The FAA’s updated Advisory Circular AC 120-61B provides information to help air carriers augment–but not alter or amend–existing programs to inform crew members about radiation exposure. The AC explains the differences between the natural sources of radiation in the atmosphere as well as the average annual exposure a human experiences from those sources.
“In aviation, the principal source of exposure is galactic cosmic radiation, which is fairly constant in nature,” the new AC states. “Sources of less consistent importance include solar cosmic radiation, shipments of radioactive materials, clouds of radioactive gas, and terrestrial gamma-ray flashes, which are on rare occasions associated with lightning.”
More specifically, when galactic cosmic radiation is encountered, less radiation will be received on a lower-latitude flight because of the greater amount of radiation shielding provided by the earth’s magnetic field. This shielding is greatest near the equator and gradually decreases to zero closer to the poles, where galactic cosmic radiation levels are about double those at the equator.
The Solar Radiation Alert System, which is broadcast on the National Oceanic and Atmospheric Administration (NOAA) wire service and has been developed by the FAA’s Civil Aerospace Medical Institute, uses data provided by NOAA’s Space Weather Prediction Center. It alerts users of the beginning of a disturbance on the sun that can lead to high doses of ionizing radiation in the earth’s atmosphere. Responding to an alert by flying at a lower altitude can significantly reduce radiation exposure in high-latitude areas of concern.