The 787 engines made by GE can't fly in the rain. Where did you get that information?? Kind of curious as I retired in 2017 from working at Boeing on the Everett assembly plants flight line. The only issue I heard of was the gearbox issue and that's being resolved with a modified part.
It was a bulletin that we received I think it was in 2012 or 2013 about flying into thunderstorms I believe it had to do with ice crystals. It only affected 787s with GE engines and not the Rolls-Royce engines. I will see if I can find it.





