I was looking for a Seinfeld thread I thought was fairly recent, but didn't find anything on the first 5 pages. The Airport episode from season 4 is where Jerry has it luxurious on a plane, but Elaine has lesser terrible seating in coach. Elaine was originally going to be sitting next to a stiff someone- cadaver stiff. NBC said that was too dark of a plot for even Seinfeld, so there was no corpse next to Elaine.
Yet I saw today that Murder, She Wrote had an episode title from 1986 called The Corpse Flew First Class. Murder, She Wrote aired in the 8PM family hour while Seinfeld was in the more adult 9PM hour. Only possible difference is it might be too morbid for a 90s sitcom, but so is killing off Susan and George practically celebrating.