Incident Overview
On 5 December 2005, at 08:56 UTC, an Avro 146-RJ100, registration HB-IXQ, operated by Swiss European Air Lines as flight LX 778, departed Zurich-Kloten Airport for a scheduled service to Brussels. Shortly after reaching flight level FL100, the commander noticed smoke near the left side console, which was also observed by the copilot and confirmed by a cabin crew member as present in the passenger cabin.
The flight crew immediately donned their oxygen masks. The commander, who was the pilot flying, transferred control to the copilot and declared an emergency at 09:02:39 UTC, requesting a return to Zurich for an approach to runway 14. During the descent and approach, the smoke dissipated. Throughout the event, the commander experienced a continuous flow of oxygen in his mask, which severely hampered communication with both the copilot and air traffic control; he was unable to stop the flow despite various adjustments.
The aircraft landed uneventfully at 09:16 UTC and taxied to the stand, where passengers disembarked normally.
Investigation Findings
The investigation by the Swiss Bureau of Aircraft Accident Investigation (BFU) determined that the smoke originated from an oil leak caused by a defective seal in the area of bearings No. 1 and 2 of engine No. 2. The oil leak allowed oil to enter the bleed air system, which then carried oil vapor into the cockpit and cabin.
Two days prior to the incident, on 3 December 2005, the crew had reported a recurring warning message "ENG 1 AIR VLV" in the technical log. Line maintenance action deferred the issue, and after the warning did not recur on subsequent flights, the work order was closed. However, the engineering department in Basel requested replacement of the affected temperature control valve, which was carried out on the night of 4–5 December 2005.
The crew had performed a "no bleeds take-off," using the auxiliary power unit (APU) for cabin and cockpit air conditioning. After passing 5,000 ft QNH, the copilot switched the bleed air source from the APU to the engines as part of the after take-off checklist. Shortly thereafter, the smoke appeared.
The commander reported observing both "ENG 1 AIR FAULT" and "ENG 1 AIR VALVE" caution indications around the time the smoke was noticed. He later turned off the bleed air from engine No. 1 and consulted the emergency checklist for smoke in the cockpit and cabin.
Cause
The serious incident was caused by smoke that spread into the cockpit and cabin shortly after takeoff from Zurich, resulting from an oil leak due to a defective seal in the area of bearings No. 1 and 2 of engine No. 2.