A team of German scientists has identified toxins in the bodies of aircraft crew members who believe they've experienced a "fume event" - a technical glitch where toxins from the engine contaminate cabin air.
Headaches, vomiting. Feeling irritated or a tingling sensation in arms and legs. Feeling drowsy. Being unable to focus. It's a long list of symptoms patients describe when they come see Professor Astrid Heutelbeck and her team at the University of Göttingen.
For the past two years, they have analyzed postflight blood and urine samples of more than 140 patients - most of them crew members - and in most of these samples they found traces of toxins.
These so-called volatile organic compounds don't stay in the body for too long and are only detectable for a short period of time. However, Heutelbeck told DW there is reason to believe that the more people are exposed to these substances, the more harm they could do in the body due to "additive effects".
Such incidents, usually referred to as "fume events," happen when there is a technical glitch in the aircraft that allows toxins from substances like kerosene, oils and antifreeze to leak into what is known as "bleed air" - air from turbine engines that finds its way into the cabin.
"We also took blood and urine samples [from passengers who have been on] flights without incidents and can say there were no traces of pollution of this kind," Heutelbeck said.
The danger of fume events made headlines several years ago, when it became known that a pilot and his co-pilot barely managed to avert a crash when they both felt sick all of the sudden and had trouble steering the plane.
"This study is really a big step forward," said Christoph Drescher, a flight attendant and the General Secretary of the European Cabin Crew Association (EurECCA), which represents nine crew member unions. "It's the first time, European-wide, that this study has found evidence that there is a connection between fume events and the sickness of cabin crew," he said.
"It's certainly a big issue for us," Drescher said. "Fume events occur quite regularly."
According to statistics by the Federal Office of Civil Aeronautics, 44 such events were registered last year. But many incidents go unreported, Drescher said.
The union has called for filters and sensors and the development of neurotoxically harmless oils. And there has been some progress when it comes to dealing with fume events, Drescher said.
"We see a little bit of change," Drescher said. "Two, three years ago, there was the general notion of 'This problem does not exist.'
"Now, airline operators like Lufthansa or other German airlines say 'Ok we do have a case here - what do we do?'"
So far, he said, there is only one type of passenger aircraft, the Boeing 787 Dreamliner, that doesn't use the system of bleed air, but draws fresh cabin air from a separate source away from the engines.
Filter technologies and other solutions
Airlines like Lufthansa are aware of the potential danger of fume events. "We've developed a measuring kit as the world's first and only airline that can detect several hundred substances," Lufthansa Group's spokesperson Andreas Bartels told DW. "Samples measuring air quality did not exceed critical values at any point in time."
At the same time, the airline was also pushing for filter technologies and teamed up with manufacturers Airbus and Rolls-Royce to work on new types of engines.
"We are taking the issue of fume events very seriously at Lufthansa," Bartels said. The company's analysis had already led to changes in one of the engines of the A380, he added.
At least in Germany, manufacturers, airlines and unions have joined forces to come up with solutions to the fume issues, EurECCA's Drescher said. The unions also push for regulations to have illnesses linked to fume events recognized as occupational accidents. "That's not the case now. You are totally on your own if you can't work anymore," Drescher said.
According to Heutelbeck, the duration of patients' symptoms varies. For some, it might be gone as quickly as it came, but others suffer for weeks or months, she said.
"In the long run, we'd like to see a change in the manufacturing of an aircraft," Drescher said. But this will take time - and doesn't come cheap.