[smallmind]

The weight and efficiency benefits of current composites vs aluminum lithium (AlLi) frames are not enough to justify their costs.

Also wide-bodies are just different from narrow bodies in length or diameter. Narrow bodies are designed to go through more and frequent pressurization cycles, fit and weigh enough for certain gates and runways, carry different amounts of cargo.

The other variable is the cost to build the plane you describe. The reason Boeing decided to rengine the 737 for the NG instead of the 757 is the 737 costs less to build and operate. The 737 MAX 8-200 and the MAX 10 are very economical to fly on a level a shrunken 787 couldn't reach.

It's also important to remember the 737 Max was kind of a stop gap on the higher capacity variants for the NMA. If Boeing had been willing to give the MAX a slightly different type rating and difference training for the MAX, MCAS would not have been necessary. Then the MAX 9 and 10 could be replaced by the NMA and bought Embraer with stretched E2 jets replacing the MAX 7 and 8 if executives were concerned with more than their annual stock comp.

[kayfox]

> If Boeing had been willing to give the MAX a slightly different type rating and difference training for the MAX, MCAS would not have been necessary.

I see this a lot, but MCAS would still be needed to comply with the regulations on control column force curves so I don't think Boeing could have just gotten a different type rating and done that.