Magnetic Fields on the Flight Deck

Air Line Pilot, January 2001, p.21
By Gary C. Butler and Joyce S. Nicholas

Airline pilots operate within an environment that exposes them to magnetic fields generated by the airplane’s electrical system. Pilots are also exposed to cosmic radiation, sound, vibration, reduced atmospheric pressure, mild hypoxia, low humidity, and circadian disrhythmia. These occupational exposures may physiologically challenge the long-term health of airline pilots. Given the complexity of the environment and the possibility of synergistic effects, learning the amount of each exposure is necessary for evaluating any potential health risk.

In regard to magnetic fields, our research group, in a preliminary 1998 study of several airplane types, found that magnetic field strength varies with stages of flight, location within the airplane, and type of airplane. In general, the magnetic field strength at passenger positions tends to increase as one approaches the front of the airplane, suggesting that exposures to pilots on the flight deck might be higher than exposures to passengers. The objective of our latest study was to directly measure magnetic fields to which airline pilots are exposed in the cockpit when flying different airplane types during a month when the pilots flew 75 block hours.

We measured, with the Emdex II personal dosimeter, magnetic fields on the flight decks of four airplane types—B-737-200, B-747-400, B-767-300ER, and A320—during normal commercial operations.

The Emdex II personal dosimeter that we used in this study was calibrated at 60 hertz (Hz) with units in milligauss (mG); 1 mG = 0.1 microtesla. This dosimeter can measure magnetic fields in the range 0.1 to 3,000 mG, with an optimal resolution of 0.1 mG and a measurement accuracy of ±2 percent. The dosimeter was set to measure automatically in two frequency ranges, broad-band (40–800 Hz) and harmonic (100–800 Hz).

Volunteer study participants, who were either captains or first officers of Canadian Airlines International, wore personal dosimeters at hip level. Captains were asked to wear dosimeters on the right side and first officers on the left (this was intended to produce a consistent dosimeter position near the center of the flight deck). Information recorded for each flight segment included status as captain or first officer, date, city pair, airplane type, meter on/off times, time the airplane left the gate before takeoff, time of takeoff, time of landing, time the airplane returned to the gate after landing, and all time (with location) spent away from the flight deck.

The airplane types used in our study represent several kinds of flight deck technology. The flight deck of the B-737-200 has analog instruments. In contrast, the B-747-400 and the A320 have cathode ray tube (CRT) screens—two each for both the captain and the first officer. The CRTs depict flight characteristics and navigation parameters, with a center panel screen illustrating engine parameters and system management. The B-767-300ER has CRT screens with some analog instruments for back-up.

We analyzed data by airplane type, with statistics based on block hours, that is, beginning when the airplane left the gate before takeoff and ending when the airplane returned to the gate after landing.

Having previously found that measured magnetic field strength varies with type of airplane, stages of flight, and pilot location, we took measurements over approximately 1,008 block hours at a sampling frequency of 3 seconds (see Table I). The similarity between broadband and harmonic resultant values suggests that the fields being measured lie in the harmonic range (see Tables II–IV). For measurements taken during block time, harmonic geometric means ranged from 6.7 mG for the B-767-300ER (99 percent of harmonic measurements below 13.9 mG) to 12.7 mG for the B-737-200 (99 percent of harmonic measurements below 30.1 mG) (see Table III).

Because magnetic field strength decreases with distance from the source, measurements taken by captains were compared to measurements taken by first officers.

The geometric harmonic means differed by less than 1 mG between captains and first officers on the same airplane type (see Table IV).

Flights on the B-747-400 averaged 9.4 hours in duration, requiring bunk time for the pilots. For a typical flight onboard the B-747-400, the captain wore the personal dosimeter on the right hip. Block time for a single flight was separated into seven parts, each labeled with the captain’s location. On this flight, the field strength was much higher in the lower bunk than in the upper bunk. Pilot records from other B-747-400 flights indicate that some bunks were equipped with electric heaters, but we had no consistent information about when these heaters were on or off. Recalculating the harmonic geometric mean for all B-747-400 flights with bunk time removed produces a reduction in this group mean from 11.0 mG (geometric standard deviation 2.0) to 10.1 mG (geometric standard deviation 1.7).

We also took flight deck measurements and found field variation with stages of flight for typical flights on the B-737-200, the B-767-300ER, and the A320.

In two consecutive flights of the B-737-200, an extreme drop in the captain’s magnetic field exposure—to almost no exposure—occurred when the captain was not in the airplane between flights; and during the second flight, a spike in exposure—to 25 mG—occurred when the captain was in the lavatory.

During a single flight of a B-767-300ER, the exposure twice dropped moderately—to a range of 1.5 to 5 mG, from the regular range of exposure of 4 to 12 mG—when the first officer was in the lavatory and in the forward galley.

In a single flight of an A320, with the first officer wearing a personal dosimeter on the left hip, the exposure that was measured ranged between 5 and 18 mG, with no large spikes or drops.

The similarity between broadband and harmonic resultant values of our measurements suggests that the fields being measured lay in the harmonic range (see Table II). The higher harmonic frequencies could have biological significance in that higher frequencies induce stronger currents in human tissues. Total block time exposure of the pilots, including time spent in bunks, lavatories, or passenger compartments, varies in terms of geometric harmonic mean as follows: B-737-200 (analog technology), 12.7 mG; B-747-400 (CRT technology), 11.0 mG; A320 (CRT technology), 8.1 mG; and B-767-300ER (mixed analog and CRT), 6.7 mG (see also Table III). Differences in personal dosimeter measurements across aircraft types can be explained in part by technological differences, but also by differences in the pilots’ typical in-flight activities. For example, the average flight duration for the B-747-400 is more than 9 hours, requiring bunk time for the pilots. In contrast, pilots of the B-737-200 and the A320 rarely leave the flight deck during the shorter flights of less than 4 hours.

According to the U.S. National Institute of Environmental Health Sciences, the geometric mean personal exposure for individuals in the U.S. population is 0.8 mG for time at home (not in bed) and 1 mG at work. Our study indicates that less than 1 percent of flight deck measurements fall within this range. Airline pilots fly approximately 75 block hours per month and retire at age 60. This schedule constitutes the potential for long-term exposure to magnetic field levels substantially above those typically found in the home or office.

The interaction of humans with magnetic fields is complicated and has been the subject of much study and debate. In 1992, under the Energy Policy Act, the U.S. Congress instructed the National Institute of Environmental Health Sciences (NIEHS), the National Institutes of Health, and the U.S. Department of Energy to direct a program of research and analysis aimed at providing scientific evidence to clarify the potential for health risks from exposure to extremely low frequency (3 Hz–3 kHz) electric and magnetic fields (ELF-EMF). This resulted in the formation of the EMF-RAPID Program (Electric and Magnetic Fields Research and Public Information Dissemination Program). Using criteria developed by the International Agency for Research on Cancer, the working group concluded in a 1999 report that exposure to power-line frequency ELF-EMF is a "possible" human carcinogen.

In general, the NIEHS believes that ELF-EMF exposures show weak evidence of possible health effects; however, certain areas warrant notice for further research: childhood leukemias and adult chronic lymphocytic leukemia, cardiovascular deaths resulting from arrhythmia and acute myocardial infarction, neurodegenerative diseases (specifically amyotrophic lateral sclerosis and Alzheimer’s disease), and the effect of ELF-EMF on the action of melatonin and tamoxifen.

The World Health Organization, through its own international program on ELF-EMF, will review this field in 2003, with the NIEHS acting as a partner in the process.

Biological mechanisms for potential health effects, and therefore the most appropriate EMF unit of measure, have not been clearly identified. Studies of health outcomes among both military and airline pilots have suggested that certain diseases occur at increased rates among these groups. Within this context, we have recently completed a study of self-reported health outcomes among approximately 10,000 ALPA pilots in combination with occupational exposure histories. This study will appear in a future issue of Air Line Pilot.

While the average flight deck magnetic field strength is substantially higher than that of the typical home or work environment, further research is warranted to determine whether occupational magnetic field exposure constitutes a health risk for flight crews, either independently or jointly with other exposures.

The authors would like to thank the airline pilots who volunteered to participate in this study, which was supported in part by funds from the U.S. Department of Energy cooperative agreement DE-FC02-98CH10902 and from ALPA.