Understanding Backtracking
 

One of the rules for the UA RTW is no backtracking. I understand this to mean that you can't go backwards. But what if the only *A route to your next destination requires a connection through a city you have already transited? Are you just out of luck? For example, if you want to go from DC to Prague, the SA website says take Lufthansa from IAD-FRA-PRA. But if you want to go from Prague to Athens, SA says take Lufthansa PRA-FRA-ATH. My question is, does the double connection through FRA violate the backtracking rules?

as far as I know, as long as you are in the max segments allowed, and you observe max stopovers, and other specific 'local' rules like not 'overshooting' the starting airport once you return, backtracking in the same continent (Europe, USA, Australia, Asia, Africa) is ok. I more often did backtracking in europe like Zürich - Vienna (east) than USA (and in the USA may be arriving from Europe in SFO, than back to the East coast, than via west coast to Asia or Australia).

I thought backtracking referred to IATA regions only? Maybe I am mistaken.

I believe that the OP is asking about the UA "Round the World" Promo, which has the following routing restrictions.

In this case, the rules state that no city may be transited more than once, so connecting in FRA twice is likely prohibited. A possible solution might be IAD-FRA-PRG and then PRG-VIE-ATH.

With the latter on Austrian of course.

Thanks for the suggestion about Vienna, I don't know how I missed that.