DOT/FAA/AM-03/16

Offi ce of Aerospace Medicine

Washington, DC 20591

What Aircrews Should Know 

About Their Occupational 

Exposure to Ionizing Radiation

Wallace Friedberg

Kyle Copeland

Civil Aerospace Medical Institute

Federal Aviation Administration

Oklahoma City, OK 73125

This document is available to the public through the National 

Technical Information Service, Springfi eld, VA 22161.

Galactic

Cosmic

Radiation

Energetic 

SolarParticle 

Radiation
NOTICE

This document is disseminated under the sponsorship of

the U.S. Department of Transportation in the interest of

information exchange. The United States Government

assumes no liability for the contents thereof.
i

Technical Report Documentation Page 

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 

DOT/FAA/AM-03/16 

4. Title and Subtitle 5. Report Date 

October 2003 

6. Performing Organization Code 

What Aircrews Should Know About Their Occupational Exposure to 

Ionizing Radiation 

 7. Author(s) 8. Performing Organization Report No. 

Friedberg W, Copeland K 

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) 

FAA Civil Aerospace Medical Institute 

P.O. Box 25082 11. Contract or Grant No. 

Oklahoma City, OK 73125 

12. Sponsoring Agency name and Address 13. Type of Report and Period Covered 

Office of Aerospace Medicine 

Federal Aviation Administration 

800 Independence Ave., S.W. 

Washington, DC 20591 14. Sponsoring Agency Code 

15. Supplemental Notes 

Work was accomplished under approved task AM-B-03-TOX-204. 

16. Abstract 

Aircrews are occupationally exposed to ionizing radiation, principally from galactic cosmic radiation. A main 

source of galactic cosmic radiation is believed to be supernovae. On infrequent occasions, the sun contributes 

to the ionizing radiation received during air travel. Ionizing radiation consists of subatomic particles that, on 

interacting with an atom, can cause the atom to lose one or more orbital electrons or even break apart its 

nucleus. Such events occurring in body tissues may lead to health problems. For aircrews, and their children 

irradiated in utero, the principal health concern is a small increase in the lifetime risk of fatal cancer. For both 

of these groups, exposure to ionizing radiation also leads to a risk of genetic defects in future generations. The 

FAA recommends limits for aircrews in their occupational exposure to ionizing radiation and provides 

computer software for estimating the amount of galactic cosmic radiation received on a flight. 

17. Key Words 18. Distribution Statement 

Document is available to the public through the 

National Technical Information Service 

Aircrews, Ionizing Radiation, Galactic Cosmic 

Radiation, Cancer Risk, Hereditary Risks, Radiation 

Exposure Limits Springfield, Virginia 22161 

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price 

Unclassified Unclassified 11 

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized 

iii

ACKNOWLEDGMENTS

 For their assistance in the preparation of this report, we thank: Frances E. Duke, Oklahoma City, 

Oklahoma; Edgar B. Darden, Jr., Oak Ridge, Tennessee; Herbert H. Sauer, CIRES, University of Colorado and National Geophysical Data Center, NOAA, Boulder, Colorado; Keran O’Brien, III, Department of Physics and Astronomy, Northern Arizona University, Flagstaff, Arizona; and Michael E. Wayda 

FAA Civil Aerospace Medical Institute, Oklahoma City, Oklahoma.

1

Table 1. Average Annual Doses of Ionizing Radiation From Natural Sources Received by a 

Member of the Population of the United States (2)

 Effective dose,

 millisieverts

 Source (% of total)

 ________________________________________________________ 

 GALACTIC COSMIC RADIATION * . . . . . . . . 0.27 (9%)

 (Uniform whole-body exposure)

 RADIOACTIVE MATERIAL IN THE GROUND . . . . 0.28 (9%)

 (Uniform whole-body exposure) 

 INHALED RADON . . . . . . . . . . . . . . 2.0 (68%) 

 (Primarily to bronchial epithelium) 

 RADIOACTIVE MATERIAL IN BODY TISSUES . . . 0.40 (14%)

 (Tissue doses vary)

 Total from natural sources = 2.95 (100%) 

 ________________________________________________________ 

 * Includes 0.01 millisievert from air travel. 

WHAT AIRCREWS SHOULD KNOW ABOUT THEIR 

OCCUPATIONAL EXPOSURE TO IONIZING RADIATION

In a Presidential Document, Radiation Protection Guidance to Federal Agencies for Occupational 

Exposure, 52(17) Fed. Reg. 2822-2834 (1987), it is 

recommended that individuals who are occupationally 

exposed to ionizing radiation and managers of these 

activities, receive instruction on possible health effects 

associated with such exposure and on basic radiation 

protection principles. 

In 1994, the Federal Aviation Administration (FAA) 

formally recognized that air carrier aircrews are occupationally exposed to ionizing radiation and recommended that they be informed about their radiation 

exposure and associated health risks and that they be 

assisted in making informed decisions with regard to 

their work environment (1). The following questions 

and answers address subjects that aircrews should be 

familiar with concerning their occupational exposure 

to ionizing radiation.

1. What is ionizing radiation?

Ionizing radiation refers to subatomic particles that 

on interacting with an atom can directly or indirectly 

cause the atom to lose an electron or even break apart 

its nucleus. Such occurrences in body tissues may cause 

health problems. Examples of ionizing radiation are 

photons (X-rays and gamma rays), neutrons, protons, 

electrons, and positrons. Ionizing radiation is a normal 

part of our environment (Table 1). Substances that emit 

ionizing radiation are present in every cell in the body. 

We are exposed to ionizing radiation emanating from the 

ground and from some building materials. Ionizing radiation is used in some medical procedures, such as X-rays 

used to detect diseases of the chest and radioisotopes used 

for detecting and treating cancer. The principal ionizing 

radiation to which air travelers are exposed is galactic 

cosmic radiation, a main source of which is believed to 

be supernovae (exploding stars).
2

Outside the earth’s atmosphere, galactic cosmic radiation consists mostly of fast-moving protons (hydrogen 

nuclei) and alpha particles (helium nuclei). On entering 

the atmosphere, these particles collide with the nuclei 

of nitrogen, oxygen, and other air atoms, generating additional ionizing radiation particles. The particles that 

enter the atmosphere and those generated are collectively 

referred to as galactic cosmic radiation. At aircraft fl ight 

altitudes, the dose of galactic cosmic radiation received by 

air travelers is mainly from neutrons, protons, electrons, 

positrons, and photons. 

Occasionally a disturbance in the sun’s atmosphere 

(solar fl are, coronal mass ejection) leads to a surge of radiation particles with suffi cient energy to penetrate the earth’s 

magnetic fi eld and enter the atmosphere. The particles 

from such a solar disturbance interact with air atoms in 

the same way as galactic cosmic radiation particles. The 

result is that for varying amounts of time air travelers 

are exposed to both ionizing radiation from the sun and 

galactic cosmic radiation.

2. How can an airline minimize the risk of aircraft 

occupants being exposed to excessive amounts of ionizing radiation from the sun?

A Solar Radiation Alert system has been developed 

that considerably reduces the risk to air travelers of being exposed to excessive amounts of ionizing radiation 

following a severe solar disturbance. Accompanying an 

alert is a message with estimates of radiation levels at 

altitudes from 20,000 ft to 80,000 ft, at specifi ed high 

latitudes (map of specifi ed high latitudes on Web site 

identifi ed below), and a recommended maximum fl ight 

altitude at these latitudes.

http://www.cami.jccbi.gov/radiation.html 

Solar Radiation Alerts are transmitted worldwide to 

subscribers of the National Oceanic and Atmospheric 

Administration’s Weather Wire Service. For air-carrier 

aircraft, the recommended response to a Solar Radiation 

Alert is to minimize fl ight time at altitudes that exceed 

the recommended maximum fl ight altitude. 

3. What else about radiation from the sun is of 

interest to aircrews? 

Ionizing radiation from the sun cannot be avoided by 

fl ying only at night. Following a severe solar disturbance, 

ionizing radiation particles from the sun that reach the earth’s 

atmosphere are soon coming from all directions because of 

the spreading effect by the interplanetary and earth’s magnetic 

fi elds. If the ionizing radiation levels on the day and night 

sides of the earth start out appreciable different, they will 

be almost the same with 1 hour to a few hours. 

Long-distance communications are sometimes disrupted because of increased ionization of the earth’s upper 

atmosphere by X-rays, ultraviolet radiation, or protons 

from the sun. This can occur in the absence of excessive 

ionizing radiation levels at fl ight altitudes.

The Aurora Borealis and Aurora Australis (northern 

and southern lights) are colorful displays resulting from 

interaction of charged particles with air in the upper 

atmosphere. Such displays are not an indication of increased ionizing radiation levels at fl ight altitudes and do 

not present a hazard to air travelers.

4. How can aircrew members reduce their occupational exposure to ionizing radiation without working 

fewer hours?

Fly short fl ights at low latitudes. Short fl ights are fl own at 

lower altitudes than long-distance fl ights, hence there is 

more radiation shielding during short fl ights because of 

the greater amount of air above the aircraft. If two fl ights 

are fl own at the same altitude for the same length of time, 

but at different geographic latitudes, less radiation will 

usually be received on the lower-latitude fl ight because 

of the greater amount of radiation shielding provided by 

the earth’s magnetic fi eld. This shielding is maximum 

near the equator and gradually decreases to zero as one 

goes north or south (3). For example, during the period 

January 1958 through December 2002 at an altitude of 

30,000 ft, the average galactic cosmic radiation level over 

Reykjavik, Iceland (64o

 N, 22o W), was approximately 

twice that over Lima, Peru (12o

 S, 77o W).

5. What units are used to express amounts of ionizing radiation exposure?

When considering potential harmful health consequences from exposure to ionizing radiation, radiation 

dose is usually expressed in terms of effective dose (4). 

However, if the radiation is to a conceptus (any stage of 

prenatal development from the fertilized egg to birth), 

dose is expressed in terms of equivalent dose. The unit 

of both effective dose and equivalent dose (4) is the 

sievert, which is a measure of potential harm from ionizing radiation.

1 sievert = 1000 millisieverts

1 millisievert = 1000 microsieverts

The rem is another unit used to express potential harm 

from ionizing radiation. 

100 rem = 1 sievert

6.What are the recommended limits of occupational 

exposure to ionizing radiation for aircrews?

The FAA recommended limit for an aircrew member is 

a 5-year average effective dose of 20 millisieverts per year, 
3

Table 2. Effective Dose of Galactic Cosmic Radiation Received on Air Carrier Flights as 

Calculated with CARI-6 

 Single nonstop one-way flight 

 ------------------------------------------------ 

 Highest Milli-

 altitude, Air sievert

 feet in time, Block Milli- per block 

Origin–Destination thousands hours hours * sievert † hour ‡ 

 1 2 3 4 5 6

Seattle WA - Portland OR 21 0.4 0.6 0.00017 0.0003 

Houston TX - Austin TX 20 0.5 0.6 0.00017 0.0003 

Miami FL - Tampa FL 24 0.6 0.8 0.00039 0.0005 

St. Louis MO - Tulsa OK 35 0.9 1.1 0.00171 0.0016 

Tampa FL - St. Louis MO 31 2.0 2.2 0.00471 0.0021 

New Orleans LA - San Antonio TX 39 1.2 1.3 0.00327 0.0025 

Los Angeles CA - Honolulu HI 35 5.2 5.6 0.0147 0.0026 

New York NY - San Juan PR 37 3.0 3.4 0.0101 0.0030 

Honolulu HI - Los Angeles CA 40 5.1 5.5 0.0164 0.0030 

Los Angeles CA - Tokyo JP 40 11.7 12.0 0.0434 0.0036 

Tokyo JP - Los Angeles CA 37 8.8 9.3 0.0334 0.0036 

Washington DC - Los Angeles CA 35 4.7 4.9 0.0191 0.0039 

New York NY - Chicago IL 39 1.8 2.3 0.00892 0.0039 

Lisbon PG - New York NY 39 6.5 6.9 0.0289 0.0042 

London UK - Dallas/Ft. Worth TX 39 9.7 10.2 0.0437 0.0043 

Seattle WA - Washington DC 37 4.1 4.4 0.0192 0.0044 

Dallas/Ft Worth TX - London UK 37 8.5 9.0 0.0396 0.0044 

Chicago IL - San Francisco CA 39 3.8 4.3 0.0194 0.0045 

Seattle WA - Anchorage AK 35 3.4 3.7 0.0169 0.0046 

San Francisco CA - Chicago IL 41 3.8 4.3 0.0207 0.0048 

New York NY - Seattle WA 39 4.9 5.6 0.0280 0.0050 

London UK - New York NY 37 6.8 7.3 0.0374 0.0051 

New York NY - Tokyo JP 43 13.0 13.6 0.0754 0.0055 

Tokyo JP - New York NY 41 12.2 12.5 0.0696 0.0056 

London UK - Los Angeles CA 39 10.5 11.0 0.0616 0.0056 

Chicago IL - London UK 37 7.3 7.7 0.0430 0.0056 

London UK - Chicago IL 39 7.8 8.3 0.0475 0.0057 

Athens GR - New York NY 41 9.4 9.7 0.0613 0.0063 

* The block hours begin when the aircraft leaves the blocks before takeoff and end 

 when it reaches the blocks after landing.

† 45-year average effective flight-dose, January 1958 through December 2002. 

‡ Column 6 = Column 5 / Column 4 
4

Table 3. Increased Lifetime Risk of Fatal Cancer Because of Occupational Exposure to Ionizing 

Radiation *

 mSv † Risk mSv Risk mSv Risk

2 1 in 13000

(0.008%)

20 1 in 1300

(0.08%)

120 1 in 210 

(0.5%)

3 1 in 8300

(0.01%)

30 1 in 830

(0.1%)

140 1 in 180 

(0.6%)

4 1 in 6300

(0.02%)

40 1 in 630

(0.2%)

160 1 in 160 

(0.6%)

5 1 in 5000

(0.02%)

50 1 in 500

(0.2%)

180 1 in 140 

(0.7%)

6 1 in 4200

(0.02%)

60 1 in 420

(0.2%)

200 1 in 130 

(0.8%)

7 1 in 3600

(0.03%)

70 1 in 360 ‡

(0.3%)

225 1 in 110 

(0.9%)

8 1 in 3100

(0.03%)

80 1 in 310

(0.3%)

250 1 in 100 

(1.0%)

9 1 in 2800

(0.04%)

90 1 in 280

(0.4%)

275 1 in 91 

(1.1%)

10 1 in 2500

(0.04%)

100 1 in 250 

(0.4%)

300 1 in 83 

(1.2%)

* The risk of fatal cancer in a working-age population (20-64 years) because 

of occupational radiation exposure is estimated to be 4 in 100,000 per 

millisievert (0.004% per millisievert) (3). 

† mSv is the abbreviation for millisievert(s) 

‡ A risk of 1 in 360 from a dose of 70 millisieverts means 1 expected death 

from radiation-induced cancer for every 360 persons who each received a 

dose of 70 millisieverts.

with no more than 50 millisieverts in a single year (3). 

For a pregnant aircrew member starting when she reports 

her pregnancy to management, the recommended limit 

for the conceptus is an equivalent dose of 1 millisievert, 

with no more than 0.5 millisievert in any month (3).

7. How can an aircrew member fi nd out the effective dose of ionizing radiation received on a fl ight? If 

the crewmember is pregnant, how can she fi nd out 

the equivalent dose of ionizing radiation received by 

the conceptus? 

The computer program CARI-6 calculates the effective 

dose of galactic cosmic radiation received by a crewmember 

while fl ying an approximate great-circle route (the shortest 

distance) between two airports. Because of the penetrating nature of galactic cosmic radiation, the effective dose 

received by a pregnant woman is a reliable estimate of the 

equivalent dose received by the conceptus (3). There is an 

interactive version of CARI-6 that runs on the Internet and 

can be reached by a link from the Radiobiology Research 

Team Web site:

http://www.cami.jccbi.gov/radiation.html

Two versions of the CARI program, CARI-6 and 

CARI-6M, can be downloaded from the Web site. The 

downloadable version of CARI-6 is more sophisticated 

than the interactive version. In addition to calculating 

a fl ight dose, the downloadable version also allows the 

user to store and process multiple fl ight-profi les and to 

calculate dose rates at user-specifi ed locations in the 

atmosphere. CARI-6M does not require a great-circle 

route between origin and destination airports; it allows 

the user to specify the fl ight path by entering the altitude 

and geographic coordinates of waypoints.
5

8. What health concerns for aircrews are associated with their occupational exposure to ionizing 

radiation?

At the radiation doses received by aircrews, an increased 

risk of fatal cancer is the principal health concern (3). 

The following example shows how the increased risk 

can be estimated. Suppose a crewmember worked 700 

block hours per year for 25 years fl ying between New 

York, NY, and Chicago, IL (block hours defi ned in fi rst 

footnote to Table 2). Based on fl ight data in Table 2 and 

assuming the fl ight dose is the same in both directions, 

the effective dose of galactic cosmic radiation is 0.0039 

millisievert per block hour. In 25 years, the dose to the 

crewmember would be 68 millisieverts. 

25 years x 700 block hours per year x 0.0039 millisievert per block hour = 68 millisieverts

As seen in Table 3, crewmembers receiving 68 millisieverts will, on average, incur an increased lifetime risk 

of fatal cancer of about 1 in 360 (0.3%). In the general 

population of the United States in 1998, about 24% of 

adult deaths were from cancer (3). For an individual, a 

risk estimate is a rough approximation. 

Genetic defects passed on to future generations are a 

possible consequence of exposure to ionizing radiation 

(3). A child is at risk of inheriting genetic defects because 

of radiation received by the parents before the child’s 

conception. Suppose one of the child’s parents worked 

700 block hours per year for 5 years fl ying between New 

York, NY, and Chicago, IL, before the child was conceived. 

As in the previous example, the effective dose of galactic 

cosmic radiation received by the parent is assumed to be 

0.0039 millisievert per block hour. In 5 years, the dose 

to the parent would be 14 millisieverts.

Table 4. Increased Risk of Severe Genetic Defects in First-Generation Offspring Because of Parental 

Exposure to Ionizing Radiation Prior to the Offspring's Conception *

 mSv † Risk mSv Risk mSv Risk

10 1 in 25000 ‡

(0.004%)

110 1 in 2300 

(0.04%)

210 1 in 1200 

(0.08%)

20 1 in 13000 

(0.008%)

120 1 in 2100 

(0.05%)

220 1 in 1100 

(0.09%)

30 1 in 8300 

(0.01%)

130 1 in 1900 

(0.05%)

230 1 in 1100 

(0.09%)

40 1 in 6300 

(0.02%)

140 1 in 1800 

(0.06%)

240 1 in 1000 

(0.1%)

50 1 in 5000 

(0.02%)

150 1 in 1700 

(0.06%)

250 1 in 1000 

(0.1%)

60 1 in 4200 

(0.02%)

160 1 in 1600 

(0.06%)

260 1 in 960 

(0.1%)

70 1 in 3600 

(0.03%)

170 1 in 1500 

(0.07%)

270 1 in 930 

(0.1%)

80 1 in 3100 

(0.03%)

180 1 in 1400 

(0.07%)

280 1 in 890 

(0.1%)

90 1 in 2800 

(0.04%)

190 1 in 1300 

(0.08%)

290 1 in 860 

(0.1%)

100 1 in 2500 

(0.04%)

200 1 in 1300 

(0.08%)

300 1 in 830 

(0.1%)

* The risk of severe genetic defects in first-generation offspring, because 

of occupational radiation exposure of one or both parents, is estimated to 

be 4 in 1,000,000 per millisievert (0.0004% per millisievert) (3).

† mSv is the abbreviation for millisievert(s) 

‡ A risk of 1 in 25,000 from a dose of 10 millisieverts means 1 child is 

expected to have 1 or more severe genetic defects for every 25,000 

children born to parents who received a combined dose of 10 millisieverts 

prior to the child's conception.
6

Table 5. Increased Lifetime Risk of Fatal Cancer Because of Prenatal Exposure to Ionizing Radiation *

 mSv † Risk mSv Risk mSv Risk

1.0 1 in 10000 ‡

(0.01%)

1.6 1 in 6300 

(0.02%)

4 1 in 2500 

(0.04%)

1.1 1 in 9100 

(0.01%)

1.7 1 in 5900 

(0.02%)

5 1 in 2000 

(0.05%)

1.2 1 in 8300 

(0.01%)

1.8 1 in 5600 

(0.02%)

6 1 in 1700 

(0.06%)

1.3 1 in 7700 

(0.01%)

1.9 1 in 5300 

(0.02%)

7 1 in 1400 

(0.07%)

1.4 1 in 7100 

(0.01%)

2 1 in 5000 

(0.02%)

8 1 in 1300 

(0.08%)

1.5 1 in 6700 

(0.01%)

3 1 in 3300 

(0.03%)

9 1 in 1100 

(0.09%)

* The increased lifetime risk of fatal cancer for a child exposed to 

radiation during prenatal development is estimated to be 1 in 10,000 per 

millisievert (0.01% per millisievert) (3). 

† mSv is the abbreviation for millisievert(s) 

‡ A risk of 1 in 10,000 from a dose of 1 millisievert means 1 expected death 

from radiation-induced cancer for every 10,000 concepti, each of which 

received a dose of 1 millisievert.

5 years x 700 block hours per year x 0.0039 

 millisievert per block hour = 14 millisieverts

As seen in Table 4, with a parental dose of 14 millisieverts 

between 1 in 25,000 (0.004%) and 1 in 13,000 (0.008%) 

fi rst-generation children would be expected to inherit one 

or more radiation-induced severe genetic defects. In the 

general population, 2-3% of liveborn children have one 

or more severe abnormalities at birth (3). 

9. If an aircrew member works during pregnancy, 

what are the health risks for the child, and how long 

can the crewmember work before the dose of ionizing 

radiation to the conceptus exceeds FAA recommended 

limits?

Even if the dose to the conceptus were as high as 20 

millisieverts, no radiation-induced structural abnormalities or mental retardation would be observed (3). However, 

an increased risk of prenatal death could result from any 

dose of ionizing radiation during the fi rst day of development (3). The risk would depend on the precise stage of 

development at the time of irradiation and the radiation 

dose. If death did occur, the conceptus would most likely 

be aborted before the pregnancy was recognized. After the 

fi rst day or two, a dose as high as 20 millisieverts would 

not affect prenatal survival. 

A child irradiated during prenatal development will 

incur an increased lifetime risk of fatal cancer. Suppose 

a pregnant crewmember worked 70 block hours each 

month fl ying between New York, NY, and Chicago, IL, 

and the effective dose of galactic cosmic radiation is again 

assumed to be 0.0039 millisievert per block hour. With 

galactic cosmic radiation, the effective dose to the pregnant 

crewmember is a reliable estimate of the equivalent dose 

to the conceptus (see answer to question 7). Therefore, 

the estimated monthly equivalent dose to the conceptus 

is 0.27 millisieverts.

70 block hours per month x 0.0039 millisievert per 

block hour = 0.27 millisievert

This is well below the recommended monthly limit of 

0.5 millisievert (see answer to question 6). The dose to the 

conceptus would not exceed the recommended pregnancy 

limit of 1 millisievert as long as the crewmember worked 

no more than 3.7 months. 

1 millisievert / 0.27 millisievert each month = 3.7 months

As seen in Table 5, the increased lifetime risk of fatal 

cancer from 1 millisievert received during prenatal development is 1 in 10,000 (0.01%). In the general population 

of the United States (all ages) in 1998, approximately 

23% of all deaths were from cancer (3). 
7

Suppose the pregnant crewmember worked on highaltitude, high-latitude, long-distance fl ights between Athens, GR, and New York, NY. From fl ight data in Table 2 

and assuming the same fl ight dose in both directions, the 

effective dose to the pregnant crewmember, and therefore 

the equivalent dose to the conceptus, would be 0.0063 

millisievert per block hour. The pregnant crewmember 

could work 79 block hours each month without the dose 

to the conceptus exceeding the recommended monthly 

limit of 0.5 millisievert.

0.5 millisievert / 0.0063 millisievert per block hour = 

79 block hours

The pregnant crewmember could work 2 months 

without the dose to the conceptus exceeding the recommended pregnancy limit of 1 millisievert. 

1 millisievert / 0.5 millisievert each month = 2 months

CONCLUDING REMARKS

Although one cannot exclude the possibility of harm 

from occupational exposure to radiation at the doses 

likely to be received during a career of fl ying, it would 

be impossible to establish that an abnormality or disease 

in a particular individual resulted from such exposure. 

In estimating radiation-induced health risks for aircrews and their progeny, we used dose-effect relationships 

recommended by national and international organizations 

recognized for their expertise in evaluating radiation effects. However, considerable uncertainty exists in the estimates because the original data is primarily from studies 

on individuals exposed to radiation at much higher doses 

and dose rates and generally of lower energy than the 

galactic cosmic radiation to which aircrews are exposed. 

Also, controls were often inadequate. These differences 

are the major reason that epidemiological studies involving aircrews are important. 

With regard to occupational exposure to radiation 

during pregnancy, the FAA recommends that a pregnant 

crewmember and management work together to ensure 

that exposure of the conceptus not exceed recommended 

limits.

Under U.S. law, an employer may not limit, classify, or 

segregate an employee in any way that deprives or tends 

to deprive him or her of employment opportunities or 

otherwise affects the status of an employee because of 

sex or pregnancy. 

REFERENCES

1. Federal Aviation Administration, Crewmember Training 

on In-Flight Radiation Exposure, Advisory Circular 

120-61, May 19, 1994.

2. 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. 

 — Air travel, p.140. 

 — Average annual doses, p.148. 

3. 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.296-298.

 — 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.

 — Characteristics of a solar proton event, 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, pp.302 and 307.

 — Abnormalities at birth in the general population, 

pp.302 and 307.

4. Hall EJ, Radiobiology for the Radiologist. Fifth Edition 

2000, Lippincott Williams & Wilkins, Philadelphia, PA. 

 — Equivalent dose and effective dose defi ned, 

pp.236-237.