Chuck Yeager, the famed test pilot, was flying an F-86 Sabre over a lake in the Sierras when he decided to buzz a friend’s house near the edge of the lake. During a slow roll, he suddenly felt his aileron lock. Says Yeager, "It was a hairy moment, flying about 150 feet off the ground and upside down."
A lesser pilot might have panicked with fatal results, but Yeager let off on the G’s, pushed up the nose, and sure enough, the aileron unlocked. Climbing to 15,000 feet, where it was safer, Yeager tried the maneuver again. Every time he rolled, the problem recurred.
Yeager knew three or four pilots had died under similar circumstances, but to date, investigators were puzzled as to the source of the Sabre’s fatal flaw. Yeager went to his superior with a report, and the inspectors went to work. They found that a bolt on the aileron cylinder was installed upside down.
Eventually, the culprit was found in a North American plant. He was an older man on the assembly line who ignored instructions about how to insert that bolt, because, by golly, he knew that bolts were supposed to be placed head up, not head down. In a sad commentary, Yeager says that "nobody ever told the man how many pilots he had killed." (From "Yeager" by Chuck Yeager, Bantam, 1985)