By Valerie Insinna, Tim Hepher and David Shepardson

WASHINGTON (Reuters) – Aerospace provider Spirit AeroSystems (NYSE:) manufactured and initially put in the fuselage half on a brand-new Boeing (NYSE:) 737 Max 9 jet that suffered a blowout on Friday, however Boeing additionally has a key function within the ordinary completion course of, sources instructed Reuters.

Due to a fancy, two-tier set up course of, investigators are anticipated to look at whether or not any flaws occurred at Spirit’s large fuselage plant in Wichita, Kansas, or on the Boeing manufacturing facility exterior Seattle, the sources mentioned.

Regulators on Saturday grounded most Boeing 737 MAX 9s for security checks after the eight-week-old Alaska Airways airplane, carrying 171 passengers and 6 crew, misplaced a door-replacement panel throughout a U.S. flight, earlier than touchdown safely with a gaping gap in its aspect on Friday night time.

The 737 MAX 9, at present Boeing’s largest single-aisle, seating as much as 220 individuals, contains an elective further door to permit for the accepted variety of evacuation paths each time carriers choose to put in the utmost variety of seats.

However most airways utilizing the jet have chosen a looser format primarily based on a smaller variety of seats and don’t want the excess door, which provides weight and reduces flexibility within the cabin. As a substitute the door is deactivated earlier than supply, utilizing a “plug.”

Different elective doorways or fill-in substitute constructions had been additionally supplied on a predecessor mannequin, the 737-900ER.

As a part of the manufacturing course of, Spirit builds fuselages for 737s and sends them by prepare with the particular door meeting “semi-rigged,” one of many individuals mentioned.

“They’re fitted however not accomplished,” the particular person mentioned.

At its Renton, Washington, plant, Boeing sometimes removes the pop-out, or non-functioning, door and makes use of the hole to load interiors. Then, the half is put again and the set up in accomplished. Lastly, the hull is pressurized to 150% to verify every part is working accurately, the particular person mentioned.

The method implies that discovering out the place any flaw was launched throughout meeting might not be clear-cut, mentioned the sources, who requested to not be named as particulars of the probe are confidential.

Door plugs have been used to adapt plane and provide versatile layouts throughout the business for years.

The investigation will embrace structural specialists to see whether or not design or manufacturing performed a task within the accident.

“The idea is that it was put in or rigged incorrectly,” one of many sources mentioned.

Boeing and Spirit declined touch upon industrial processes.