AA 1866 then AA 4599 at Philadelphia
Denver → Philadelphia → Boston
Timetable, Philadelphia time
05:35AA 1866 from Denver at the gate
14:10AA 4599 to Boston leaves the gate
8 h 35 apart on the timetable
The last days
AA 1866 and AA 4599 weren’t both flown 15 min to 12 h apart in the last 21 days.
Statistics from past flights, not live flight information. Always check times and your connection with your airline, and don’t base travel or booking decisions on these numbers.