Originally Posted by
chreesbed
I guess my BP should not be flagged as not ready to fly as I will use it to clear transit security at T5 once I have transferred there. Or am I wrong in this assumption and I should fix it somehow?
You won't have an issue with Ready to Fly, since that's only once you get to T5. The problems there relate to people leaving T5 and then returning, but that doesn't apply to you.
You can go via Flight Connections T3 to get to the T3 lounges, however there is a security check and before that your boarding pass won't scan properly. You can then tell the security agent that you wish to use the T3 lounges - this is permitted but some agents will simply assume you have misunderstood LHR's layout and send you to T5. Other agents won't be impressed that you are going through security twice unnecessarily when staff are fully stretched. Assuming you get through this you can go to the lounges, then allowing perhaps 2 hours you go to T5 via Flight Connections again - there are signs in the vicinity of the AA lounge. That's a bus and then another security scan. Add that all up together and it's a lot of flapping around, so you are frankly better off going to T5 directly, though using the AA Arrivals lounge (which is landside) is a good idea too.
It's much better to save this T3 experience for a future visit when actually departing from T3. Good though the lounges are in T3 it isn't a life changing experience.