Narrative:

The event involved two aircraft sharing the same call sign at iad. One flight was holding for about 1 hour and there was another flight already in the air. Once I realized that there were two airplanes with the same call sign; I called washington center and informed them of the situation and they had me call cleveland center to also have them informed. After that I had a phone call not related to the situation; which could have waited; I was ready to ACARS the first flight; they had already taken off and I didn't want to contact them while they were in sterile cockpit. Since I couldn't reach the crew I contacted iad tower and they informed me that the other flight was diverting; and it appeared that there weren't any issues. Iad tower told me that they would check in with the flight. I'm not sure if washington center or iad tower was able to assist with correcting the situation. Cause; there were several factors that led to this event: 1. Low weather caused a flight to hold that had the same flight number as one on the ground. This caught me off guard since one flight would have been on the ground if there wasn't any holding. 2. My computer had an alert message and I didn't clear it out to see if there was another alert. Usually the alert box has alert messages for flight plans out of the country and in the early morning I have never had an alert for any flight conflict issues. The computer tends to catch these conflict issues for flights later in the day due to delays or aircraft swaps causing the call sign conflict. I've found that usually the computer sends an alert hours before a conflict becomes a problem. I think the computer didn't catch the problem due to the prolonged holding of the other flight. By the time I had cleared out the message the flight had already been out of the gate. 3. I think I could have handled the situation better by trying to contact the crew first instead of ATC. Since there was low visibility and other flights were diverting; I thought I had enough time to let ATC know and contact the crew. Also; I should have had the other phone call wait till I had taken fixed the ATC conflict. Response; once I realized that there was a problem; I immediately contacted washington center and called cleveland center at ZDC's request. I also called iad tower to let them know once I found out the flight was in the air.

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Original NASA ASRS Text

Title: Dispatcher described attempts to notify both ATC and Flight Crew personnel with regard to a same call sign issue brought about due to holding and late arrivals vs departures.

Narrative: The event involved two aircraft sharing the same call sign at IAD. One flight was holding for about 1 hour and there was another flight already in the air. Once I realized that there were two airplanes with the same call sign; I called Washington Center and informed them of the situation and they had me call Cleveland Center to also have them informed. After that I had a phone call not related to the situation; which could have waited; I was ready to ACARS the first flight; they had already taken off and I didn't want to contact them while they were in sterile cockpit. Since I couldn't reach the crew I contacted IAD Tower and they informed me that the other flight was diverting; and it appeared that there weren't any issues. IAD Tower told me that they would check in with the flight. I'm not sure if Washington Center or IAD Tower was able to assist with correcting the situation. Cause; there were several factors that led to this event: 1. Low weather caused a flight to hold that had the same flight number as one on the ground. This caught me off guard since one flight would have been on the ground if there wasn't any holding. 2. My computer had an alert message and I didn't clear it out to see if there was another alert. Usually the alert box has alert messages for flight plans out of the country and in the early morning I have never had an alert for any flight conflict issues. The computer tends to catch these conflict issues for flights later in the day due to delays or aircraft swaps causing the call sign conflict. I've found that usually the computer sends an alert hours before a conflict becomes a problem. I think the computer didn't catch the problem due to the prolonged holding of the other flight. By the time I had cleared out the message the flight had already been out of the gate. 3. I think I could have handled the situation better by trying to contact the crew first instead of ATC. Since there was low visibility and other flights were diverting; I thought I had enough time to let ATC know and contact the crew. Also; I should have had the other phone call wait till I had taken fixed the ATC conflict. Response; once I realized that there was a problem; I immediately contacted Washington Center and called Cleveland Center at ZDC's request. I also called IAD Tower to let them know once I found out the flight was in the air.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.