What happened
On January 2, 2015, an Airbus A321 operating a flight from Frankfurt Main to Hamburg experienced an unusual odor event during the climb phase. The flight attendants first reported a sharp, unpleasant smell, described as resembling burnt dust, throughout the cabin. The captain initially attributed the odor to the aircraft's long ground time and high humidity.
As the aircraft approached Hamburg and entered cloud cover, the intensity of the odor increased significantly. The crew described the smell as becoming "biting" and pungent. In an attempt to mitigate the issue, the captain switched the bleed air configuration to isolate the number one engine bleed, but the odor persisted. Due to the intensifying smell, the pilots decided to don oxygen masks at approximately 08:25 local time.
Despite the use of masks, the crew reported physical symptoms, including tingling in the fingers and lightheadedness. The pilot informed air traffic control that the crew was wearing oxygen masks and that communication might be affected by the equipment. The aircraft landed safely at Hamburg at 08:31 local time, accompanied by the fire department to the gate.
The investigation
The BFU examined the aircraft's technical records, flight data, and cockpit voice recordings. Maintenance logs showed that no leaks or contamination were found in the engines or the Auxiliary Power Unit (APU) during subsequent inspections. Air quality testing was performed using an Aerotracer device during an engine run-up; while no engine oil was detected, the tests identified traces of glycol, acetone, and ammonia.
Investigators also reviewed the physical symptoms reported by the crew. While the captain experienced tingling and dizziness, the co-pilot reported that his symptoms vanished once the oxygen masks were applied. The investigation could not definitively identify a specific chemical source or confirm that the concentration of volatile organic compounds (VOCs) was high enough to pose a significant accident risk.
Findings
- An unidentified odor event occurred during the flight, leading the crew to use oxygen masks.
- The Airbus A321 crew remained capable of performing all necessary flight duties, and the landing was conducted stably.
- The exact source of the odor and the specific contaminants responsible for the crew's symptoms could not be determined.
- There was no evidence of a high probability of an accident, as the crew's ability to control the aircraft was not significantly impaired.
- No technical defects or leaks were found in the engines or the environmental control system during post-flight inspections.