slizer
In normal segregated operations there is no requirement for ATC to wait for one aircraft to land before clearing another for take off.
Dependent operations, however, which do require the arrival to be either more than 2 miles from touchdown or landed, prior to rolling the departure are used when the standard missed approach cannot be flown for whatever reason, or an ILS approach is not flown or other less common reasons I will not go into here.
j17
You're almost right, its KPHL - Philadelphia.