During the descent, the flight director and autothrottle failed, and a 'Right IRS DC Fail' message appeared. The commander performed a manual, overweight landing at 96 tonnes. There were no fatalities and no injuries among the 206 passengers or 9 crew members.
The investigation
Technical examination of the aircraft identified that two wires located behind panel P11 had chafed against a bonding lead. This contact earthed the disconnect bracket to the fuselage, creating a short circuit. This electrical fault caused the AC standby bus power circuit breaker to trip, which resulted in the simultaneous loss of multiple flight systems.
Findings
- The primary cause of the electrical failure was faulty routing of the wiring loom, which allowed wires to chafe against a metal bracket.
- The resulting short circuit triggered the tripping of the AC standby bus circuit breaker.
- Damage to the aircraft was limited to minor electrical wiring repairs.
- Subsequent fleet inspections by the operator revealed one other aircraft with similar chafing damage and two others with insufficient clearance in the same area.