User blog comment:Menara/The Son of Sobek: The official PJ and Kane Chronicles Crossover/@comment-4902593-20130616074828

Here are my reasons why Percy won't call Carter to Tartarus:

1. Carter's life will be in danger: Of course, this sounds stupid, considering he is always in danger, but this is Tartarus, which is toooo dangerous, even for the Gods.

2. Carter's powers would be pretty useless: Sure, he went to the Land of Demons, which is the Egyptian equivalent of Tartarus, but atleast 3000 gods could march in there. Tartarus is 99.9% pure evil, so I doubt Carter can summon Horus or use his abilities.

Probably Percy would summon Carter if he found out about this common enemy which was discussed at the end of SoS.