Flying from Pittsburgh to Rome, with a layover in Heathrow

You should have enough time, if not, they will still get you to Rome. At Heathrow, you will look for the "connecting flights" signs, the pathway even is color coded in purple, so just follow that. Do not follow the masses and go to immigration, you definitely do not have time for that.

You will not go through immigration, but there will be a security check. You can look here for more info: https://www.heathrow.com/connecting-flights

Make sure you check your terminals. It tends to get confusing with the partner flights. We flew from Seattle to Heathrow on AA/BA in July and went thru terminal 3. Either way you still need to go thru passport control and security (follow the signs) and then wait til they announce your gate a half hour or so before boarding. They do have buses to take connecting passengers to the different terminals if you need to change…. Again, just follow the signs.

If as you say, both of your flights are on British Airways, then you will arrive at terminal 5 and depart from terminal 5. (I checked.) Use the link given above by Paul to get step-by-step instructions.

No disrespect to Margie but her advice in your case is wrong.

You will NOT have to go through immigration/passport control or customs, but you will have to go through security again.

Just follow the "Flight Connection" signs and it will be simple. (Don't follow the crowd.)

You may have to change terminals when using the flight from Pittsburgh, even though both flights are on BA. I took the flight you're referring to and this was the case. We didn't pull up to a gate and were bussed to a terminal and then I had to make my way to another terminal. I had to pass through security, but not passport control. It took at least 90 minutes from the moment I landed to the time that I reached my gate. If this happens to you and you're running close, go to the front of the line and tell the personnel that your flight departs in ____ minutes.

90-minutes is enough time provided your flight departs on-time. After deplaning at LHR, check the board for connecting flights,. Heathrow is a major connecting hub for North American passengers so, it'll be you and a thousand others looking to move-on.

Upon landing you'll get herded though security for connecting passengers. Connecting flight security in UK is generally faster than off-the-street security. Terminal-5 is actually 3-buildings, the main bldg (you'll go through security and has all the amenities) is called 5A, the other two are 5B & 5C. On one trip I was returning to the US via LHR and flights were running late, there was a BA employee in uniform to greet me off my plane, and escorted me the entire way to my flight...up/down escalator, security, tram, all the way to the gate. :-)

Once completed, you'll be in the middle of the terminal with all manor of shops and places to eat. Check the board again, confirm which gate you need to get to, take a WC break, grab a unique British snack and enjoy the first step of your vacation. Get to your next gate with time to spare, upon landing at FCO you'll go through passport control then grab your checked bags.

I have done 90-minute connections and 75-minute connections with BA at Heathrow connecting going from SFO to Paris, Milan, Barcelona and couple of other cities. It's probably been 7 or 8 times. I have made the connecting flight every time. My luggage has made the connection once. Pack a change of clothes, or at least underwear, in your carry on bags. Actually, to be fair, on one trip to Paris with my family, 3 of the 4 pieces of luggage made the connection so let's say 2 out of 7 or 8 trips.

Thank you every one. You have been a lot of help.