Originally Posted by GregL

If you are looking at today's flight, it appears that you were originally supposed to use the aircraft that flew CLT-TRI-CLT as AA4885, but that flight went mechanical in TRI with an estimated 4pm departure.

As a result, at 1pm ET, they swapped aircraft to use a plane that was due in from FAY at 1:25pm (AA4856).

You really need to use a variety of sources to determine this.

Flightstats.com gives a history of time changes and aircraft assignments / swaps.

Flightaware.com will tell you where an aircraft is at the current moment.

Expertflyer.com will give you a reason for the delay.