Boeing Co’s decision to suspend aerospace’s biggest production line exposes contrasts in the US-dominated 737 MAX supply chain, severely straining some niche machine shops while giving engine giants time to iron out their own wrinkles. The temporary 737 MAX production halt, the latest fallout in a 9-month-old grounding crisis, has already kicked off tough negotiations between Boeing and Spirit AeroSystems Holdings Inc, Boeing’s largest 737 supplier, one industry source said. Wichita, Kansas-based Spirit has staffed its factory with enough workers to maintain a pre-crisis build rate of 52 aircraft per month and to enable a smooth step-by-step eventual increase to 57 aircraft, the person said. Now, furloughs in Kansas are likely if Boeing stops paying Spirit to build and store fuselages at those rates, the person said, adding that scenario was likely as Boeing looks to conserve cash. A second supply chain source agreed. “No way can they keep going,” he said. Spirit declined comment. A Boeing spokesman declined to comment on discussions with suppliers. He referred to a Monday statement that Boeing will work to “sustain the gains in production system and supply chain quality and health made over the last many months.” The fallout depends on how long Boeing’s freeze lasts, and how much if any compensation Boeing pays to prop up some of the roughly 680 suppliers that feed its best-selling program. Payments may not come quickly.