Originally Posted by
KenV
You're welcome.
That is also my understanding. The P&W engine uses an entirely new technology (a fan with reduction gears) and it is experiencing all sorts of early teething problems. It'll be interesting to see if the reduction gears really do provide the claimed/hoped for fuel burn reduction to justify the weight, drag, and complexity penalties. Time will tell. Boeing was more conservative and stuck to only GE LEAP engines on the 737MAX (and besides, the P&W engine with the larger diameter fan would not work on the 737 anyway) and thus avoided this added risk and complication. On the other hand, the A320neo is currently outselling the 737MAX, so maybe the risk was justified. We won't know until both the Airbus and the Boeing airplanes are in full rate production.
But the bottom line is that there really is no such thing anymore as a "simple" upgrade to generate a new airplane.
I used to think these new geared fans were a totally "new" technology but was intrigued to learn that the old BAe-146 has had them for over 30 years - they are effectively Chinook engines with geared fans stuck on them to create a high bypass turbofan.
https://en.wikipedia.org/wiki/Lycoming_ALF_502