A San Diego plane crash last month shook the music world when it was discovered a famed producer and beloved metalcore drummer were killed … and now we have a better idea of what caused the tragedy.

TMZ broke the news that Daniel Williams — former drummer for the metalcore band The Devil Wears Prada — was among the six people killed in the May 22 crash.

According to an FAA preliminary report viewed by TMZ … authorities determined the pilot –believed to be well-known music producer Dave Shapiro — was flying the Cessna S550 too low due to poor weather conditions on his descent to Montgomery-Gibbs Executive Airport. The aircraft clipped power transmission lines about 90 feet high, 2 miles out from the runway — and plummeted into a neighborhood.

The FAA report notes the airport’s Automated Surface Observing System, a weather tool to guide aircraft on runway approach, was not working. The pilot acknowledged at the time he was aware of the issue, and continued his descent.

Daniel was not the current drummer of the popular Christian metalcore group … but his father, Larry, told us at the time his son was with them for years and was instrumental in the band’s massive success.