What happened
On 28 July 1998, a Boeing 757-236, registration G-BPEE, was operating a public transport flight from London Heathrow to Belfast City Airport. During the cruise phase at Flight Level 2LL60 over the Isle of Man, the crew received a No. 2 engine fire warning, accompanied by the activation of the fire warning bell and cockpit lamps.
The crew immediately initiated the standard engine fire drill. After approximately 30 seconds, the crew discharged the second fire extinguishing bottle, after which the fire warning ceased. The aircraft continued to Belfast, where it landed without further incident. There were no fatalities and no injuries to the 168 passengers or 7 crew members on board.
The investigation
Post-flight engineering inspections of the right-hand engine revealed that the casing of the Integrated Drive Generator (IDG) had suffered an uncontained failure. This failure resulted in significant oil staining across the fan case, as well as fire damage to the engine wiring and the inner skin of the fan cowl.
Investigators found that the aircraft had arrived at Heathrow from Manchester with existing electrical warnings related to the No. 2 engine's IDG. Although the IDG had been disconnected and the aircraft was cleared for the flight to Belfast under a deferred defect entry, the investigation established that the IDG disconnect switch itself was malfunctioning. Specifically, the switch was found to operate intermittently, which prevented the successful disconnection of the unit. Additionally, the control panel housing the switches was identified as an older modification standard and was found to be causing stiffness in the No. 1 engine's disconnect switch.
Findings
- The primary cause of the engine damage was an uncontained failure of the IDG casing.
- The failure originated from a worn or failed generator rotor bearing within the IDG.
- The severity of the damage was exacerbated because the IDG disconnect switch failed to function correctly, preventing the crew from isolating the faulty unit.
- The generator rotor eventually impacted the stator, destroying both components and rupturing the casing, which released oil and debris.
- There was no reliable method for the flight crew or ground engineers to confirm whether the IDG had actually disconnected during the previous flight's maintenance actions.