By Valerie Insinna, Tim Hepher and David Shepardson WASHINGTON (Reuters) – Aerospace supplier Spirit AeroSystems manufactured and initially installed the fuselage part on a brand-new Boeing 737 Max 9 jet that suffered a blowout 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 flaws occurred at Spirit’s giant fuselage plant in Wichita, Kansas, or at the Boeing factory outside Seattle, the sources said. Regulators on Saturday grounded most Boeing …