Originally Posted by
DaveReidUK
The proof of the pudding will be whether the 777X is grandfathered onto the current 777 Type Certificate. If it's essentially a new aircraft it won't and can't be.
AFAIK the DC9 and the B717 are the same type certificate, but the FAA denied Fokker the same for the F27 and the F50. Type Certificate doesn't mean as much as it should.