I don't think we're looking for longest trips over water, but longest forced routings over water because there are no other options. I'm thinking if you were delivering a plane from South American to Oceania you would have several route options that would allow for refueling stops along the way (up thorugh North America, then over to Hawaii and over all those islands between there and the final destination).

I wrote that the way I did because I know there's something unique about SFO to Hawaii, and figured someone would come up with the answer ...