B767-300 and 300 ER
Dispatch Dispatcher
Confusion; Situational Awareness
Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Flight Crew FLC complied w / Automation / Advisory
ATC Equipment / Nav Facility / Buildings; Human Factors
Aircraft X for Day X was delayed into [the next day; Day X+1]. [Another flight; Aircraft Y; using the same call sign was] operating on time [on Day X+1]. Both flights were in the air at the same time and would both be in ZZZ Center at the same time. (Actually both flights would have been line of sight with each other just north of ZZZZZ VORTAC.) Dispatcher noted this just after takeoff for Aircraft X. ATC Coordinator was notified who in turn contacted ZZZ Center. A temporary call sign was assigned to the eastbound flight for crossing ZZZ airspace. Dispatch notified both flights of the situation and remedial action; and of the similarity between [the two] calls signs.Long delay of twenty hours caused overlap in date change flights. Do not delay flights into the next day without setting up as extra section or by stubbing immediately upon determining the length of the delay.
Dispatcher reported a long delay caused two flights with identical call signs to be in the air at the same time.