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Join Date: Sep 2009
Location: Minneapolis: DL DM charter 2.3MM
Programs: A3*Gold, SPG Plat, HyattDiamond, MarriottPP, LHW exAccess, ICI, Raffles Amb, NW PE MM, TWA Gold MM
Posts: 102,617
My understanding is that the 70 pound limit is for employee safety. Heavier bags can fly as cargo, but this would be a hassle for the passenger.
If you check in with DL, I would expect bags to be charged by DL following KE rules if there aren't DL segments on the ticket/PNR.