Madrid vs Lisbon airports

On a USA - LHR - LIS/MAD - OPO itinerary, as you guessed, you will have to clear passport control in Lisbon or Madrid, regardless of which one you choose.

I believe at MAD you will also have to clear security but I'm not 100% sure on this, so will leave to others to comment. No idea on LIS.

Do you have to fly from Heathrow? TAP has direct flights from Gatwick to Porto.

Edit: Missed the fact that you're arriving at Heathrow. That complicates things. And to be frank, if the plan is to travel to Porto, booking a flight to Heathrow is a pretty bad idea imo. In theory, Iberia should be the better choice as they are also in Oneworld and there should be a theoretical, albeit small, chance that you might be able to connect the bookings.

At MAD you would go through immigration, take a people mover to the other part of the terminal, and then clear transfer security before an intra-schengen flight. (wait time for immigration can be a crap shoot—I'm usually through quickly, but have waited 40 minutes. Very short/no lines for that security)

Thank you all for your responses.

Regarding my choice of fights: I scheduled the flight to Europe last year using the remainder of my American miles. i was able to get two business tickets - but only to LHR. When i booked there was an early morning non-stop flight from LHR to OPO, it has been cancelled. i kept hoping some airline would add a non-stop out of LHR, but ....

We could go to Gatwick and get a non-stop the next morning, but not till 10:15 - and that wastes a lot of the day. I think i will "bite the bullet", "roll the dice" and try the same day flight, probably through Madrid. Looks like that flight lands in T4 and we depart from T4s
for Iberian on to OPO. With luck it is doable. if not, we spend some time in Madrid!

again, thanks for help.

When i booked there was an early morning non-stop flight from LHR to
OPO, it has been cancelled. i kept hoping some airline would add a
non-stop out of LHR, but ....

That flight is summer only. The chance of any airline adding a flight in November is more or less zero. Heathrow operates at more or less full capacity and the slots are very valuable, so airlines will use them for the most profitable

We could go to Gatwick and get a non-stop the next morning, but not
till 10:15 - and that wastes a lot of the day. I think i will "bite
the bullet", "roll the dice" and try the same day flight, probably
through Madrid. Looks like that flight lands in T4 and we depart from
T4s for Iberian on to OPO. With luck it is doable. if not, we spend
some time in Madrid!

You could also spend a day in London, which is not really wasting time. Self connecting at Heahtrow on the other hand takes some time. When do you land and when do the flights to Porto depart?

We land at 11:50am at Heathrow on 11/15. We have gotten conflicting info about which terminal American lands in, terminal 3 or 5.

The flight through Madrid leaves at 2:50pm. Not sure which terminal as the first leg of the trip is on British, - then Iberian from Madrid to Porto.

It is inconvenient, but we saved a bunch being able to use miles, so i can't complain.

Susan,

Your AA arrival at LRH will be in Terminal 3. All BA and Iberia departures to Madrid leave from T5. Others here know the 3-to-5 transfer better than I do, but I think 3 hours would be plenty IF you aren't checking bags or if the AA agent at your origin manages to check your bag all the way to OPO (they should be able to, but if they have the willingness or training can be a crapshoot.) If you have to claim bags, change terminal, and re-check it might be a different story.

Edit to add: Small correction: At MAD, your arrival from LHR will be in T4S; the departure to OPO would be from T4. (I maintain that in the US, we would not call them separate terminals, but different concourses of the same terminal.)

Three hours for self connecting at Heathrow is too optimistic for my preferences. When does the TAP flight depart?

Flight on TAP is earlier i am afraid.

There are options out of Stansted Airport, i had not heard of that airport until i started hunting for options. It seems to be about 1hr 20min by taxi. i don't think there are any really good options.

STANSTED
on November 15, 18:00 nonstop to Porto on RyanAir
Or on November 16, 8:15am nonstop on Ryan

thanks again for help

In that case I would not book a flight from Heathrow to Porto the same day. It seems a bit risky to me. But maybe you don't mind a bit of risk? If you're booking the Iberia flight, make sure you have a plan B though because there is a risk that you miss the flight. And while airlines sometimes can wait for you, they don't wait at Heathrow.

i don't think there are any really good options.

As I said, if the plan is to travel to Porto, booking a flight to Heathrow is not a great idea…

There are direct coaches from Heathrow to Stansted that take around 1:20 to 2 hours, depending on departure time. So really no need to take a taxi. And there is always the risk of traffic on the M25 so you need a bit of margin. If it was my trip I would probably either spend the night in London and take the TAP flight to Porto from Gatwick the next day, or take a flight from Heathrow to Lisbon later the same day and spend the night there.