Tower, Delta 191 heavy, out here in the rain, feels good. 191 heavy, we're not getting any bad warnings from the weather or from other pilots, which we rely on as they come through it. As the pilots of Delta 191 prepare for landing, the rain begins to fall harder. At the foot of the runway, one of the most ferocious types of storm clouds stands in their way. Before landing check, landing gear down, three green.

At the time, the type of storm the Delta crew is approaching barely has a name. John McCarthy is one of the world's leading experts on these storms. It is a tiny thing, meteorologically speaking, compared to a big storm or snowstorm or a hurricane. It's just like a needle in a haystack. The needle is a microburst, one of the deadliest and at the time, most poorly understood weather phenomena. They've taken down airliners before, but as Delta 191 makes its approach, there are no warning systems that can effectively alert the pilots of the danger they're in.

Prior to 1985, the radars on board the aircraft were built to detect thunderstorms, essentially heavy areas of precipitation. They were not effective; they were not even designed to detect the Micro Burst. If you're at the kitchen sink and you turn on the water and it goes straight down and it splashes out in all directions, that's kind of what a microburst is, except that it is extremely bad news if you're an airplane flying through it. When a plane hits a microburst, it encounters a complex and powerful set of conditions. Downdrafts and tailwinds batter a plane; it's a deadly combination.

Just short of the runway, Delta 191 flies into the microburst. "You're going to lose it, all of a sudden, there it is. Push it up, push it way up, way up, way up, way up, hang on to the son of..." The pilots of Delta Flight 191 did their very best to recover from this situation, and it didn't work out. "I must have caught sight of him just at the last millisecond, and he cartwheeled into the tank." In just an instant, and then, of course, there was fire, not a ball of fire, but a wall of fire.

Just 27 people survived the crash of Delta 191, 137 people are killed. After the crash of Delta 191, the Federal Aviation Administration races to develop technology that can prevent microbursts from killing again. If there is one crash that we can look back on now and say this made things safer because we learned from it, it was Delta 191.