Spirit Aero was involved in the explosion, but Boeing has a key role: sources By Reuters

By Valerie Insinna, Tim Hepher and David Shepardson

WASHINGTON (Reuters) – Aerospace supplier Spirit AeroSystems (NYSE:) initially manufactured and installed the fuselage part of a new Boeing (NYSE:) 737 Max 9 plane that suffered an explosion on Friday, but Boeing also has a key role in the usual completion process, sources told Reuters.

Because of a complex two-tier installation process, investigators are expected to examine whether any defects occurred at Spirit's giant fuselage plant in Wichita, Kansas, or at Boeing's factory outside Seattle, the sources said. .

Regulators on Saturday grounded most Boeing 737 MAX 9s for safety checks after the eight-week-old Alaska Airlines plane, carrying 171 passengers and six crew, lost a replacement panel. the door during a flight in the United States, before landing safely with a gaping hole in its side on Friday night.

The 737 MAX 9, currently Boeing's largest single-aisle aircraft, seating up to 220 people, includes an optional additional door to allow for the approved number of evacuation routes as long as airlines choose to install the maximum number of seats.

But most airlines using the plane have chosen a more flexible layout based on fewer seats and do not need the excess door, which adds weight and reduces flexibility in the cabin. Instead, the door is deactivated before delivery by a “plug”.

Other optional doors or infill replacement structures were also offered on a predecessor model, the 737-900ER.

As part of the production process, Spirit builds fuselages for 737s and ships them by train with the special door assembly “semi-equipped,” one of the people said.

“They are installed but not finished,” the person said.

At its Renton, Wash., plant, Boeing typically removes the pop-up or non-functioning door and uses the space to load interiors. The part is then replaced and the installation is complete. Finally, the helmet is pressurized to 150% to ensure everything works properly, the person said.

The process means that discovering where any defects were introduced during assembly may not be clear, said the sources, who asked not to be identified as details of the investigation are confidential.

Door plugs have been used to retrofit aircraft and offer flexible layouts throughout the industry for years.

The investigation will include structural experts to see if design or manufacturing played a role in the accident.

“It is assumed to have been installed or tampered with incorrectly,” one of the sources said.

Boeing and Spirit declined to comment on industrial processes.