A week after the catastrophic crash at the Reno Air Races that killed 11 people and injured dozens more, the National Transportation Safety Board (NTSB) today released its preliminary report on the incident. While the report revealed little new information of note, it confirmed the most salient details and laid the groundwork for a longer report that will take approximately a year to complete. Only when that final report is issued will the NTSB make recommendations that may affect future running of the Reno races—or, possibly, cause them to be shut down.

To piece together a fuller picture of what exactly went wrong, PM talked with officials, racers, and race crew personnel. The consensus to emerge is that the disaster was the direct result of the failure of a relatively small piece of metal, the elevator trim tab, that had been implicated in a number of similar incidents in the past. That failure-prone component, combined with a stroke of bad luck, turned a multimillion-dollar racing machine into an unguided missile.

Here's how, and why, we think the accident unfolded:

The P-51, the plane Jimmy Leeward crashed a week ago, was designed in the early 1940s as a long-range bomber escort and ground-strike aircraft that could cruise for more than a thousand miles at 360 mph. But for air racing, the planes are heavily modified to maintain speeds near 500 mph. At these speeds, the tail generates enormous downward pressure, and as a result, the nose wants to rise. Keeping the nose down would require constant physical exertion by the pilot. So, like any pilot in this situation, Jimmy Leeward would have engaged a flap on the back of one of the plane's elevators (the horizontal moving surface on the tail). Called the "elevator trim tab," this piece, in effect, reduces the elevator's angle of attack and thereby reduces the downward pressure.

To steady the P-51 at full racing speed, the trim tab has to deploy outward nearly as far as it can. Pushed out into the high-speed airstream, it's vulnerable to rapid vibration called flutter. The back-and-forth flexing can quickly cause severe metal fatigue; think of bending a paper clip back and forth until it breaks. Leeward's plane, the Galloping Ghost, had already completed several laps and was heading for the home pylon in a steep left turn when, the NTSB report says, "witnesses reported and photographic evidence indicates that a piece of the airframe separated." This is the trim tab falling off.

Without it, the Galloping Ghost suddenly lurches into a severe climb. Leeward would have experienced acceleration of at least 10 g's—enough to knock him unconscious. Back in 1998, a similar accident struck another P-51 at Reno, Voodoo Chile, during an Unlimited race in 1998. Pilot Bob Hannah blacked out during the 10 g ascent. By the time he came to, his plane had climbed to 9000 feet.

Andy Chiavetta, who worked with the pit crew of another Unlimited racer, says that according to telemetry broadcast from the Galloping Ghost to Leeward's team, the g load was far higher than that. "From what I understand he hit 22.5 g's, which no pilot can take," Chiavetta says. At that point, the crushing force pulls a pilot down so far that he or she isn't even visible in the canopy in pictures taken from the ground.

With the plane out of control and the engine still delivering full power, the Galloping Ghost rolls over and dives toward the ground at near maximum speed. The accident happens in the worst possible part of the entire 8-mile course—just before the spectator stand, leaving the aircraft on a collision course with the event's 7500 spectators.

The NTSB report puts the final result in cold, official language: "The airplane descended in an extremely nose-low attitude and collided with the ground in the box seat area near the center of the grandstand seating area."

However, a couple of lucky breaks kept the death toll from reaching higher. First, the plane hit the edge of the crowd rather than the center. And the impact happened so fast that the fuel didn't catch fire, which avoided a deadly conflagration. Above all, the plane remained intact, despite the severe g loads.

Had Leeward's plane come apart, the situation would have been even deadlier. In 1999, another highly modified P-51 called Miss Ashley II, piloted by Gary Levitz, lost its trim tab during an Unlimited race. It pitched violently upward just as Galloping Ghost did. "When it went vertical, the plane broke up," Chiavetta says. "The engine came off, the wings broke, it pretty much shredded the airplane in the air. It was very lucky that this plane didn't do that, because it would have put a debris field over the crowd"—in essence, a giant shotgun blast of metal and fuel.

Jeff Wise is a contributing editor for Popular Mechanics and the author of Extreme Fear: The Science of Your Mind in Danger. For a daily dose of extreme fear, check out his blog.

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