I have 90 minutes to change planes at London Heathrow terminal 5. San Diego flight on British Air connecting to a BA flight to Madrid. Is this enough time?

Should be fine. Your bags will be checked through. I assume they are one booking. If so, even if your arrival is delayed and you miss the connection, they'll put you on the next available flight.

You need to ask BA if you will have to clear Customs and Immigration in the UK or in Madrid.

While it may be possible to make the connection even if you have to clear Customs & Immigration in Heathrow, any hold-up- or flight delay will make it very tight.

Getting put on the next available flight may not be convenient if the next 'available' flight is the following day. I would not want to count on a 90 minute connection if your bags are not checked through and Customs & Immigration had to be done in the UK. Even departing a half hour late from San Diego could see you missing the connection.

Check with BA to find out where you will clear Customs & Immigration and/or if your bags will be checked through. I never ASSUME anything when it comes to air travel.

You are only connecting through LHR. You are NOT entering the UK. You will not go through UK. Immigration. You will go through security.

This is a very simple connection.

Plenty of time!

Thanks all. Looks like we'll make it, if not, we'll be spending the night as the next flight is the next day.

You do have plenty of time but one caveat sometimes you need to get the monorail between gates, so I would make my way immediately to your next gate just in case of hold ups!

We had allowed 3+ hours between our flight from EWR to LHR and our flight to Kenya last summer. A thunderstorm delayed our departure so that we had very little time to make our connection. Fortunately, we were met at the gate by a BA employee, handed a card to expedite going through security and told exactly how to get to our gate. I was impressed.

If you are experiencing delays, or it looks like your flight is running late, I'd suggest contacting the Flight Attendant and requesting assistance with the connection. They should be able to at least get things prepared on the ground (although they likely know which passengers are running late or have missed connections and advise accordingly) or let you know your options.