Originally Posted by ISTFlyer

- Boarding in FRA starts 30 mins before departure for shorter flights and 40 mins before departure for longer flights so you would have time. However, depending on your specific departure date you might need to wait for the intra-terminal shuttle buses as the Skyline, which connects concourses is under maintenance, and it could take time.
- You don't need to clear passport control but security depends on the parking position of your incoming aircraft from LHR. If you type again, here on FlyerTalk with flight numbers on your travel date, members would be happy to help you with your specific transfer case.