My recollection is that, when PanAm sold some select routes to UA (and I think it was around 90 or 91), the FF programs were linked. I don't recall a mileage transfer option, but you could definitely use Pan Am miles for UA awards (I had an F trip to Asia that way); however, some time after Pan Am filed for bankruptcy, UA first made it very difficult and then impossible to use Pan Am-issued UA tickets. As part of the deal with DL under which DL was supposed to get the remaining Pan Am routes, I think any remaining FF miles were to be transferred to DL FF accounts.