[AirlinesMustPay]

I am now enlightened as to what is being called an ATC problem. I had thought that the aircraft touched down on time, but congestion in the airport prevented it from reaching the gate. It is apparently something which prevents the aircraft from landing although they are hovering in the air ready to land.

Does that exonerate the airline? Absolutely not.

The passenger and the airline had a contract. She was to get into Philadelphia at a certain time and with enough time to catch a flight on another flight of the very same airline.

That can't be termed a "weather" problem which will provide the airline with an excuse, even if ATC slows down landing because of weather conditions. A weather problem that will excuse the airline is like if a flight is cancelled or delayed because of an approaching storm.

Parties to a contract are held liable if they do not perform. If the contract is frustrated by circumstances which they do not contemplate when the contract is made. They did not contemplate a storm on a particular day, so that is an excuse. If the air traffic controllers went on strike they also did not contemplate that.

However you say that that is the customary situation at Philadelphia. Even if it was because of visibility problem, it is the situation always to be contemplated by both the passengers and the airline if I understand both the OP and PHX correctly.

The airline must cater for that in planning their schedules. When their flight out of Philadelphia took off without the OP, they must have known that connecting passengers were on an arriving flight that was being delayed by ATC. They also must have expected such an occurrence since it is a regular occurrence. what they did was to make money on their seats by most likely selling them to stand by passengers. They could have held back the leaving flight until the passengers making the connection arrived. Its their decision and some would be inconvenienced either way. They chose to inconvenience those arriving, by allowing the leaving flight to leave on time. Long term they should plan schedules with longer times for connections. Again their decision.

As a passenger the OP need not get into all that. All her concern is, she did not make the connecting flight and there was no unusual occurence that frustrated the contract of carriage. If that was in Court, the airline has no sustainable argument that I could see.