HAMPTON, Va. (WAVY) — Investigators looking into last week’s fatal plane crash at Langley Air Force Base in Hampton are focusing on a plug on a wing that may have come loose either on approach or during the crash.

The National Transportation Safety Board released a preliminary report into the April 24 crash, which killed the plane’s pilot, Rob Holland, 50, of Rob Holland Aerosports. The crash happened as Holland was attempting to land the plane ahead of the Air Power over Hampton Roads air show that was scheduled for that upcoming weekend.

The report stated that multiple witnesses observed the plane on a normal approach to the runway, watching it level off about 50 feet above the runway and flying straight down the runway for several hundred feet.

At that point, witnesses observed the aircraft bobbing up and down and rolling 90 degrees before it went straight toward the ground, crashing about 100 feet from the runway.

While all major components of the plane were accounted for at the crash site, the report highlighted a counterweight that was found dislodged at the crash site. That counterweight helps the aircraft perform more impressive aerobatics.

The report, however, does not state if the counterweight fell off in flight or at impact.

The aircraft’s last inspection was March 3 and was cited to have more than 1,000 hours of flight time.

The final report to conclude the cause of the crash will take at least a year.

Read the preliminary NTSB report below: