On a recent trip to San Francisco I had a window seat and the ability to leave my cell phone during the landing. This allowed me to document something that I would not even know was happening if I had an aisle seat. As we flew over San Francisco Bay approaching San Francisco International Airport, I saw a Southwest airplane paralleling us. It slowed and fell behind and below us.
We ended up flying directly over the airport instead of landing. I suspect that the Southwest flight was told to go first and we told to circle around for another pass. The photo below shows the airport as we flew over.
We ended up going all the way to the Pacific Ocean before turning around. It is not that far so it did not take long in a plane. Here is a shot as we approach the airport from the opposite direction.