Itâ€™s long been known that flight at high altitudes exposes flight crew and passengers alike to greater levels of radiation than they normally experience on the surface, but a recent Harvard study on the prevalence of cancers among flight attendants has brought the subject into the spotlight once more. Itâ€™s been picked up by a wide variety of publications from outside the aviation world. To be honest, Iâ€™m a little surprised at their interest in the health of flight crew members.
If youâ€™re flying a real (aka light GA) airplane rather than a modern, automated turbojet, you might not have given the subject much thought. But turbojets operate near or above the tropopause (which varies in altitude from 23,000 to 65,000 depending on location and time of year). This places them well above most of the Earthâ€™s protective atmosphere, and therefore at greater exposure to direct sunlight, cosmic ionizing radiation, and so on. Unfortunately, the preventative measures we use on the ground â€“ sunscreen, long shirts, hats, sunglasses, etc. â€“ donâ€™t provide protection from all of these perils.
For an occasional passenger, the risk is fairly negligible. But for those of us who make their living working on an aircraft, the conclusions offered by this paper are quite concerning. The Harvard study, which has been ongoing since 2007, found the following:
â€œDespite low smoking and obesity levels indicative of positive health behaviors, we report that flight attendants have elevated rates of several cancers, especially breast, melanoma, and non-melanoma skin cancers. These results are consistent with previous findings regarding flight crew health. Ours is the first study to report an elevated rate of non-melanoma skin cancer in a U.S. flight attendant cohort (consistent with European studies). Some of these cancers were also related to tenure as a flight attendant, overall or within subgroups of parity in the case of breast cancer.â€
They also note that â€œâ€¦cabin crew have the largest annual ionizing radiation dose of all U.S. workers (e.g. 3.07 mSv vs. 0.59 mSv for U.S. Department of Energy workers). These exposures can easily exceed guidelines released by the NCRP or the International Commission on Radiological Protection.â€
The authors of the study donâ€™t claim to fully understand the impact of each risk factor, but I was impressed by their inclusion of other carcinogens flight attendants may be exposed to: pesticides, jet fuel, various chemicals found in uniforms, fire-proofed soft goods, and so on. They also noted the constant disruption to normal circadian rhythms as a risk factor for cancer.
As anyone whoâ€™s worked in the industry can probably tell you, the circadian issue is a major one when it comes to the adverse effect on fatigue, quality of life, and long-term health. Other studies have documented how an abnormal circadian rhythm disrupts the bodyâ€™s ability to fight of illness and disease at a cellular level. The body simply cannot work as designed when work schedules alternate randomly from night to day and back again.
Even when the schedule is steady, if itâ€™s a constant diet of night flying, the body suffers. I once asked a former long-haul cargo pilot if he ever got used to working at night all the time. His response: â€œNot really. You can always feel it sucking the life out of you.â€ This anecdotal evidence is backed up by scientific studies which have led the International Agency for Research on Cancer to classify shift work which disrupts normal circadian rhythms to be classified as â€œprobably carcinogenic to humansâ€.
Anyway, Iâ€™ve been asked about the Harvard study by several coworkers, who wonder about the correlation between flight attendants and the pilots up front. While the study did not address aviators directly, thereâ€™s no reason to suspect the folks in the cockpit are any better off when it comes to radiation exposure.
However, it seems logical to assume there may be significant differences in pilot risk depending on the kind of flying being done. A typical domestic Part 121 airline pilot might log 900 hours per year, whereas a charter pilot will only fly half that amount. There are plenty of Part 91 operators who fly 200 hours a year. Or less. Fewer hours at high altitude translate into reduced exposure to radiation.
On the other hand, some business aircraft fly much higher than a typical airliner. A Boeing or Airbus will ply the mid 30s, while many bizjets will climb directly into the low 40s, and can eventually reach as high as 51,000 feet if the weather requires it.
The trend with new business aircraft seems to be toward higher altitudes and longer ranges. While this capability is a boon for safety, it also means even greater exposure to radiation aloft. And as supersonic aircraft enter the inventory, it wouldnâ€™t surprise me to see these airplanes cruising around 60,000 feet.
Itâ€™s an exciting time to be part of the aviation industry, but the incessant march toward higher/longer/faster flying comes with risks, some of which may not yet be fully appreciated by those of us who will fly them.