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Pilots’ Flying Ability Impaired For 24 Hours After Smoking Pot

November 8, 1985

LOS ANGELES (AP) _ Pot-smoking pilots suffered impaired flying ability a full day after they used marijuana - and one even missed a simulated runway - although they believed their performance was not harmed, a study found.

While the preliminary study involved only 10 pilots, it suggested that even experienced aviators ″had better stay out of a plane for at least 24 hours″ after smoking marijuana, Stanford University psychiatrist Dr. Jerome Yesavage said Thursday during a telephone interview.

″I’d watch out for the guy who smokes the night before and then flys in the morning, particularly in bad weather conditions,″ said Yesavage, who also is a licensed commercial pilot and chief of psychiatric intensive care at the Palo Alto Veterans Administration Medical Center.

The study, published in the November issue of the American Journal of Psychiatry, involved 10 licensed, private pilots recruited from Palo Alto’s airport, then trained for eight hours on a flight simulator at the Veterans Administration hospital.

All had smoked pot previously, but were not daily users.

Some of the 10 pilots in the study ″were out to prove a point - that they could fly just as well″ after smoking marijuana, Yesavage said. ″They didn’t prove their point.″

The researchers tested each pilot’s ability to use the simulator to take off, climb to 700 feet, make two turns, then descend and land. The test was repeated at one, four and 24 hours after each pilot smoked a cigarette containing 19 milligrams of THC, the active ingredient in marijuana.

The dosage was equal to about two strong marijuana cigarettes, Yesavage said, adding that the study ″raises a question about casual, social use of marijuana in highly technical employment″ such as heavy equipment operation.

One hour after the pilots smoked pot, ″there was a real question of getting back to the ground,″ Yesavage said. ″At four hours, people were still pretty shaky.″

Even 24 hours after smoking the drug, the pilots still showed significant impairment of flying ability - including the ability to land the simulated flight on a runway centerline - even though the pilots believed their performance was unimpaired, Yesavage said.

″One of the pilots did land off the (simulated) runway 24 hours after THC ingestion,″ the study said.

The pilots’ difficulty ″in aligning and landing precisely at the center of the runway is a particular cause for concern,″ the study said.

Twenty-four hours after they smoked pot, the average distance the pilots landed from the centerline of the simulated runway was twice the normal distance, it said.

″In actual flight, where there is wind and turbulence, such errors can easily lead to crashes,″ the study said.

The study found impairment in the pilots’ performance in landing, operating ailerons, which make a plane turn, and elevators, which control an aircraft’s up and down motion.

Yesavage cautioned that further study was needed to determine if impairment of flying ability as measured during simulated flight translated into actual impairment during real flight, although he said he believed it did.

Barbara Abels, a spokeswoman for the Federal Aviation Administration, said she was not familiar with the study.

But she said, ″Responsible pilots know what will happen if you mix drugs or alcohol with flying.″

The study was funded by the National Institute on Drug Abuse. Yesavage’s co-authors were Von Otto Leirer, a research associate at Stanford; Lt. Cmdr. Mark Denari, a former Navy safety officer; and Dr. Leo E. Hollister, a pharmacologist at Stanford and the VA hospital.

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