Why problems at a key Boeing supplier may help explain the company's 737 Max 9 mess

At the factory in Wichita, Kan., where Spirit AeroSystems builds the fuselage for the Boeing 737 Max, management would sometimes throw a pizza party to celebrate a drop in the number of problems reported on the line.

But Joshua Dean says many of the workers knew something was off.

"We're having a pizza party because we're lowering defects," said Dean, a former quality auditor at the factory. "But we're not lowering defects. We just ain't reporting them, you know what I mean?"

Now federal investigators are looking more closely at to understand what went wrong with the door panel in the long and troubled relationship between the two companies.