Originally Posted by
kg6rwo
It turns out that we may be transiting LHR for two separate trips. For one trip we will be going from T5C to T5A as described earlier. For the other trip we will be going from T5A to T3. It appears that the Heathrow express stop is in T5A level -2, the same level as we get off the Transit Train (or get up to from the walkway at level -4). Where do we clear immigration and security, in T5A or T3? Also, it seems that not all sources, i.e. Heathrow, talks about the Heathrow Express and only mentions the bus. Which one do you recommend?
OK, that needs a bit of untangling. You can't be 100% certain to arrive in T5C, even on an A380 arrival, it could go to a remote stand and then the bus from there would take you direct to T5A. Any other non domestic / Irish aircraft can in theory disembark at A, B or C. For T5A to T3, well the question will be are you airside or landside. If you come off a flight normally you would go via Flight Connections airside via a bus service that leaves from T5A and then visits T5B (but not C) and ends up in T3, and it is there that you pass via security, not in T5. There is no immigration if your final departure is outside the UK or Republic of Ireland. This is the fastest and best route, it is clearly signposted in purple.
If you decide to go landside, you then clear the UK Border (immigration) at T5, you then fully enter the United Kingdom and can go via any landside route to T3, the three main routes being the Heathrow Express (not acccessible when airside), the Tube (requires an Oyster or contactless payment card, Apple Pay, Android Pay) or the bus. HEX is probably best because the T3 station is closer than the tube, it's free and you need no ticket. The landside bus, which is separate from the airside bus is a public service bus, but free, I wouldn't recommend it due to the time it takes.