Fumes entering the flightdeck of a Boeing 737-700 caused the co-pilot to be overcome by nausea, according to an incident report produced by German air accident investigation agency BFU.
In addition, blood taken from the co-pilot immediately after the flight on 18 November 2011 tested positive for the neurotoxin tri-ortho-cresyl phosphate (TOCP), said the report. The BFU is now further investigating the medical implications of the exposure to the chemical.
According to the BFU incident bulletin, Air Berlin flight 8407 from Milan Malpensa to Düsseldorf suffered a cockpit fume event - described as "a strong smell" - shortly after take-off. A few minutes later the co-pilot was overcome by nausea and had to leave the flightdeck for the washroom. The flight was operated by Germania for Air Berlin using a Boeing 737-700 (D-AGEU).
Having recovered sufficiently to return, the co-pilot immediately went on oxygen for about 15min and then felt well enough to remove the mask. Meanwhile, the captain continued the flight toward Düsseldorf unaided.
The report said that passing 7,000ft in the descent the smell returned, although only the co-pilot noticed it, and he again donned the oxygen mask. The captain landed the aircraft safely at Düsseldorf.
A blood sample was taken from the co-pilot at a local hospital. The blood was sent for further testing by specialists at the University of Nebraska, which sent the following report to the BFU: "[The blood] is positive for exposure to tri-ortho-cresyl phosphate. This sample had a strong signal for the adduct on butyrylcholinesterase. It was estimated that 1.4% of [the co-pilot's] butyrylcholinesterase was modified as a consequence of exposure to TOCP."
Butyrylcholinesterase is a naturally occurring bodily enzyme with several neurological functions related to muscle activity and cognition, and the co-pilot's butyrylcholinesterase, as the University of Nebraska test report stated, had been "modified" by the presence of TOCP.
The BFU report said that further medical assessment of the effect of TOCP on health is being conducted as a result of this event.
Air Berlin issued a statement from the aircraft's operator, Germania, on the event: "The safety of Germania passengers and crew members is always top priority. For them there was never a threat; the safe conduct of the flight was always guaranteed. Germania takes the incident very seriously. We have immediately reported the incident to the federal aviation authority and fully support its investigations.
"Our reputation depends not only on ensuring flight safety but also on the welfare of the crew members and passengers. In no other area is the issue of safety as strictly regulated and monitored as in aviation."