Originally Posted by NewbieRunner

Oh dear! Z66 to C17 sounds like some of the worst connections I can think of. However, with a very few exceptions arrival and departure gates at FRA can change from day to day. I suggest you check the first post of the FRA connection thread in the LH forum (I have requested that your question should be moved there). C17 is an unusual gate for LH flights. May I ask where they are arriving from and departing to?

If their flight does arrive at Z66 if will take them 10+ mins to walk the Skyline train platform. They should take the Skyline train to B/C then it's another long walk to higher C gates. There will be transfer security on the way. There is really only one way to get there. The tunnel is in Schengen and does not help anyone going from Z to C.

If they have no mobility problem 1 hr 35 mins should be sufficient provided their incoming flight is not very late but they should expect to have to walk at least a mile or longer.