KUALA LUMPUR: American aircraft manufacturer The Boeing Company (Boeing) has shed light on what it believes was the cause of the incident involving the door plug that blew off of Alaska Airlines' B737 MAX-9 aircraft in January this year.
Boeing Commercial Airplanes senior vice president of quality Elizabeth Lund said the lack of paperwork was believed to be the root cause of the incident.
This led no one to be aware that the four bolts needed to hold the door plug of the aircraft in place were never installed before the plane left Boeing's final assembly line in October last year.
"The fact that one employee could not fill out one piece of paperwork in this condition and could result in an accident was shocking to all of us," she told reporters in a media briefing at Boeing's manufacturing facility in Renton, Washington.
In March this year, National Transportation Safety Board (NTSB) chair Jennifer Homendy said at a Senate hearing that Boeing did not provide the agency with the documents and information, specifically on the door plug needed to investigate the Alaska Airlines' incident.
Homendy added that the NTSB had not been able to interview the manager of the 25 people who worked with the aircraft door as the manager was on medical leave. She said Boeing also did not provide the names of the 25 workers.
Boeing then quickly clarified that the company cannot find documents about the door plug and said there was a possibility that the records never existed.
Lund confirmed this during the briefing and said that Boeing had discovered five non-confirming rivets when the fuselage arrived at the company's facility in Renton.
"These non-confirming rivets in and of themselves did not create a safety hazard but they were non-confirming and they needed to be fixed."
"A defect arrived from our supplier (Spirit AeroSystems Holdings Inc.) That airplane then travelled throughout the factory. moved to the end of the line while we discussed with our supplier back and forth – Are the rivets okay? Are they not okay? Do they need to be fixed? Can you fix them this way?" Lund said.
She explained that by the time the airplane reached at the end of the line of the facility, a decision was made that the mid exit door plug needed to be opened to get access to drill out the rivets and replace them.
The removal of a door plug after a plane arrives from its supplier Spirit AeroSystems rarely happens, Lund said.
"We believe the (door) plug was opened without the correct paperwork," she said as she explained that Boeing employees, known as the "move crew'" who opened and reclosed the door plug, were not at fault.
The door was supplied by Spirit AeroSystems and the mis-installation of the rivets was made at the supplier's MAX fuselage plant in Wichita, Kansas.
It was widely reported that the four retaining bolts in each corner of the door were not installed before the door plug was reclosed.
Without the bolts, the door moved slowly upwards while the B737 MAX-9 was in operation for nearly three months before blowing off mid-flight on Jan. 5.
"We know the move crew closed the (door) plug. They did not reinstall the retaining pins. That is not their job. Their job is to just close it (door plug) and they count on the existing paperwork. In this case, because we believe the paperwork was never created, there was no open paperwork that travelled with the airplane," Lund said.
She added that the move crew, a team who checks on airplanes before they roll out of the factory, ensures that any open holes on the aircraft are covered so that it's in good condition to go out in the weather.
On Jan 5 this year, an Alaska Airlines B737 MAX-9 aircraft had to make an emergency landing minutes after taking off from Portland, Oregon after its door plug blew out and left a gaping hole in the side of the narrow-body plane.
The crew managed to land the plane safely and no one onboard was injured.