Washington
CNN
 — 

Seven months of investigations. Nearly 10 hours of hearings. And yet neither Boeing nor the National Transportation Safety Board know how a 737 Max was delivered to Alaska Airlines without the four bolts needed to keep a door plug in place.

What is known: Boeing’s procedures and training – by employees, and by safety investigators – has drawn enormous skepticism and criticism from regulators. That was on full display in the first day of a two-day hearing. The NTSB called a rare public hearing to examine the near tragedy on the January 5 Alaska Air flight in which a door plug blew out, leaving a gaping hole in the…