With two aircraft with similar call signs on opposite direction paths; the wrong aircraft accepts a descent clearance resulting in a traffic conflict and confusion.
Synopsis
With two aircraft with similar call signs on opposite direction paths; the wrong aircraft accepts a descent clearance resulting in a traffic conflict and confusion.
Narrative
ZZZ was IFR and numerous aircraft were awaiting clearance to depart as well as ACR XXXY inbound to ZZZ. I was on and off the frequency to expedite the flow of traffic in and out of the ZZZ airport. When the R-side was issuing the descent clearance to ACR XXXX I was checking another departure out of ZZZ to make sure I had the spacing needed to give another release to depart to help the R-side reduce the delay on ACR XXXX inbound. I was looking at this when descent clearance was given and did not hear the readback that ACR XXXY had read it back instead. While I was giving the release to ACR ABCD is when I heard the R-side give a traffic alert to both aircraft and realized the incident occurred. We do get many ACR XXXY and ACR XXXX going back and forth between ZZZ and LAS on exact opposite courses which seems dangerous on the similar sounding call signs. Both aircraft are usually descended within the same vicinity also. My recommendation would be not to have the similar sounding call signs used between ZZZ and LAS with both aircraft going to be on the same frequency the majority of their flight.
Second reporter narrative
As non-revenue repo flight XXXY (LAS-ZZZ); we were approximately half-way to ZZZ in cruise at 15;000 when we heard the controller issue a descent to 9;000. At the same time we were overhearing instructions from our controller to ACR XXXX (ZZZ-LAS). Shortly after beginning descent; we observed an opposite-direction TCAS target 1;000 FT lower and straight ahead; closing. The controller then quickly issued several instructions to both of us. One; to expedite descent and for the other to maintain altitude. I believe that two flight numbers were transposed more than once. Now; in hindsight; it's easy to know which ATC instructions were intended for which aircraft. Then; I believe that the controller was issuing correct instructions but using incorrect call signs i.e. ACR XXXY when it should have been ACR XXXX and also vice-versa. The situation was briefly very confusing for all concerned but; noting traffic lower and dead ahead; it was clear we needed to return to 15;000 and did so from around 14;200. Company traffic; ACR XXXX; continued descent. We passed with no more than two miles horizontal separation and 2;000 FT vertical separation. Both the First Officer (FO) and I were certain we had heard (and read back) instructions to descend using our flight number. I can't recall if the FO was off-frequency during the initial instruction or not; but he was on frequency for all subsequent transmissions. After several minutes; while were commencing approach; the controller issued us a phone number to call and I did contact ZLA after landing. The ZLA person recapped their version of the event which had us as taking the descent clearance intended for the other aircraft to descend to 9;000. If the tapes confirm that; then we both mis-heard the instruction for a similar-sounding flight number. Our readback there went uncorrected; and this fact was mentioned by the ZLA person too. Afterwards; we continued our approach to ZZZ which was reporting MVFR conditions due to ceiling. The Controller issued a much delayed approach clearance which prevented us from descending sufficiently. We were too high upon breakout on the first approach and had to go around. The second approach was successful. I was urged during the phone call to use my company channels to have these two similar sounding flight numbers (XXXX and XXXY) changed and I have submitted an appropriate company report for that purpose.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.