Cooper’s instructions for the southbound flight—gear down, unpressurized cabin, slow speed, low altitude—created conditions that were challenging for the aircraft but meaningful for someone planning to jump. A pressurized cabin at high altitude would make exiting the aircraft extremely dangerous; an unpressurized cabin at 10,000 feet was survivable. A slow speed reduced the physical forces a person would experience leaving the aircraft. The gear-down configuration reduced airspeed further. These were not random demands; they reflect at least some knowledge of what conditions would make a parachute exit survivable.
The temperature at altitude on that November night has been estimated by researchers at around 7 degrees Fahrenheit (approximately negative 14 Celsius), with wind chill in the parachute descent potentially much colder. Cooper was wearing a business suit, a raincoat, and loafers. He had no cold-weather gear, no gloves that were described, and no helmet. Whatever parachute he used was military surplus—adequate for a jump but not the refined equipment a trained sport skydiver would typically choose for a challenging nighttime landing in unknown terrain.
The aircraft crew did not see the jump happen. They were in the cockpit, door closed, following Cooper’s instructions. The instruments told them the aft stair had been deployed. The tail movement—the upward pitch—happened at approximately 8:13 p.m. local time. Later investigation by the FBI, using a test aircraft and a weighted sled dropped from the aft stair, confirmed that the upward tail pitch was consistent with a body or significant weight leaving the aircraft via the stair.