Boeing has refused to provide crucial records and information to investigators regarding the door plug that blew off a jetliner in January, raising concerns about quality assurance and safety management systems at the company. The National Transportation Safety Board (NTSB) chair expressed frustration over the lack of cooperation, while lawmakers called the situation "utterly unacceptable." The incident involved missing bolts that were discovered after a repair job, and Boeing's lack of transparency has hindered the investigation. The Federal Aviation Administration has given Boeing 90 days to address quality-control issues, following concerns about the company's safety culture.