The Hopkins team found that most alcohol-related plane crashes, 52 percent, occurred during nighttime hours, between 7 p.m. and 6 a.m. In contrast, most non-alcohol-related plane crashes, 72 percent, occurred during the day, between 7 a.m. and 6 p.m. Statistics also showed that 64 percent of alcohol-related crashes occurred in worsening weather conditions, such as rain or fog, which force the pilot to switch from visual flight rules to instrument flying.
The researchers hope their findings, to be published in the January issue of the journal Accident Analysis & Prevention, can be used to design programs similar to those that combat drunk-driving to lower accident rates.
"Pilots should never mix alcohol consumption with flying because it can impair their ability to think about key functions in operating a plane, such as interpreting flight instruments or coping with spatial disorientation," said lead study author and medical epidemiologist Guohua Li, M.D., Dr.P.H., professor of emergency medicine at The Johns Hopkins University School of Medicine and professor of health policy and management at the Bloomberg School of Public Health. "While regulations currently ban drinking and flying, only major airlines have programs in place for regular testing of pilots, and no program exists for the general aviation pilot."
To better understand the circumstances of and identify specific risk factors involved in alcohol-related plane crashes, the Hopkins team studied medical records for 313 general aviation crashes fatal to the pilot from 1985 to 2000. Specifically, the researchers separated the files using a cut-off blood alcohol concentration (BAC) of 20 milligrams per deciliter (0.02 percent BAC), the minimum reliably detectable level. A trained flight instructor then coded each case based on nearly 20 characteristics and circumstances, including age of pilot, type of flying certificate, total flight time experience, type of airplane, weather conditions, time of day, place and cause of crash.
The information came from a combination of databases at the National Transportation Safety Board and autopsy records from state medical examiners offices in three states - Maryland, New Mexico and North Carolina - whose coroners routinely perform toxicology tests on people who are fatally injured. Some of the 313 cases were excluded because of incomplete information.
Overall, the researchers found that 11 percent (25 cases) had positive BACs, and 6 percent (15 cases) had BACs above the legal limit of 40 milligrams per deciliter (0.04 percent BAC). Alcohol was listed as a contributing factor by the NTSB in eight of the 25 alcohol-related plane crashes, with BACs for these pilots ranging from 70 to 239 milligrams per deciliter. A total of 194 other people, mostly passengers, also died in these plane crashes.
While the two most significant risk factors were nighttime flying and worsening weather conditions, pilot error was recorded as a contributing factor in all of the alcohol-related crashes and in 96 percent of other crashes. These included cases where the pilot was "showing off" to friends by flying too low, or lost control of the aircraft in darkness or in bad weather.
"This study provides a better understanding of the role played by alcohol in fatal plane crashes, including identification of the risk factors, such as when and where disaster is most likely to strike," said study co-author Susan Baker, M.P.H., a professor of medicine at Hopkins and professor of health policy and management at the Bloomberg School of Public Health, who is also a certified pilot. "Our results provide additional evidence that 'zero tolerance' policies on alcohol are justified. Alcohol is a contributing risk factor in fatal plane crashes."
The researchers will now focus on nighttime flying in different weather conditions and develop test programs to improve aviation safety, such as routine spot checks, or checking on drinking behavior during pilots' biannual physical exams, that might help reduce alcohol-related crashes in the future.
Current federal regulations do not allow any person to operate any aircraft - major airlines, commuter aircraft, air taxis, or private planes - within eight hours after having consumed alcohol, or with a BAC above 40 milligrams per deciliter. Only major airlines are required to perform regular, random testing throughout the year, and on a minimum of 10 percent of employees with safety responsibilities, including pilots. While the number of alcohol-related infractions is low, statistics compiled by the Federal Aviation Administration indicate that about one person in 200 of the tested flight crew had BACs above the legal limit. In the 1960s, more than 30 percent of pilots who were killed in plane crashes had elevated BACs. Some studies have shown that this level dropped to 8 percent in the 1990s. In crashes of commuter aircraft or air taxis, measurable BACs were found in only three of 108 pilots who died between 1983 and 1988, and there are no cases where alcohol has been implicated as a probable cause in a fatal crash of a major U.S. airline. Currently, approximately 700,000 Americans are certified for general aviation and can pilot a plane.
Funding for the study was provided by the National Institute on Alcohol Abuse and Alcoholism, a part of the National Institutes of Health (NIH). Other researchers who took part in this study were Yandong Qiang and Melissa McCarthy, Sc.D., both from Hopkins; and Margaret Lamb, a flight instructor from Sunshine Aviation Safety Studies, in Alamosa, Colo.