B777 Undifferentiated or Other Model
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 11.0
Confusion; Situational Awareness; Communication Breakdown
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic; Flight Crew Requested ATC Assistance / Clarification
Human Factors; Procedure; Company Policy
When Aircraft X checked on at 340 he asked for higher. I told him he had traffic overhead but would diverge in about 40-50 miles and I would get him 360 when it was available. Aircraft Y has also had a request for higher and I couldn't give it at the time. Later Aircraft X asked again and said would be willing to turn if necessary. I was looking right at Aircraft Y and remembered he had asked earlier. I had additional crossing traffic for him at 360 and asked if he could accept 380. He said he could and I climbed Aircraft Y to flight level 380 and changed the data block to reflect that. I didn't realize that both Aircraft Y and Aircraft X were on frequency and while I thought the second request came from Aircraft Y it was in fact Aircraft X I was talking to. So when I climbed Aircraft Y; it was Aircraft X who responded to the climb clearance and I didn't catch it. I didn't realize I had the similar call signs until the conflict alert went off. Initially I thought it was a Mode C swap and then I realized what had happened. At that point; I had already lost separation but both aircraft were diverging and Aircraft X was almost above Aircraft Z with his high climb rate. So I turned them both just to provide some extra space.Always make sure to use call signs with every transmission. To the extent possible; do not schedule two flights with nearly identical call signs; to be on the same route at the same time.
While at FL340 the ride was moderate chop and we queried ATC about the rides higher which were better. We requested FL360 and the Controller asked us if we could do FL380 which we could do. He then gave us a climb to 380. We started climbing; and then the Controller asked us what altitude we were cleared to and then gave us a right 20 degree turn and re cleared us to 380. There was an airplane behind and to the left at 360 which also got turned. The Controller then said there was a [Company] flight and that there was some call sign confusion.
ZDC Controller and B777 First Officer reported the wrong aircraft accepted a climb clearance due to similar sounding call signs.