"The authors studied the effects of
marijuana intoxication on the ability of 10 certified airplane pilots to operate a flight simulator. They used a randomized double-blind crossover design to compare the effect of active versus placebo
marijuana. They found that all 10 pilots showed a significant decrease in measurements of flying performance 30 minutes after smoking active
marijuana. For a group of 6 pilots tested sequentially for 6 hours, a nonsignificant decrease in flying performance continued for 2 hours after smoking the active drug." -
Marijuana effects on simulated flying ability