Radiation Hazards in Commercial Aviation

DALLAS — We take a look at the effects of radiation in commercial aviation and the measures taken to limit its effect on passengers, Flight Crews, and aircraft.

Radiations are waves of energy that travel through a medium at various frequencies and energies. It can be categorized as ionizing or non-ionizing.

Non-ionizing radiation is found in the lower end of the electromagnetic spectrum including radio waves, microwaves, infrared, visible waves, and the lower part of ultraviolet waves and they have low frequencies and energies, therefore not harmful. 

Ionizing radiation, which includes x-rays, gamma rays, and ultraviolet waves, is characterized by high frequencies and energies strong enough to knock electrons out of their atoms [1].

Once interacting with the human body, ionizing radiation can alter the molecular architecture of human cells and tissues, resulting in life-threatening disorders. Additionally, aircraft avionics and communication devices can also be affected.

Effect of Radiation on Altitude and Latitude

The vast majority of radiation sources on Earth's surface are non-ionizing, and even those that are ionizing emit very little non-hazardous radiation.

However, crew and passengers who fly at cruise altitudes above 30,000 feet are also exposed to solar radiation and galactic or cosmic radiation, which are additional types of ionizing radiation. At 35,000 feet above the earth's surface, the radiation level might be up to 10 times higher than it is at sea level.

The earth's magnetospheric shielding, which protects against solar radiation, is strongest at the equator and weakens with increasing latitude before becoming feeble at the poles; hence, the effects of radiation also worsen with increasing latitude.

Because of these implications, the United Nations estimated in 2000 that working in an airline produced more radiation exposure than even working in a nuclear power plant.

When flying at high altitudes, not only passengers and crew members but also aircraft systems and other equipment are at risk from radiation exposure. Let's take a look at these in detail.

Human Risks

According to the World Health Organization's (WHO) International Agency for Research on Cancer (IARC), ionizing radiation exposure leads to cancer and reproductive issues, including miscarriages. It can also produce genetic disorders and eye defects like cataracts.

The chance of dying from cancer is estimated at 200 per 1,000 people in the US alone, but among airline crew members, radiation exposure from 20 years of high-altitude flying raises the risk to 225 per 1,000.

Moreover, according to research published by the US NLM and ARPANSA, airline pilots and cabin staff had nearly twice the risk of Melanoma and other skin cancers as the general population, with pilots having a higher risk of dying from Melanoma.

Avionics

Cosmic radiation can induce soft errors in semiconductor devices that make up the avionics systems of aircraft. They can reverse digital bits and create undesirable signals to operate the aircraft.

As an example, On October 7, 2008, Qantas (QF) Flight 72 made an emergency landing at Learmonth Airport near the town of Exmouth, Western Australia following an inflight accident that included a pair of sudden, uncommanded pitch-down maneuvers that caused severe injuries—including fractures, lacerations, and spinal injuries—to several of the passengers and crew.

A number of potential trigger types were investigated, including software bugs, hardware faults, and electromagnetic interference. Secondary high-energy particles generated by cosmic rays, which can cause a bit flip, were also investigated.

These triggers were later said to be unlikely to have been involved, though a definitive conclusion could not be reached. A much more likely scenario was that a marginal hardware weakness of some form made the units susceptible to the effects of some type of environmental factor, which triggered the failure mode.

The ATSB's final report, issued on December 19, 2011, concluded that the incident because of design limitations and "in a very rare and specific situation, multiple spikes in the angle of attack (AOA) data from one of the ADIRUs could result in the FCPCs commanding the aircraft to pitch down."

High-Frequency Comms

High-frequency (HF) radio communications can be impaired or even completely interrupted by solar radiation. The ionization of the upper atmosphere (ionosphere), which absorbs shortwave radio communications, is increased when X-rays from solar flares enter the magnetosphere undeflected and reach the earth's atmosphere on the side facing the sun.

The magnetosphere deflects the impinging solar particles and directs them toward the poles of the planet, increasing the rate of ionization in the upper atmosphere and causing ionospheric absorption, hence disrupting HF radio communications with comparable effects.

During the October-November 2003 Halloween Storms, a series of solar storms involving solar flares and coronal mass ejections that generated the largest solar flare ever recorded by the GOES system, HF communications with airplanes encountered interruptions and later a complete breakdown of HF services that lasted for hours.

Mitigating Strategies

Passengers and Flight Crew

The International Commission on Radiological Protection (ICRP) is the primary body in charge of protecting against ionizing radiation and recommends an individual's effective dose limit of 20 mSv per year, averaged over defined 5-year periods (100 mSv in 5 years), with the additional restriction that the effective dose should not exceed 50 mSv in any single year.

Additionally, the recommended dose for pregnant crew members is 1 mSv from the time of pregnancy discovery until birth, with a monthly maximum of 0.5 mSv. The annual limit for the general public (passengers) is 1 mSv [6].

It is recommended that pregnant passengers and Flight Crew members think about trip-trading or delaying a journey to lower their risk of miscarriage. According to a National Institute for Occupational Safety & Health (NIOSH) study, miscarriage risk increases when women are exposed to cosmic radiation of at least 0.36 mSv during the first trimester.

Further, the Personnel Licensing Regulation Part 138 mandates that pregnant pilots and cabin crew be evaluated and excluded from flying duties between the time of pregnancy's discovery and the end of the 12th week of gestation, as well as between the end of the 26th week of gestation and delivery, in order to protect them from the effects of radiation exposure and other effects [4].

Airlines

Airlines choose a route and altitude that reduces radiation exposure after receiving a solar radiation alert(s) during moderate, strong, and severe transient solar radiation events (20 uSv/hr and above).

A solar radiation alert is transmitted worldwide and is accompanied by a message with estimates of radiation levels at altitudes from 20,000ft to 80,000ft at specific latitudes. 

Also, an individual can find out the effective dose of ionizing radiation received in each flight using a downloadable computer program called CARI-6 or CARI-6M, which was developed at the FAA's Civil Aerospace Medical Institute. 

Aircraft

All aircraft that are designed to operate over 15,000m (49,000ft) must carry technology that can monitor and continually display the dose rate of all cosmic radiation being received as well as the cumulative dose for each flight, according to ICAO Annex 6, Provision 6.12.

According to ICAO Annex 6 regulation 4.2.11.5, the operator must keep track of all flights exceeding 15,000 meters (49,000 feet) in order to calculate the cumulative cosmic radiation dose each crew member received during a 12-month period. [5]

Featured image: Boeing 737 wing view. Photo: Matthew Calise/Airways

References: [1] International Civil Aviation Organization-ICAO, Manual of Civil Aviation Medicine-Doc 8984, page II-1-13. [2] Matthias M. Meier , Kyle Copeland, Klara E. J. Klöble, Daniel Matthiä,Mona C. Plettenberg,Kai Schennetten,Michael Wirtz, and Christine E. Hellweg, Radiation in the Atmosphere—A Hazard to Aviation Safety?, Page 14. [3] International Civil Aviation Organization-ICAO, Manual of Civil Aviation Medicine-Doc 8984, page II-1-14. [4] Tanzania Civil Aviation Authority-TCAA, The Civil Aviation Personnel Licencing Regulations, 2017 part 138, page 230. [5] International Civil Aviation Academy-ICAO, Annex 6 Operation of Aircraft, Part I - International Commercial Air Transport - Aeroplanes, Ninth edition, July 2010, pages 6-13. [6] International Civil Aviation Organization-ICAO, Manual of Civil Aviation Medicine-Doc 8984, page II-1-15.