On April 5, 2002, at 0845 mountain standard time, a Douglas/Basler DC-3C, N115Z, was substantially damaged when its left main landing gear collapsed while standing at Natrona County International Airport, Casper, Wyoming. The airline transport pilot, the commercial copilot, and one passenger were not injured. The airplane was being operated by the U.S.D.A. Forest Service, Boise, Idaho, under Title 14 CFR Part 91. Visual meteorological conditions prevailed for the public use cross-country flight that was preparing to originate at the time of the accident. An IFR flight plan had been filed. The pilot said that the airplane had taxied out for departure on runway 3. He said that he and his copilot were completing the checklist for departure when the copilot noticed high hydraulic pressure on the landing gear system. The copilot began the landing gear pressure relief procedure, but instead performed the landing gear retraction procedure. The pilot called out to the copilot to intervene, but the left main landing gear had already commenced retracting. The airplane settled onto its left wing damaging several intercostal ribs and wrinkling the left wing's skin. The copilot said that he had taken two capsules of an over-the-counter Federal Aviation Administration non-approved medication (Benadryl Allergy) on the morning of the accident. This medication, known as Diphenhydramine, commonly results in drowsiness, and has measurable effects on performance of complex cognitive and motor tasks. In Annals of Internal Medicine 2000; 132:354-363, states that the effect of a normal 50 mg dose of Diphenhydramine on simulated driving is noted to be worse than the effect of a 0.10% blood alcohol level.