The door to a pilot's plane appeared to be ajar as it took off from Fullerton Airport, moments before it crashed into a warehouse, according to investigators.

The NTSB said in its preliminary report that the pilot had made a “series of modifications” to the plane doors, which affected its “indicator system”

An amateur-built plane that slammed into a furniture warehouse near Fullerton Airport, killing the pilot and his teenage daughter and injuring 19 victims on the ground, had defects in a door that appears to have contributed to the collision.

A door was apparently not fully closed on a homebuilt airplane that crashed in Southern California earlier this month.

A witness saw the left main cabin door open during flight, and an examination of the door showed the interior handle was not in the locked position.

Authorities believe that plane door may have been open before the small jet ended up crashing into a Fullerton warehouse, killing the pilot and his daughter.