Details of the reason for the grounding of this are emerging. Someone is reported to have made a call to a local police authority mentioning this flight, the call was enough to provoke a response.
Flight due to take off at 0730 local - Flight AA24, it never took off & has been parked since 0845 local on the bay side of the airport. In 10 minutes there will be a media briefing.
AA has said this is not a terrorist situation & other flights (inc AA) are landing & departing SFO fine.