What happened
On April 19, 2005, an AVRO 146-RJ 100, registration HB-IXN, operated by Swiss International Air Lines, was performing a scheduled flight from Munich to Zurich. During the descent to approximately 13,000 feet, a pungent odor and a visible haze began to fill the cockpit. The situation was caused by an oil leak originating from a bearing failure in engine number one.
As the haze intensified, the co-pilot began to feel unwell and immediately donned an oxygen mask. The captain, while feeling physically fine, did not use a mask. The crew requested landing priority at Zurich-Kloten due to the deteriorating air quality in the flight deck. During the approach, the co-post was significantly impaired by the toxic fumes, and the captain eventually had to switch from autopilot to manual flight to complete the landing. Upon arrival, the aircraft was met by airport fire services, though the passengers were able to disembark normally.
The investigation
SUST examined the maintenance history of the aircraft, noting that similar issues involving oil smells and white smoke had been reported on previous flights, including a flight on April 18. Maintenance records showed that while oil traces were found on the air conditioning pack in Düsseldorf, subsequent inspections in Zurich failed to identify the underlying bearing failure in engine number one.
Investigators found that the maintenance team had reactivated air conditioning pack 1 without explicitly documenting this change in the work orders, meaning the crew was not clearly informed of the system's status. Furthermore, while engine number one had shown increasing oil consumption, a high-power engine run-up—which likely would have revealed the leak—was not performed.
Findings
- The cockpit was filled with a haze that had toxic effects, resulting in the limited operational capability of the co-pilot.
- The haze was produced by an oil leak caused by a bearing failure in engine number one.
- Indicators of the impending bearing failure, such as increased oil consumption and previous reports of smells, were not properly analyzed or followed up by maintenance.
- The aircraft was released for flight multiple times despite the unresolved underlying issue.
- The captain failed to use an oxygen mask despite the visible haze and the co-pilot's physical distress.
- The maintenance documentation did not clearly communicate the operational status of the air conditioning system to the flight crew.