- Many pilots killed in noncommercial airplane crashes had taken medication
- The most common drugs were antihistamines and heart medications
- Drugs were not a factor in any of the fatal commercial crashes included in the study
Forty percent of all pilots killed in noncommercial airplane crashes in recent years have medication in their systems -- a marked increase over previous decades, according to a draft government study obtained by CNN.
The most common drugs: antihistamines, which can cause drowsiness, and heart medications.
The most worrisome: illicit drugs found in nearly 4% of the deceased pilots.
All told, pilots tested positive for some sort of drug -- be it over-the-counter, prescription or illicit -- in 40% of fatal accidents in 2011, up from 10% in 1990, according to the study.
The National Transportation Safety Board, which conducted the study, called the jump "significant," saying it mirrors medicine use in society as a whole.
It cautioned that the mere presence of drugs does not necessarily mean drugs contributed to the accident. Indeed, investigators say drugs contribute to about 3% of all fatal plane crashes -- a level that has remained constant for two decades.
But it said medications present special risks to pilots, and that risk is growing because of the increase in the use of potentially impairing drugs. The NTSB is expected to call for more research to better understand the problem, and more warnings for all types of pilots about the risks involved.
The board provided a copy of the draft report to CNN and is expected to adopt the report at its meeting Wednesday.
The safety board launched the study after observing the growing popularity of over-the-counter and prescription drugs in the general population. It wondered about drug use among aviators.
The study looked at 6,677 pilots killed between 1990 and 2012 for whom records are available. While commercial crashes were included in the study, drugs have not been a factor in any of the fatal commercial crashes, which are exceedingly rare. The vast majority of the fatal crashes fall into the category of general aviation, which includes virtually everything but military and airline flights.
Investigators found that pilot drug use mirrors that of the general population.
Cardiovascular drugs were detected in 12.4% of pilots in fatal crashes in 2008-2012, up from 2.4% in 1990-1997.
Antihistamines were detected in 9.9% of pilots in 2008-2012, up from 5.6% in 1990-1997. "Pilots may not appreciate the potentially impairing effects of diphenhydramine (antihistamine) because it is so widely used in cold and allergy products," the report says. "However, (the drug) can significantly impair performance."
Antidepressants were detected in 5.3% of deceased pilots in 2008-2012, up from 1.0% in 1990-1997.
Pilots are not necessarily prohibited from flying after using prescribed controlled substances, only from flying after recent use.
Some 3.8% of deceased pilots tested positive for illicit drugs from 2008-2012, up from 2.3% in 1990-1997, the report said. Marijuana was the most commonly identified illicit drug.
"Illicit drug use is particularly concerning to transportation safety because ... illicit drug users are often actively seeking the impairing effect of the drug," the study said.
The study did not look at alcohol use, partially because alcohol is produced by dead body tissue, making it difficult to determine if a pilot ingested alcohol prior to a fatal accident.
A 1983 cargo plane accident at Newark International Airport highlighted the problem of drug use. Post-accident tests showed one pilot had smoked marijuana and the other had taken phenylpropanolamine (a drug found in decongestants and diet aids at the time) within 24 hours before the accident. The safety board concluded that the drug use was a factor in impairing the crew's decision-making and flying abilities.
That accident prompted the Federal Aviation Administration to test deceased pilots for drugs. An FAA lab can now identify more than 1,300 different chemicals.
Accident investigators say a full understanding of drug use is needed to allow doctors and aviation businesses to inform pilots about "which drugs they may take, which drugs are prohibited, and the safest timing for each drug's use."
The NTSB staff said pilots need to be provided with precautionary information about the impairing potential of drugs. And additional research is needed about the relationship between drug use and accident risk.