A center controller and the crew of one of the aircraft involved; described the events leading up to...

Narrative:

Citation was cleared to FL180. [Air carrier X flight aab] was on course to [destination]. [Air carrier X flight aab] was NORDO for some period of time where sector 14 did not establish communications. I requested sector 14 start [air carrier X flight aab] down to get under citation. They informed me he was NORDO and could not comply. [Air carrier X flight acb] checked in also descending for [he destination]. I asked [air carrier X flight acb] to go through company and have [air carrier X flight aab] come to sector 15 frequency. Right after doing so; approach called and said [air carrier X flight aab] was on their frequency and I requested communications. [Air carrier X flight aab] checked in and asked if he missed a handoff somewhere. I informed him he did but it wasn't a problem and we would start him down soon. I called traffic to [air carrier X flight aab] and citation. My very next clearance was for [air carrier X flight acb] to cross 5 north of ZZZ VOR at 110 then reduce to 250k. [Air carrier X flight aab] read back [air carrier X flight acb] clearance and I missed that [air carrier X flight aab] read it back. [Thirty seconds later] [air carrier X flight aab] asked if I had traffic for him. I called the traffic again and issued an immediate 30 degree turn to the left. He never advised he received an RA. I asked if [air carrier X flight acb] got the clearance meant for him and he said affirmative.[suggest] have [air carrier company] eliminate similar sounding call signs aircraft landing/departing same airports.I did not tell [air carrier X flight aab] about [air carrier X flight acb]; but [air carrier X flight acb] was aware of [air carrier X flight aab] because I asked him to go through company to [air carrier X flight aab]on my frequency. I should have told [air carrier X flight aab] about [air carrier X flight acb] but due to him already coming on frequency late; calling merging target procedures to [air carrier X flight aab] and citation; and evaluating getting [air carrier X flight acb] down through overflight traffic at 110; I did not. I called traffic and a contributing factor to me missing the call sign readback was me assuming [air carrier X flight aab] wouldn't take a descent clearance immediately after I called traffic.

Original NASA ASRS Text

Title: A Center Controller and the crew of one of the aircraft involved; described the events leading up to the acceptance of a descent clearance for another company flight with a similar call sign. This resulted in a loss of separation with an opposite direction Citation.

Narrative: Citation was cleared to FL180. [Air Carrier X Flight AAB] was on course to [destination]. [Air Carrier X Flight AAB] was NORDO for some period of time where sector 14 did not establish communications. I requested sector 14 start [Air Carrier X Flight AAB] down to get under Citation. They informed me he was NORDO and could not comply. [Air Carrier X Flight ACB] checked in also descending for [he destination]. I asked [Air Carrier X Flight ACB] to go through company and have [Air Carrier X Flight AAB] come to sector 15 frequency. Right after doing so; Approach called and said [Air Carrier X Flight AAB] was on their frequency and I requested communications. [Air Carrier X Flight AAB] checked in and asked if he missed a handoff somewhere. I informed him he did but it wasn't a problem and we would start him down soon. I called traffic to [Air Carrier X Flight AAB] and Citation. My very next clearance was for [Air Carrier X Flight ACB] to cross 5 north of ZZZ VOR at 110 then reduce to 250k. [Air Carrier X Flight AAB] read back [Air Carrier X Flight ACB] clearance and I missed that [Air Carrier X Flight AAB] read it back. [Thirty seconds later] [Air Carrier X Flight AAB] asked if I had traffic for him. I called the traffic again and issued an immediate 30 degree turn to the left. He never advised he received an RA. I asked if [Air Carrier X Flight ACB] got the clearance meant for him and he said affirmative.[Suggest] have [Air Carrier company] eliminate similar sounding call signs aircraft landing/departing same airports.I did not tell [Air Carrier X Flight AAB] about [Air Carrier X Flight ACB]; but [Air Carrier X Flight ACB] was aware of [Air Carrier X Flight AAB] because I asked him to go through company to [Air Carrier X Flight AAB]on my frequency. I should have told [Air Carrier X Flight AAB] about [Air Carrier X Flight ACB] but due to him already coming on frequency late; calling merging target procedures to [Air Carrier X Flight AAB] and Citation; and evaluating getting [Air Carrier X Flight ACB] down through overflight traffic at 110; I did not. I called traffic and a contributing factor to me missing the call sign readback was me assuming [Air Carrier X Flight AAB] wouldn't take a descent clearance immediately after I called traffic.

Data retrieved from NASA's ASRS site 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.

Attributes
ACN	1358844
Time
Date	201605
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Aircraft 1
Make Model Name	Medium Large Transport
Flight Phase	Cruise
Flight Plan	IFR
Aircraft 2
Make Model Name	Cessna Citation Undifferentiated or Other Model
Flight Phase	Cruise
Flight Plan	IFR
Person 1
Function	Enroute
Person 2
Function	Pilot Flying First Officer Check Pilot
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict Deviation - Procedural Published Material / Policy

A center controller and the crew of one of the aircraft involved; described the events leading up to the acceptance of a descent clearance for another company flight with a similar call sign. This resulted in a loss of separation with an opposite direction citation.