Skift Take

The NTSB's latest findings come as United and Alaska reported some loose hardware in their initial inspections of the Boeing 737 Max 9s.

Federal officials investigating Friday’s Alaska Airlines door blowout are looking into whether the bolts meant to keep a door plug in place were ever installed, or went missing at a later stage. 

Four bolts should have kept the left door plug secure to prevent it from moving upwards and disengaging from the Boeing 737 Max 9, National Transportation Safety Board Chair Jennifer Homendy said during a Monday night press conference. 

Those four bolts were also missing when the NTSB recovered the door plug, making it unclear if they were ever there to begin with. 

“We don't know if they were there or if, again, they came out during the violent explosive decompression event,” Homendy said.

Rapid decompression

On Friday, the left door plug on the fuselage of an Alaska 737-9 for flig