The World War II-era plane that plummeted into an air-race crowd like a missile bore little resemblance to its original self. It was rebuilt for speed, if not for stability.
The 65-year-old "Galloping Ghost" underwent years of massive overhauls that took a full 10 feet off its wingspan. The ailerons -- the back edges of the main wings used to control balance -- were cut from about 60 inches to 32.
Pilot Jimmy Leeward had said the changes made the P-51 Mustang faster and more maneuverable, but in the months before Friday's crash even he wasn't certain exactly how it would perform.
"I know it'll do the speed," he said in a podcast uploaded to YouTube in June. "The systems aren't proven yet. We think they're going to be OK."
Investigators don't yet know what caused the plane to pitch sharply into the crowd at the National Championship Air Races in Reno, killing nine people, including Leeward, and injuring dozens. They have focused on the "elevator trim tab" -- a piece of the tail that helps the aircraft maintain lift and appeared to break off before the crash.
In the highly competitive, bravado-filled world of air racing, pilots go for broke on the ground and in the sky, hitting speeds of 500 mph. Leeward is the 20th pilot to die at the air races since they began 47 years ago, but Friday's crash was the first in which spectators were killed.
"Pilots are a special breed of confident, intelligent, driven perfectionists," said Ken Quick, a commercial airline pilot and a crew member for one of the teams that raced Friday. "They know what they do is dangerous and demanding, and they eagerly embrace both."
Leeward's own website alludes to the dangers -- and bragging rights.
"These guys are always on the edge, knowing one wrong move, in one split second, could mean the end," the Leeward Air Ranch Racing Team website says. "NASCAR at 200 mph? Indy at 230 mph? Top Fuel at 300 mph? Mere Childs play. Welcome to the Big League."
Leeward had said the plane underwent several years of modifications before Friday's race, including lopping five feet off each wing, but he hadn't revealed many of the specifics. In the podcast, he called some of the changes "extremely radical," compared some to systems on the space shuttle and explained that he had increased the plane's speed capabilities to be more like those of a modern fighter jet.
Leeward was rounding a bend at dizzying speeds Friday when his plane took an oddly upward pitch, narrowly missing the packed grandstand. It then twirled just a few hundred feet off the ground and nose-dived into a section of VIP box seats, blasting out a 3-foot-deep, 8-foot-wide crater in a hail of metal, chairs and body parts.
Officials said 69 people were treated in hospitals, including 36 who have been released. Nine remained in critical condition Sunday.
FAA spokesman Ian Gregor said officials thoroughly vet all aircraft modifications before the planes are allowed to race. Reno Air Race Association technical experts also examine them to ensure they are air-worthy.
National Transportation Safety Board spokesman Terry Williams said his agency would look into the oversight of modifications to Leeward's plane as part of its investigation.