A trip on a jet plane is often taken in a party-like atmosphere with passengers confident that, barring any unexpected accidents, they will return to earth safely and with no lasting physical affects. But depending on what the sun is doing, a solar storm can produce enough radiation to equal a significant fraction of a chest X-ray's dosage even at typical passenger altitudes of 35,000 feet. The situation is even worse for airline pilots and flight attendants who spend over 900 hours in the air every year. According to a report by the Department of Transportation ( Science News magazine, vol. 137, p. 118), the highest dosages occur on international flights passing close to the poles where the earth's magnetic field concentrates the dosages. The annual federally recommended limit for pregnant women is 500 millirems. Even at these levels, there will be on the average four extra cases of mental retardation per 100,000 women due to this exposure between weeks 8 to 15 in the gestation cycle.
Although the dosage you receive on a single such flight per year is very small, frequent fliers who amass over 480 hours of flight per year would statistically expect to suffer from 500 extra cancer deaths per 100,000 travelers over a 20 year period. Airline crews who spend 900 hours in the air on such polar routes would have over 1000 additional cancer deaths per 100,000 crew members over a 20 year period of travel. By comparison, the typical cancer rate is about 22,000 deaths per 100,000. This means that instead of a 22 in 100 chance of cancer, airline crews and frequent fliers would have as much as a 23 in 100 chance of cancer death. This doesn't sound like much, but for a population as large as the United States with nearly 300 million people, this means an additional 3 million people would die if they all traveled on such routes. of course only a small number of people are this well-traveled, but nevertheless, without proper safeguards, hundreds of additional people would die from such radiation exposure.
Matthew H. Finucane, air safety and health director of the Association of Flight Attendants in Washington DC, is quoted in Science News ( vol. 137, p. 118) advocates asking the FAA to monitor and regulate radiation exposure and, if possible, to warn crews of unusually intense bursts of cosmic radiation, or solar storm activity. Currently, the FAA guidelines are written in too technical a language to be readily useful to pilots and flight attendants so that they need to be re-written.