What happened
On 17 September 2003, a Saab 2000 aircraft, registration HB-IZJ, operated by Swiss International Air Lines as flight LX 1018, was climbing through FL 140 over Lake Constance when the flight crew detected an unusual odor. The co-pilot described the smell as resembling hot oil evaporating in a pan, a sensation later confirmed by the commander and a flight attendant.
As the crew attempted to troubleshoot the issue by cycling the air conditioning packs and bleed air systems, the odor shifted between the cockpit and the cabin. The intensity of the smell fluctuative, causing slight eye irritation for the crew. During the climb, the crew also noted an acidulous scent in the cabin. Unable to identify the source, the flight crew decided to abandon the flight to Dusseldorf and return to Zurich. During the descent, the smell intensified, and the co-pilot experienced a light headache and further eye irritation. The aircraft landed safely in Zurich without any injuries to the 50 passengers or the crew.
The investigation
Investigators examined the aircraft's flight data and cockpit voice recorders, alongside a thorough mechanical inspection. Maintenance checks included inspecting the engines for oil leaks, checking the APU, and examining the air conditioning ducts. While no external oil leaks were found on the engines, the investigation revealed that the APU was overfilled with oil and evidence of birdstrikes was found on both engines.
Upon disassembling the left engine, investigators discovered that the seal-coating on the 10th stage compressor vane ring assembly was scratched and partially missing. Furthermore, the investigation looked into the history of the aircraft, noting several previous reports of various odors, including electrical and plastic smells, in the months leading up to the incident.
Findings
- The primary cause of the incident was the entry of contaminated air from the left engine into the aircraft cabin via the pressurization system.
- At high engine power, oil likely leaked from a bearing and reached the cabin through the bleed air system.
- During descent, incomplete combustion of fuel, caused by debris from the damaged vane ring coating interfering with fuel nozzles, likely contributed to the odor.
- The decision to abort the flight was appropriate given the unidentified nature of the odor.
- Identifying the specific source of various odors remains a significant challenge for flight crews.