Commercial Fixed Wing
Communication Breakdown
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Company Policy; Equipment / Tooling; Procedure
The Dispatch [program] alerted that a radio number was required to be added to [one of] my flights to avoid a conflict with the late arriving inbound flight of the same number. I complied with this by adding a suffix X to the call sign. What I was not aware of was that my counterpart on the sector next to me had also added a radio number suffix X to his flight with the same number based on the alerting from dispatch [program]. I was not advised in any messaging alert that this radio number was already in use. We ended up having two flights with the same radio number active at the same time on [the same] ATC frequencies.
A Dispatcher was notified of duplicate flight numbers by his company software program. To mitigate the problem; he added a letter suffix to the associated flight number; making it a radio number. He was not aware; that the Dispatcher responsible for the other flight had also received notification and added the identical letter suffix to his flight number; thus counteracting the mitigation.