The worries about engine and parts shortage on the Boeing (BA) 737 program is something that is preying on many people's mind. We think that the current strain on the supply chain gives reason for valid concern about Boeing's ability to scale production even further. Now, why does this worry investors? The answer is pretty simple; Currently, the Boeing 737 program accounts for roughly 40% of all Boeing Commercial Airplanes revenues. It is also this aircraft segment that is best suitable for further scaling of production. If the scaling is restricted due to