How do I manually view a seat chart on an American Airlines flight?

Never rely on a seat map as an indicator of upgrades or available space.

Replace the following placeholders with your flights details:

https://www.aa.com/seats/view?flightNumber=[NUMERIC_FLIGHT_NUMBER]&departureMonth=[NUMERIC_MONTH]&departureDay=[NUMERIC_DAY]&originAirport=[3_LETTER_IATA_DEPARTURE_AIRPORT_CODE]&destinationAirport=[3_LETTER_IATA_ARRIVAL_AIRPORT_CODE]

Example:

https://www.aa.com/seats/view?flightNumber=2739&departureMonth=4&departureDay=18&originAirport=MIA&destinationAirport=CUR