Originally Posted by
orbitmic
You can’t access t5 departures when your flight is from t3 so the answer to q2 is no. The answer to q1 should be no too but you might get lucky (unlikely).
I have been able to access T3 with a T5 departure. Had an 8-hour layover due to a schedule change and the agent let us in to use lounges. So they can do it.
T5 seems more strict, though, so I'd expect it to be less likely there than at T3.
Cheers.