The one-week summary of evidence collected following the crash at Reno-Stead Airport puts the number of injured at 74, 66 of them seriously.
The report makes no conclusions, and notes that investigators are trying to extract clues about the crash from ground crew telemetry reports, an onboard data box and camera equipment believed to be from the plane. A final report with findings is expected to take months.
Pilot Jimmy Leeward, 74, of Ocala, Fla., was among the 11 people killed in the crash during the National Championship Air Races.
Leeward was a veteran movie stunt pilot and air racer who spoke earlier about modifications he made to squeeze more speed from his P-51 Mustang fighter plane.
The NTSB cites photo and video evidence that a piece fell off the aircraft after Leeward completed several laps and made a steep left turn toward the home pylon and grandstand.
The plane banked suddenly left, then right, turned away from the racecourse, and pitched into a steep nose-high climb.
“Witnesses reported and photographic evidence indicates that a piece of the airframe separated during these maneuvers,” the NTSB said.
The plane then rolled and dove nose-first into a box seat area in front of the center of the grandstands.