Advisory 

Circular

Subject: In-flight Radiation Exposure Date: 7/6/06 AC No: 120-61A 

Initiated by: 

AFS-210/AAM-600 

1. PURPOSE. This advisory circular (AC) provides: 

a. Information intended to augment (not alter or amend) existing programs an air carrier may 

be using to inform crewmembers about radiation exposure; and 

b. Links to sources of information regarding in-flight radiation exposure. 

2. CANCELLATION. This AC cancels: 

a. AC 120-52, Radiation Exposure of Air Carrier Crewmembers, dated March 5, 1990. 

b. AC 120-61, Crewmember Training on In-flight Radiation Exposure, dated May 19, 1994. 

3. DEFINITIONS. 

a. Conceptus. Any stage of prenatal development from fertilized egg to birth. 

b. Galactic Cosmic Radiation. The ionizing radiation that originates outside the solar 

system, a main source of which is thought to be exploding stars (supernovae). 

c. Ionizing Radiation. Refers to subatomic particles of matter (e.g., neutrons, protons, and 

electrons) and massless particles of energy (X-rays and gamma rays), with each particle having 

sufficient energy so that, on interacting with a material, it can cause an atom to lose an orbital 

electron. Low levels of ionizing radiation are a normal part of our environment. Substances that 

emit ionizing radiation are present in every cell in the body. 

d. Solar Particle Event. An increase in ionizing radiation from the sun. Particles of 

ionizing radiation from the sun that reach the earth’s atmosphere come from all directions 

because of the spreading effect caused by the interplanetary and earth’s magnetic fields. 

e. Solar Radiation. A severe disturbance in the sun that leads to a large flux of fastmoving, subatomic, ionizing-radiation particles (often called solar cosmic radiation) that 

penetrate the earth’s magnetic field and enter the atmosphere. The particles interact with air 
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atoms in the same way as galactic cosmic radiation. A consequence is that, for varying lengths 

of time, ranging from a few minutes to more than a day, air travelers may be exposed to ionizing 

radiation from the sun as well as galactic cosmic radiation. 

4. RELATED READING MATERIALS. The following reading materials are useful as 

further guidance and in developing training program subject material. For information on how to 

obtain these materials, see paragraph 11a. 

a. “Radiation Protection Guidance to Federal Agencies for Occupational Exposure,” Federal 

Register 52 (17): pp. 2,822-2,834 (January 1987). 

• Unlawful employment practice for an employer, footnote to p. 2,829 

• Recommendations regarding occupational exposure to radiation, section 7 on p. 2,832 

b. National Council on Radiation Protection and Measurements, “Exposure of the 

Population in the United States and Canada from Natural Background Radiation.” NCRP Report 

No. 94. Bethesda, MD, 1987. 

c. Friedberg W, Copeland K, Duke FE, Nicholas JS, Darden Jr. EB, O’Brien III K, 

“Radiation Exposure of Aircrews,” Occupational Medicine: State of the Art Reviews 17(2): 

293-309, 2002. 

• Galactic cosmic radiation in the atmosphere as related to altitude and latitude, 

pp. 294-298 

• Effective dose of galactic cosmic radiation to the mother is a reliable estimate of the 

equivalent dose to the conceptus, p. 299 

• Ionizing radiation from the sun, p. 299 

• Recommended radiation exposure limits, p. 300 

• Health concerns regarding radiation exposure, p. 300 

• Risk of fatal cancer for a working-age population, p. 301 

• Deaths in the general population from cancer: adults; p. 301; all ages, p. 303 

• Risks from irradiation in utero, p. 302 

• Inherited genetic defects from parental irradiation, p. 307 

• Abnormalities at birth in the general population, p. 307 

d. Hall, EJ, “Radiobiology for the Radiologist.” Fifth Edition 2000, Lippincott Williams & 

Wilkins, Philadelphia, PA. 

• Equivalent dose and effective dose defined, pp. 236-237 

e. Bagshaw, Michael, “Cosmic Radiation in Commercial Aviation,” International Academy 

of Aviation and Space Medicine, June 2004. 

5. SOURCES OF EXPOSURE. The average annual doses of ionizing radiation a person in the 

United States typically receives from natural sources are set forth below: 
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Source Effective dose, millisieverts 

 (% of total) 

Galactic Cosmic Radiation * 

(Uniform whole-body exposure) 0.27 (9%) 

Inhaled Radon 

(Primarily to bronchial epithelium) 2.0 (68%) 

Radioactive Material in the Ground 

(Uniform whole-body exposure) 0.28 (9%) 

Radioactive Material in Body Tissues 

(Tissue doses vary) 0.40 (14%) 

 Total from natural sources = 2.95 (100%) 

* Includes 0.01 millisievert from air travel. 

6. EXPOSURE VARIABLES. Radiation received on a lower-latitude flight will be lower 

because of the greater amount of radiation shielding provided by the earth’s magnetic field. This 

shielding is maximum near the equator and gradually decreases to zero as one goes north or 

south. Radiation levels over the polar regions are about twice those over the equator at the same 

altitudes. A map of high-latitude areas of concern is available on the following FAA Web site: 

http://www.faa.gov/education_research/research/med_humanfacs/aeromedical/radiobiology/solar

radiation/index.cfm. 

a. A solar radiation alert system developed by the FAA’s Civil Aerospace Medical Institute, 

with data provided by the Space Environment Services Center of the National Oceanic and 

Atmospheric Administration (NOAA), alerts users of the beginning of a disturbance on the sun 

that can lead to high-dose rates of ionizing radiation in the earth’s atmosphere. Solar radiation 

alerts are transmitted worldwide to subscribers of NOAA’s Weather Wire Service. A message is 

transmitted at the beginning and end of an alert. A test message is transmitted daily. 

Responding to an alert by flying at a lower altitude can significantly reduce radiation exposure in 

high-latitude areas of concern. 

b. A description of the methodology associated with the solar radiation alert system can be 

found by linking to the technical report entitled “Solar Radiation Alert System” (DOT/FAA/AM05/14), available on the following FAA Web site at: 

http://www.faa.gov/library/reports/medical/oamtechreports/2000s/media/0514.pdf. 

7. RECOMMENDED LIMITS. 

a. When considering the harmful health effects of postnatal (child or adult) exposure to 

ionizing radiation, the current practice is to express the amount of radiation received in terms of 

effective dose. If the radiation exposure is to a conceptus (any stage of prenatal development 

from fertilized egg to birth), dose is expressed in terms of equivalent dose. The unit of both 

effective dose and equivalent dose is the sievert, which is a measure of the biological harm that 

ionizing radiation may cause: 1 sievert = 1000 millisieverts.
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b. The recommended occupational exposure limit for ionizing radiation is a 5-year average 

effective dose of 20 millisieverts per year, with no more than 50 millisieverts in a single year. 

For a pregnant crewmember, the recommended limit for the conceptus is an equivalent dose of 

1 millisievert, with no more than 0.5 millisievert in any month.

c. The FAA has linked to its Web site the following two technical reports regarding radiation 

exposure during pregnancy: 

(1) “In-flight Radiation Exposure During Pregnancy” (published by the American 

College of Obstetricians and Gynecologists), at: 

(http://www.acog.org/from_home/publications/green_journal/2004/v103n6p1326.pdf). 

(2) “Galactic Cosmic Radiation Exposure of Pregnant Aircrew Members II” (FAA 

technical report DOT/FAA/AM-00/33), at: 

(http://www.faa.gov/library/reports/medical/oamtechreports/2000s/media/00_33.pdf). 

8. RISK ASSOCIATED WITH EXPOSURE. The probability of a radiation-caused cancer or 

genetic defect is related to the total amount of radiation accumulated by an individual. Based on 

current scientific thinking, any exposure to radiation can be harmful and increase the risk of 

cancer. At very low exposures, however, the estimated increases in risk are very small. 

a. Individuals exposed to excessive levels of ionizing radiation are at increased risk for 

cancers and are at risk of passing on genetic defects to future generations. Ionizing radiation can 

cause changes in the chemical balance of cells, which can cause cell damage or cell death. In 

some cases, there may be no effect. In other cases, the cell may survive but become abnormal, 

either temporarily or permanently. An abnormal cell may become malignant. 

b. The likelihood of developing cancer because of occupational exposure to galactic cosmic 

radiation is a small addition to health risks experienced by the general population. Currently, it 

is not possible to establish that an abnormality or disease in a particular individual resulted from 

exposure to galactic cosmic radiation at the doses likely to be received while flying. 

9. MANAGING EXPOSURE. 

a. How to Calculate Exposure. The FAA has computer programs available on its Web site, 

called CARI-6 and CARI-6M. These programs can be used to estimate the effective dose of 

galactic cosmic radiation. No programs are currently available for use in estimating the effective 

dose received from a solar particle event. The dose of ionizing radiation that an individual might 

receive during a solar particle event cannot be estimated in advance. Research is currently being 

conducted on how best to estimate flight doses on the basis of satellite and ground-level 

measurements made during an event. 

(1) CARI-6. This program calculates the effective dose of galactic cosmic radiation 

received by an individual (adult) on an aircraft flying a great-circle route between any two 

airports in the world. The program takes into account changes in altitude and geographic 
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location during the course of a flight, as derived from the flight profile entered by the user. 

Based on the date of the flight, appropriate databases are used to account for effects of changes 

in the earth’s magnetic field and solar activity on galactic radiation levels. The program also 

calculates the effective dose rate from galactic cosmic radiation at any location in the atmosphere 

at altitudes up to 60,000 feet. The Web sites for CARI-6 are: 

http://jag.cami.jccbi.gov./cariprofile.asp; and 

http://www.faa.gov/education_research/research/med_humanfacs/aeromedical/radiobiology/cari

6/index.cfm. 

(2) CARI-6M. This program does not require a great-circle route between origin and 

destination airports; it allows the user to specify the flight path by entering the altitude and 

geographic coordinates of waypoints. The Web site for CARI-6M is: 

http://www.faa.gov/education_research/research/med_humanfacs/aeromedical/radiobiology/cari

6m/index.cfm. 

b. How to Reduce Exposure. The amount of radiation exposure received while flying 

depends on the amount of time in the air, altitude, latitude, and solar activity. (Provided air 

carriers respond to solar radiation alerts, ionizing radiation from the sun should not contribute 

enough additional radiation to exceed recommended exposure limits.) 

10. RADIOACTIVE MATERIAL SHIPMENTS. In calculating total exposure to ionizing 

radiation, consider exposure to radioactive cargo in addition to exposure to galactic cosmic and 

solar radiation. The carriage of such cargo is limited and controlled by the following regulations: 

a. Radiation Level Limitations. Title 49 of the Code of Federal Regulations (49 CFR) 

part 175, section 173.441. 

b. Notification of Pilot in Command. Title 49 CFR, part 175, section 175.33. 

c. Special Limitations and Requirements for Class 7 (Radioactive) Materials. 

Title 49 CFR part 175, section 175.700. 

11. FURTHER INFORMATION. 

a. For questions regarding in-flight radiation exposure, contact: 

U.S. Department of Transportation 

Federal Aviation Administration 

Office of Aerospace Medicine 

Radiobiology Research Team, AAM-610 

Civil Aerospace Medical Institute 

Oklahoma City, OK 73125 

9-amc-aam610-radiation@faa.gov. 
AC 120-61A 7/6/06 

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http://www.faa.gov/education_research/research/med_humanfacs/aeromedical/radiobiolo

gy/index.cfm. 

b. For questions regarding radioactive cargo contact: 

U.S. Department of Transportation 

Pipeline and Hazardous Materials Safety Administration 

Office of Hazardous Materials Technology 

Radioactive Materials Branch, PHH-23 

400 Seventh Street SW 

Washington, DC 20590 

http://hazmat.dot.gov

ORIGINAL SIGNED BY 

CAROL E. GILES (for) 

James J. Ballough 

Director, Flight Standards Service