What happened
On 23 September 2019, an Airbus A320-232, registration G-EUYB, was performing a commercial passenger flight from Zurich to London Heathrow. During the initial climb, the crew detected a faint, unpleasant odour, which they initially dismissed after it temporarily dissipated. However, as the aircraft descended through 4,000 ft, a sudden and intense smell, described by the commander as resembling manure, filled the flight deck. The co-pilot reported physical symptoms, including itchy skin and a scratchy throat.
In response to the sudden onset of fumes, the commander instructed the co-pilot to don an oxygen mask. The crew declared a PAN to Heathrow Tower and requested a priority landing. The aircraft landed safely on Runway 27L and stopped on a taxiway. Once stationary, the co-pilot removed his mask to check for the continued presence of the odour, at which point he became nauseated and vomited. The commander also felt unwell. Both pilots were subsequently transported to a hospital for medical assessment and were released later that day.
The investigation
The AAIB investigation focused on identifying the source of the transient fumes. Investigators examined the aircraft's flight data, cockpit voice recorder, and the digital ACMS recorder, finding no anomalies in the engine pneumatic bleed or air conditioning systems. Maintenance inspections, including access to the avionics bays and various system tests using the APU and engines, failed to detect any residual odours or chemical traces.
Further review of the operator's records revealed a pattern of similar, unidentified fume events within their fleet. The investigation also considered environmental factors, noting that many such incidents occurred following periods of precipitation or high humidity. While the exact chemical composition of the fumes could not be sampled due to their rapid dissipation, the investigation explored the possibility of contaminants entering the Environmental Control System (ECS) from the engines or APU.
Findings
- The source of the fumes in G-EUYB could not be definitively identified.
- The fumes were transient and left no detectable physical residue or traces in the cockpit after the event.
- The presence of high humidity or recent precipitation may contribute to the release of contaminants into the ECS.
- The co-pilot suffered minor injuries in the form of physiological distress and nausea leading to incapacitation.
- The crew's adherence to smoke and fumes checklists and the use of oxygen masks prevented further injury and ensured a safe landing.