Nearly three weeks after a hole blew open on a Boeing 737 Max 9 during an Alaska Airlines flight, terrifying passengers, new details about the jet’s production are intensifying scrutiny of Boeing’s quality-control practices.
About a month before the Max 9 was delivered to Alaska Airlines in October, workers at Boeing’s factory in Renton, Wash., opened and later reinstalled the panel that would blow off the plane’s body, according to a person familiar with the matter.
The employees opened the panel, known as a door plug, because work needed to be done to its rivets — which are often used to join and secure parts on planes — said the person, who asked for anonymity because the person isn’t authorized to speak publicly while the National Transportation Safety Board conducts an investigation.
The request to open the plug came from employees of Spirit AeroSystems, a supplier that makes the body for the 737 Max in Wichita, Kan. After Boeing employees complied, Spirit employees who are based at Boeing’s Renton factory repaired the rivets. Boeing employees then reinstalled the door.
An internal system that tracks maintenance work at the facility, which assembles 737s, shows the request for maintenance but does not contain information about whether the door plug was inspected after it was replaced, the person said.
The details could begin to answer a crucial question about why the door plug detached from Flight 1282 at 16,000 feet, forcing the pilots to make an emergency landing at Portland International Airport in Oregon minutes after taking off on Jan. 5. The door plug is placed where an emergency exit door would be if a jet had more seats. To stay in place, the plug relies primarily on a pair of bolts at the top and another pair at the bottom, as well as metal pins and pads on the sides.
The Seattle Times reported earlier on Wednesday that Boeing had removed and reinstalled the door plug.
The F.A.A. on Wednesday approved detailed instructions for how airlines should inspect the door plugs on about 170 grounded planes. The instructions tell airlines to re-torque fasteners on the door plug, check the plug’s bolts and fittings, and fix any damage they find. Airlines can begin flying the jets again after completing the inspections.
United Airlines said it would begin inspecting its 79 Max 9 planes under the new guidelines and planned to start using them again on flights on Sunday. Alaska Airlines said it planned to put a “few planes” back into…