"At an age when many people consider retiring, Robert E. Machol stopped teaching at Northwestern University and started a new career as chief scientist for the Federal Aviation Administration. There, while in his 70s, he predicted "catastrophe" after studying the turbulence created by the jet engines of 757 airplanes--work that predicted fatal crashes and eventually led to a change in federal aviation policy... "I was the first guy within the agency who got up and said, `We're likely to have a catastrophe, a real catastrophe … if we don't do something," Mr. Machol told the Los Angeles Times in 1994. Eventually, the agency ordered landing aircraft to maintain a greater distance behind 757s to avoid the jet's dangerous "wake vortex." But the policy change came only after crashes in Billings, Mont., and Santa Ana, Calif., that killed 13 people."