What happened
On July 31, 2015, a Bombardier DHC 8-402, registration G-FLBB, was climbing through 17,000 feet near the OLAPO reporting point in the Shannon FIR during a scheduled commercial flight from Ireland West Airport to Manchester. The flight crew first noticed unusual odors and fumes on the flight deck. Shortly after, the cabin crew reported that the forward toilet smoke alarm had activated and visible smoke was appearing near the cabin ceiling.
In response to the deteriorating conditions, the crew leveled the aircraft at 19,000 feet and donned oxygen masks. Smoke subsequently became visible on the flight deck, appearing to emanate from the panels near the commander's seat. The crew issued a PAN-PAN urgency call to Air Traffic Control and initiated an immediate descent to 10,000 feet. After evaluating nearby options, the crew diverted to Dublin Airport, landing safely at 17:41 UTC. There were no injuries among the 74 passengers or 4 crew members.
The investigation
Following the incident, maintenance personnel conducted troubleshooting two days later. During an engine start-up, significant smoke was observed exiting an engine vent and the drain mast, and a large quantity of oil was discovered within the engine ducting. A borescope inspection revealed that oil was leaking from the Handling Bleud-Off Valve (HBOV) on the No. 1 engine.
An overhaul of the engine in Hamburg identified that the No. 4 Bearing Key washer had suffered distress and fracture. This failure caused a high unbalance in the high-pressure rotor, which in turn damaged the carbon seals. This damage allowed oil to leak into the gas path and contaminate the secondary oil system, leading to the fumes entering the aircraft's ventilation.
Findings
- The primary cause of the smoke and fumes was the failure of carbon seals due to the rupture of the No. 4 Bearing Key washer in the No. 1 engine.
- The mechanical distress of the washer was caused by an unbalance in the high-pressure rotor.
- The engine manufacturer had previously identified similar occurrences involving this specific component, leading to the implementation of various service bulletins and, eventually, a redesigned "infinite life" washer.