Scientists at NASA's Langley Research Center have completed a first attempt to accurately calculate the level of damaging radiation flight crews and passengers are exposed to on commercial airline flights. The work is an early step toward developing a model to observe radiation exposure for all commercial flights, particularly for pilots and crews who spend their careers airborne and who are at greater risk of developing certain cancers.
The study considered not only everyday radiation emanating from space, but also the additional energy unleashed during a solar storm, which can be profound. NASA scientists say not including geomagnetic effects on solar radiation in modeling radiation exposure could underestimate the dosage by 30 to 300 percent.
Researchers looked at passengers and crew on typical flights from Chicago to Beijing, Chicago to Stockholm and London to New York, during what is known as the Halloween 2003 Storm. These flights were chosen because of their long flight paths near the North Pole, where the Earth's natural protection from radiation is weakest. Earth's magnetic field approaches zero above the poles. The Halloween 2003 event was chosen because it was both a large and a complex storm, making it a good test for the model.
The study found that aircrew and passengers during the Chicago to Beijing flight, for example, would have been exposed to about 12 percent of the annual radiation limit recommended by the International Committee on Radiological Protection. But these exposures were greater than on typical flights at lower latitudes, and confirmed the concerns about commercial flights at high latitudes.
"The upshot is that these international flights were right there at that boundary where many of these events can take place, where radiation exposure can be much higher," said Chris Mertens, senior research scientist at NASA's Langley Research Center, who is leading the research effort. Mertens will present his latest results at the American Geophysical Union fall meeting in San Francisco on Dec. 16.
Piecing together the radiation exposure on these typical flights is the first step toward developing a real-time system that researchers hope will become a standard component of commercial airline cockpits. Radiation exposure could one day be taken into account in the same way weather conditions are considered before deciding to fly or deciding what exact route to fly and at what altitude.
Flying above and beyond Earth's natural protection
The number of international flights that skirt the north pole are increasing. Airlines save massive amounts of fuel on flights such as Chicago-to-Shanghai by simply flying "over the top" – it is a far shorter route than following the latitude lines. But while saving fuel, these flight paths take planes and their passengers to the thinner layers of Earth's magnetosphere, which shields potentially harmful solar and cosmic radiation.
On a typical day, the Sun is quiet and "background radiation," the cumulative effect of radiation from cosmic sources reaching Earth, is the only other source. But when the Sun is not quiet, violent storms on the star's surface eject powerful bursts of radiation to the Earth. It is these events that have never been truly accounted for in studies of how much radiation pilots and airline passengers are exposed to.
Pilots Await Results
While the flights studied appear to have not put passengers in danger of exceeding the safe radiation limit in an individual flight, concerns remain, Mertens said. Many workers whose jobs expose them to consistent radiation sources log that exposure to keep a record over one's career. People who work on commercial airline flights are technically listed as "radiation workers" by the federal government – a classification that includes nuclear plant workers and X-ray technicians. But unlike some others in that category, flight crews do not quantify the radiation they are exposed to.
Mike Holland, an American Airlines captain and vice chairman for radiation and environmental issues with the Allied Pilots Association, said he is following Mertens' research with interest. The pilots association has written a formal letter in support of the research. Holland cited studies that show pilots face a four-times greater risk of melanoma than the general population. But because pilots and flight crews do not wear radiation-measuring badges like other radiation workers, the only estimates about their career-long exposure come from models.
Up until now, most of those models only attempted to capture the amount of cosmic background radiation that reaches airliners in flight. Holland said he believes including solar radiation, especially during solar storms, is important. He looks forward to having answers for the pilots who contact him with questions about radiation and cancer risk.
"When I talk to epidemiologists, they have two questions for me: What is your exposure? And what is your health for 20 to 30 years after you retire?" Holland said. The second question he and other pilots can answer, in time. But as of now, they can't measure their exposure.
"We're excited that Chris is doing this," Holland said, "and we hope it can answer the epidemiologists first question, which is, 'What is your exposure?'"
NASA's Langley Research Center