Incident Overview
On 17 September 2003, a Saab 2000 aircraft (registration HB-IZJ) operated by Swiss International Air Lines as flight LX 1018 from Zurich to Düsseldorf encountered an unusual smell during the climb phase. The incident occurred at approximately 12:35 local time over Lake Constance at flight level 140. The aircraft was climbing via the BODAN departure route when the copilot detected a smell described as reminiscent of hot oil evaporating. The commander and a flight attendant corroborated the observation. No smoke, fumes, or visible contaminants were present, and visibility remained unaffected.
Flight Details
The flight departed Zurich at 10:21:37 UTC from runway 28. During the climb, troubleshooting procedures were initiated. The flight crew cycled the air conditioning packs and bleed air systems individually, which caused the smell to shift between the cockpit and cabin. The odor varied in intensity and caused mild eye irritation in the copilot and flight attendant, but no respiratory irritation. Oxygen masks were not required. The crew searched the cabin for the source, noting an acrid smell near the avionics compartment. After approximately 10 minutes of troubleshooting, the crew decided to return to Zurich. No emergency was declared. Air traffic control approved a left turn via SULZ. The passengers were informed of a technical problem. The smell persisted intermittently during descent, intensifying below FL 150. The aircraft landed uneventfully at approximately 11:14 UTC, 52 minutes after departure. Passengers deplaned normally.
Technical Findings
Post-incident inspections revealed no external damage or obvious leak sources. Visual checks of both engines for oil leaks were negative. However, a flight test confirmed an oil smell originating from the left engine during descent with the power lever at flight idle and the right pack off. The left engine was subsequently replaced. Disassembly of the left engine (Allison AE2100A) showed that the seal coating on the 10th stage compressor vane ring assembly was partially missing due to scratches and breakouts. The bleed air for cabin pressurization is taken from the 14th stage at low power and from the 9th stage at high power. The bearing seals are carbon seals tightened by compressor air. The manufacturer noted that missing coating on similar vane rings is a known issue on Rolls-Royce AE3007 engines, but no corresponding recommendation existed for the AE2100A at the time. No determination of the root cause for the coating loss was provided by the manufacturer.
Investigation Results
The investigation concluded that the contaminating smell likely resulted from oil residue on the left engine's compressor components, which entered the cabin air supply system via bleed air. The aircraft had a history of smell-related maintenance entries, including oil, paint, and electrical odors, but none were linked to the current event. No birdstrike or other damage was found to be causal. The aircraft sustained no damage, and no injuries were reported.