Pre-flight processing time needed for flight from Heathrow to US

the required 2 hours should be just fine.

Two hours will work if you're in the line at the desk, not just arriving and floundering around the terminal.

Ugh. Too bad your stuck with such an early flight.

Use the online check-in (available 24 hours before). You can ask the hotel to print out your boarding pass. That will save you from waiting in the check-in queue.

As noted in other posts here, and my own experience, LHR security is serious about one baggy of small carry-on liquids. Be sure to consolidate your stuff the night before.

Let me echo the idea that there is some serious security at Heathrow. I personally advise maybe giving yourself two and a half hours so you can go through the process without anxiety.

We always book a hotel at LHR the night before when departing early. There are lots of choices and price ranges. We check in around 1-3PM depending on where we stay and sometimes go out and leave luggage then return on the tube to London for a full day or a last night dinner. That takes the anxiety out of getting to LHR in the early morning. The Hoppa buses go to all the nearby hotels and deliver to all the terminals and start at 0430 each morning. Lots easier that way. Go to the London Heathrow website for more details.

Thanks for your replies, everyone. Isn't being there 3 hours early the recommended time to be there early for an international flight? Would two hours be enough?

It's a very busy place even for early flights. Lines at the ticket counters if you have to check luggage begin to form as soon as 0400. If you arrive at 0500 you will be clear back in line to check luggage. No luggage to check and have boarding pass in hand? Go directly to security since the lines are always daunting. There is no sense in not going early. LHR has lots of shops and eateries, some open around 0600 and you can sip a coffee and watch the international set walk by. Send me a PM and I can help you with LHR hotels we've used, if that's your plan.

I think you will find that United has very few early morning flights from Heathrow. If you check in online, at most you will have to drop off your bag and this does not take long. I've never experienced a super long queue for United at LHR.

As far as the security queue, I think you will also find that T2 (the terminal United uses) also has few early morning flights. At 5:30 am, there won't be hundreds of people in the queue.

I'd have no problem arriving at LHR T2 at 5:30am for a 7:30am flight if I had checked in online, but know others are more cautious.

Here are a couple more factors to consider in the mathematics. Most trans-Atlantic airlines carry out a second, and often more intense, security check at their departure gates. Also, airlines have grown insistent that passengers be sitting inside the plane at least a half-hour before the stated takeoff time. Arriving at the airport door two hours early seems a reasonably safe tactic.

The stated take off time can't have much to do with anything since it's not stated anywhere a pax would be able to find. The pilots know what it is since it goes into the fuel and speed calculations. Sure, you'd be tied in thirty minutes prior, but that half hour is going to be used up by push back, engine start, and taxi.

What a pax knows is departure and arrival times which are gate/door times -- what's printed on flight schedules and boarding passes.

If you had to board thirty minutes prior to the listed departure times, tight connections wouldn't work.

I'd think that the only way a flight would close the door early would be if every seat were booked and all seats were occupied. Even then, push back wouldn't come early since it'd screw up the gate schedule at the arrival airport -- or else burn up fuel on the tarmac once the huffers were pulled loose.

In a slow year I make at least a dozen trans-oceanic flights. As long as I hit the gate a minute before boarding pass departure time, I'm fat. If I can see the gate, it's past departure time, and there's still a throng moving about -- it's time to look for an expresso joint.