What happened
On December 13, 2003, an AVRO 146-RJ 100, registration HB-IXX, operated by Swiss International Air Lines, departed Zurich Airport for Düsseldorf. Approximately 12 minutes into the flight, while the aircraft was still in its climb phase, cabin crew reported the presence of a thick, fog-like smoke and a biting, acrid odor spreading through the mid-section of the cabin. The smell was also detectable on the right side of the cockpit.
Upon assessing the situation, the captain decided to abort the flight and return to Zurich. During the descent, the intensity of the smoke and odor began to dissipate. The aircraft landed safely at Zurich at 07:20 UTC, accompanied by airport fire services. The passengers and crew were able to disembark via the gate following standard procedures.
The investigation
The investigation focused on the recent maintenance performed on the aircraft's engines. Records showed that on the previous day, a bleed air valve on engine number 3 had been replaced. Investigators examined the aircraft's technical logs, cockpit voice recorder, and flight data recorder to reconstruct the sequence of events.
Post-landing inspections of the cabin and engine components were conducted. While visual inspections of the cabin ceiling and side panels showed no damage, investigators identified residue from a lubricant on an O-ring within the engine number 3 bleed air valve. The investigation also looked into the maintenance conditions, noting that the mechanic had performed the valve replacement alone on the apron at night, using only a flashlight and a single ladder, rather than in a hangar with a second technician.
Findings
- The smoke in the cabin was caused by the combustion of petroleum jelly residues within the bleed air valve.
- During the replacement of the bleed air valve, a mechanic used petroleum jelly to lubricate an O-ring to facilitate installation, despite technical instructions (info flash) explicitly prohibiting its use and mandating only soapy water.
- When the engines were operated at high power during the climb, these lubricant residues burned, sending smoke through the air conditioning system into the cabin.
- A required high-power ground engine run-up, which is intended to verify system integrity and burn off any such residues, was not performed due to time constraints and noise restrictions on the ramp.