Originally Posted by bgriff

Z=RUC is not a published rule, so it's not an exception exactly, but it has been widely observed that there are issues on JFK-SEA where the system does not follow this "rule". It appears to have something to do with this route having once been Delta One-marketed, and Z does not equal RUC on D1 routes, and somehow that coding may still exist in Delta's systems. Since Z=RUC is not a published rule, there's not really any way to object to this or override it until Delta may eventually fix the system.