The Federal Aviation Administration has opened another investigation into Boeing, adding to a string of safety agencies’ inquiries into the aircraft maker since a door plug blew off a 737-9 MAX in early January.

“The company voluntarily informed us in April that it may not have completed required inspections to confirm adequate bonding and grounding where the wings join the fuselage on certain 787 Dreamliner planes,” the FAA said in a statement.

The agency is looking into whether the Seattle-based airplane maker completed the necessary inspections for the Dreamliner and if employees falsified aircraft records. The FAA said Boeing is reinspecting all 787 aircraft that are still in production and will create a plan to address 787s that are currently in service.

"This is not an immediate safety of flight issue for the in-service fleet," Boeing Vice President of Manufacturing and Safety Scott Stocker said in an email to employees about the issue last week. 

No Boeing Dreamliner planes have been taken out of service or production.

In an earlier investigation of the Jan. 5 incident involving a Boeing 737-9 MAX operated by Alaska Airlines, the FAA reported that Boeing had failed to comply wih its own manufacturing quality control requirements in multiple instances regarding its 737-9 MAX planes, including its manufacturing process controls, parts handling, parts storage and product control.

The National Transportation Safety Board and U.S. Department of Justice are also investigating Boeing over the Jan. 5 incident.