No customs or immigration for ATL
As mentioned by the others there is the skyline train that connects T1 and T2
. Check the gate for the CAI flight as soon as possible (maybe the crew can already ask for it). If the flight departs from Concourse A or B it's definetily best to take the train. When you get off just follow the signs for T1 A/B (to the right). you will walk along concourse D (depending on DL
's gate) towards concourse E. After the duty free shop (that's where local pax get through security) you will turn left and cross the check-in hall on a glass bridge. There's the station for the skyline train. this station is for transit pax only (as mentioned above there are two carriages; one for locals and one for transfers). There are two stops in T1. Where you hace to get off depends on your gate....
But there is also another possibility how to get to T1. This one you should only take if your LH
flight departs from Concourse C. In that case you just walk in the other direction (to the left) when you get off your plane. There should be signs for T1 C guiding you in that direction. T1 and T2
are connected. so you can walk from you arrival gate in concourse D to your departure gate in concourse C. But as I said, only walk if your gate is in C otherwise the skyline train is definitely faster.... to be honest I would only recommend to walk when you arrive at a gate between D9 and D13.
But if you follow the signs there should be no problems at all. the minimum departure time for FRA
is 45min , so you shoul make it... (as long as your DL
flight is on time, of course
I hope my explanations were not too confusing for you!!!!
Enjoy your flight and have some good 55min in FRA