LAS VEGAS (AP) - A highly modified vintage aircraft was pushed beyond its structural limits before it crashed into spectators at last year's National Championship Air Races in Reno.

PHOTOS: Plane crash at Reno air race

That's among the findings being presented to the National Transportation Safety Board on Monday in Washington.

Loose screws on a crucial tail assembly are also blamed in the September 2011 crash that killed 74-year-old pilot Jimmy Leeward and 10 people on the ground and injured more than 70.

This year's Reno Air Races start Sept. 12.

The five-member NTSB has already issued several preliminary reports and recommendations for the Federal Aviation Administration and race organizers to improve safety.

NTSB officials say Leeward's World War II-era P-51 Mustang fighter reached 530 mph before it pitched skyward and then slammed nose-first into rows of box seats.

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