What happened
On the evening of December 10, 2015, an Eurowings Bombardier CRJ 900, registration D-ACNP, was operating a scheduled flight from Geneva (LSGG) to Düsseldorf (EDDL). During taxiing at Geneva, the co-pilot noticed an unusual odor in the cockpit. Believing the smell to be a common operational occurrence, the crew proceeded with the departure.
As the aircraft climbed through French airspace, the odor became noticeable to the cabin crew as well. The co-lagging effects of the smell became severe enough that the pilot donned an oxygen mask, experiencing symptoms including headaches, dizziness, and difficulty concentrating. The cabin crew also reported physical sensations, specifically tingling in the lips and a furry sensation on the tongue.
After reaching flight level 280, the crew declared a Pan Pan urgency and initiated a descent and return to Geneva. The aircraft landed at Geneva at 20:38 UTC, where emergency services were waiting. The crew described the odor as a possible oil smell, which remained detectable in the cockpit even after the aircraft had parked.
The investigation
Investigators examined the aircraft's environmental control system (ECS) and the air conditioning packs. During a ground run in Geneva the following day, an unusual odor was detected near the right air conditioning pack, and an "internal fault" message appeared on the air conditioning system controller.
Subsequent technical inspections in Düsseldorf focused on the air conditioning ducting, engine oil consumption, and the auxiliary power unit. While no external oil leaks were found on the engines or the flow control valve, investigators discovered that both recirculation fan filter cartridges were heavily contaminated with dust.
Findings
- The heavy contamination of the air conditioning filter cartridges was the likely source of the odor.
- It is probable that the reduced airflow caused by the clogged filters led to the overheating of the recirculation fan bearings, which released the irritating smell into the cabin and cockpit.
- The aircraft's maintenance diagnostic computer did not record a "recirc fan fault" message, and the thermal switches on the fan motors failed to automatically shut down the fans despite the overheating.
- The crew's decision to divert the flight and return to Geneva was a safety-conscious action.
Safety action
- The investigation noted that while the captain did not feel personally impaired, the co-pilot's decision not to use an oxygen mask despite experiencing symptoms was difficult to justify. The report emphasizes that when dealing with potentially toxic substances, protective measures should not be bypassed while waiting for symptoms to manifest.