What happened
The Icelandic Transportation Safety Board (RNSA) initiated a multi-year investigation following numerous reports of flight crew members experiencing illnesses during flight. The investigation specifically focused on incidents involving Boeing 757 and Boeing 767 aircraft operated by an Icelandic carrier. These incidents involved crew members experiencing acute symptoms during flight, with some suffering from long-term health issues following the exposures.
To establish a broader context, the RNSA reviewed 216 similar reported incidents involving crew illnesses across all operators and aircraft types between 201 and 2020. The data showed that these incidents were widely distributed across various flight routes and were not concentrated in specific geographic locations. However, a pattern was observed regarding flight timing, with the highest frequency of incidents occurring during morning flights from Iceland to Europe and evening/night flights from North America to Iceland.
The investigation
The RNSA examined eight specific cases involving Boeing 757 and Boeing 767 aircraft occurring between 2016 and 2019. The investigation sought to determine if environmental factors within the cabin were responsible for the reported illnesses. In some instances, the RNSA was able to conduct on-site inspections immediately upon landing while the aircraft were still in flight.
Surface samples were taken from the cabin of both a B757 and a B767. The analysis revealed the presence of Tri-Cresyl-Phosphate (TCP) compounds on cabin surfaces, particularly near the air vents. The investigation noted that cabin air is supplied via bleed air from the engines. While the B767 fleet's engine oil contains 1-3% TCP, the operator's policy for the B757 fleet generally mandates the use of oil without TCP. However, the investigation found that TCP was present in the oil used in at least one B767 engine and that the operator's maintenance protocols allow for the use of alternative oils if the primary type is unavailable, meaning TCP could potentially enter the B757 fleet.
Furthermore, the investigation found that the accumulated service time of bearings and seals near the bleed air intakes—some of which had been in service for up to 28 years—was not specifically tracked in the operator's maintenance system. There was also evidence that contaminated components, such as engines, could potentially spread contamination between aircraft during maintenance transfers.
Findings
- The presence of TCP compounds in the passenger and crew compartments may be attributable to engine oil entering the cabin through engine bleed air.
- The potential introduction of TCP via engine bleed air is a primary suspected cause of the chemical presence.
- Other potential sources of TCP include the Auxiliary Power Unit (APU) or the airport environment, though these could not be definitively confirmed as the sole source.
- The investigation could not determine if the exposure resulted from a single event or a long-term accumulation of the chemical.
- A lack of specific tracking for the service life of engine components near air intakes contributed to the difficulty in assessing long-term contamination risks.
Safety action
Following these incidents, the operator has implemented various corrective measures and has been working toward a systematic renewal of its aircraft fleet. Since 2021, the number of reported similar incidents has decreased significantly, with only 14 reported cases between 2021 and the first nine months of 2024.