WIth forecasts of an increase in sunspots and solar flares in the coming months, pilots are being cautioned about a corresponding increase in the sun’s contribution to cosmic radiation, which some aeromedical specialists believe may be associated with skin cancers and breast cancer in crewmembers whose flights typically are conducted at higher altitudes.
The International Federation of Air Line Pilots’ Associations (IFALPA) approved a policy in late 2012 calling for some aircraft that operate above 26,000 ft in polar and sub-polar regions to be equipped with warning devices to inform pilots of sudden increases in the rate of radiation exposure.
The policy also said that flight personnel who receive an effective dose of more than 1 millisievert (mSv) of radiation per year (the equivalent of 100 tooth X-rays; Table 1, p. 34) “should be recognized as occupationally exposed to ionizing radiation. Those who are liable to receive an effective dose greater than 6 mSv per year should be [classified as among those exposed to the highest doses].”
In addition, IFALPA recommended that a task force sponsored by the International Civil Aviation Organization (ICAO) be established to address issues associated with any ionizing radiation event “and the possible subsequent emergency descent of a large number of aircraft.”
“Radiation has been, and will be, affecting pilots always,” IFALPA added. “It is one occupational risk factor among others, but fortunately the risk for health effects, with our current knowledge, is very low.”1
Numerous studies of crewmembers’ cancer risks have concluded that, although the overall cancer risk is not elevated, the risks are higher for malignant melanoma and other skin cancers, as well as breast cancer for female crewmembers, IFALPA said.
Summarizing the findings of more than 65 studies in the past 20 years, IFALPA added that some studies also showed a higher risk of brain cancer.
“Overall, aircrew are a highly selected group with many specific characteristics and exposures that might also influence cancers or other health outcomes,” IFALPA said. “Radiation-associated health effects have not been clearly established in the studies available so far. However, it is certainly worth noting that whilst the annual exposure of other radiation workers (e.g., nuclear workers, medical and industrial radiographers) is decreasing following the introduction of the principle to reduce doses as low as reasonably achievable, radiation doses of airline flight crew do continue to increase, as advances in aerospace technology permit longer duration, higher altitude and higher latitude flights.”
U.S. Federal Aviation Administration (FAA) aeromedical researchers said in a 2003 report that the primary concern for crewmembers (and unborn children who are exposed to cosmic radiation during their mothers’ pregnancies) is a “small increase in the lifetime risk of fatal cancer” and a risk of genetic defects for future generations.2
Earth and everything on it are constantly subjected to cosmic radiation, which originates both in deep space — known as background cosmic radiation or galactic cosmic radiation — and in the sun — called solar radiation.
Solar radiation, which is generated when disturbances on the sun’s surface release high-energy solar protons, increases in intensity as solar flare activity increases, which it does in cycles that vary in length but typically last between nine and 14 years.
The current cycle, which began in 2008, is expected to last 11 years, with the so-called solar maximum — the period when sunspots and solar flares are most frequent — likely to occur later in 2013, according to experts in solar weather forecasting, including the U.S. National Aeronautics and Space Administration (NASA).3 The solar storms that occur, especially during the solar maximum, can lead to short-term increases in radiation levels — increases that can prompt airlines to reroute some flights, primarily to avoid a radiation increase that could place crewmembers at risk of exceeding the maximum recommended exposure and could interfere with high frequency (HF) radio transmissions.
The flights that most frequently are subject to rerouting are those at higher altitudes and higher latitudes — in polar areas — where cosmic radiation levels are relatively high. This is because at high altitudes, there is less air above an airplane to shield it from radiation, and in polar areas, Earth’s magnetic field offers less protection against radiation.
A large-scale rerouting occurred in February 2011, forcing airlines to re-book passengers and pay increased fuel costs related to the longer routes that took the place of the planned polar flight paths.
IFALPA says that five solar storms in the past 60 years have had radiation levels so high that individuals on a single trans-Atlantic flight would have exceeded the recommended 1 mSv annual radiation limit for members of the public. For crewmembers, a trans-Atlantic flight during one of those severe solar storms would have provided exposure to the same amount of radiation received during three months of typical airline flying.
Several computer programs have been developed to provide estimates of the radiation exposure on a given flight. For example, the European Program Package for the Calculation of Aviation Route Doses (EPCARD) calculates radiation exposure by taking into account the departure airport, duration of climb, flight altitude, duration of descent, destination airport and number of flight levels.4
The CARI-6 computer program, developed by the FAA Civil Aerospace Medical Institute (CAMI), works in a similar fashion, calculating radiation exposure by considering the shortest route between any two airports. The FAA says the program also takes into account the date of the flight to determine changes in Earth’s magnetic field and current solar activity that may affect levels of cosmic radiation penetrating the atmosphere. The program also calculates the dose rate at any geographic location or altitude up to 60,000 ft.5
PCAire says it laid the groundwork for its web-based program by having its researchers carry “a large radiation detector, sensitive to cosmic rays, on hundreds of flights. The radiation field was recorded every minute along each of these flights. Analysis of this data led to the development of mathematical functions that matched the measurements for any flight, at any altitude and anywhere in the world. The PCAire code uses these mathematical functions to calculate the dose to a person on a given flight. For each flight that is entered, the code takes into account the date, time and flight path and recomputes the radiation field during that flight.”6
In the United States, a solar radiation alert system continuously analyzes satellite measurements of high-energy solar protons to determine whether the effective dose rates are elevated at aircraft flight altitudes.
If a substantial elevation is detected, an alert is issued by the CAMI via the National Oceanic and Atmospheric Administration (NOAA) and a global network of agency counterparts. The alert includes an estimate of radiation levels at altitudes from 20,000 ft to 80,000 ft at specified latitudes, and a recommended maximum flight altitude at those latitudes. For air carriers, the recommended response to a solar radiation alert is to “minimize flight time at altitudes that exceed the recommended maximum flight altitude,” the CAMI report said.7
As noted earlier, when scientists have determined that elevated dose rates are expected, airlines have re-routed polar flights to avoid exposure to increased cosmic radiation — and to avoid the possibility of interference with HF radios. When the large-scale reroutings occurred in 2011, airline flights from the United States to Asia were forced to detour south over Alaska (ASW, 11/11).
Chris Mertens, senior scientist at the NASA Langley Research Center in Hampton, Virginia, said, however, that the current system does not monitor aviation occupational radiation exposure.8
A report quoted Mertens as saying that the average commercial airline pilot receives “more radiation exposure than a fuel-cycle worker in a nuclear power plant.”
Mertens said he and other NASA scientists are working with NOAA and the National Institute of Occupational Safety and Health to better understand the effects of radiation on aircraft crewmembers and incorporate radiation predictions into National Weather Service forecasts.
IFALPA identified two methods of providing in-flight protection against cosmic radiation — radiation shielding or imposing limits on exposure.
“It is impractical to shield aircraft effectively from cosmic radiation,” IFALPA said. “Therefore, the most viable option for flight crew is dose constraints/limits.”
The International Commission on Radiological Protection (ICRP), an independent, non-government organization that provides guidance on protection against the radiation risks, says — and most civil aviation authorities agree — that the recommended effective dose limit for airplane crewmembers is 20 mSv per year, averaged over five-year periods, or 100 mSv per five years, and that exposure in any one year should not exceed 50 mSv.
Accompanying ICRP recommendations are that pregnant crewmembers should not be exposed to more than 1 mSv “from declaration of pregnancy for the remainder of the pregnancy” and that passengers should be exposed to no more than 1 mSv per year.
In the United States, the FAA has no binding radiation-related regulations but recommends that operators comply with the ICRP’s recommended limitations, including the annual dose limit of 20 mSv.
In Europe, many individual nations have stricter limits; typically, they set a 6 mSv limit on the allowable dose from occupational exposure to cosmic radiation, IFALPA said.
ICAO requires that all airplanes that are intended to be operated above 49,000 ft carry equipment “to measure and indicate continuously the dose rate of total cosmic radiation being received … and the cumulative dose on each flight.”9
Other requirements call for the equipment’s display unit to be visible to a flight crewmember and for the operator to maintain records of the relevant flights “so that the total cosmic radiation dose received by each crewmember over a period of 12 consecutive months can be determined.”
- IFALPA. Medical Briefing Leaflet: Cosmic Radiation. Nov. 2, 2012.
- Friedberg, Wallace; Copeland, Kyle. Report DOT/FAA/AM-03/16, What Aircrews Should Know About Their Occupational Exposure to Ionizing Radiation. FAA Civil Aerospace Medical Institute. October 2003.
- NASA Marshall Space Flight Center. Solar Cycle Prediction. Feb. 1, 2013. solarscience.msfc.nasa.gov/predict.shtml.
- EPCARD is available at www.helmholtz-muenchen.de/epcard/eng_fluginput.php.
- FAA. CARI-6: Radiobiology Research Team. www.faa.gov/data_research/research/med_humanfacs/aeromedical/radiobiology/cari6/.
- The PCAire program is available at pcaire.com.
- Friedberg, Copeland.
- Finneran, Michael. Earth and Sun: Thousand-Fold Rise in Polar Flights Hikes Radiation Risk. Feb. 18, 2011.
- ICAO. Annex 6 — Operation of Aircraft.