Date: 202107
Local time of day: 1201-1800
Location: ZLA.ARTCC, CA
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class A ZLA
ATC / advisory: Center ZZZ
Second aircraft: Commercial Fixed Wing
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting; Communication Breakdown
Second reporter function: First Officer; Pilot Flying
Anomaly: Conflict NMAC; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Automation Aircraft TA; Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: ATC Equipment / Nav Facility / Buildings; Chart Or Publication; Procedure; Human Factors; Environment - Non Weather Related
Primary problem: Ambiguous

Narrative: Original clearance was to fly the ORKA5 departure with LAS transition. FO was flying. At or near COOPP intersection Center gave us instructions that we understood to be 'fly heading 070 degrees and expect ORCKA and then the BEALE transition'. We set up our FMS for this new transition. Shortly afterward we both heard what we thought was 'cleared direct ORCKA and fly the BEALE transition' and the CA read exactly that back.  A few minutes after we had established course to ORCKA center called another flight and directed a stop climb at FL190. We were passing through FL200 for FL230 when we noticed another aircraft on TCAS at 10-15 miles range reach 300 feet below our altitude before descending back down to FL 190. Center then called out that we were off course. CA replied we were direct ORCKA then BEALE Transition as directed. Controller then stated 'No you were cleared ARCUS and the BEALE transition'. ARCUS is the next fix after ORCKA on the ORKA5/BEALE SID and sounds very similar to ORCKA on a VHF radio. No TCAS alerts were initiated and no conflict occurred.The primary factor is the fact that ORCKA and ARCUS; two consecutive points along the ORKA5 SID sound similar over the VHF radio.  So similar; in fact; that both pilots heard it wrong when the clearance was first issued and the ATC controller heard it wrong when we read it back.Two suggestions: 1. I recommend that Jeppesen change either ORCKA or ARCUS naming on the SID.  2. When waypoints on a SID sound so clearly similar ATC should phonetically spell out the fix cleared to.


Second narrative: Original clearance was to fly to ORKA5 departure with LAS transition. FO was flying. At or near COOPP intersection Center gave us instructions that we understood to be fly heading 070 degrees and expect ORCKA and then the BEALE transition. We set up our FMS for this new transition. Shortly afterward we both heard what we thought was cleared direct ORCKA an fly the BEALE transition and the CA read exactly that back. A few minutes after we had established course to ORCKA center called another flight and directed a stop climb at FL190. We were passing through FL200 for FL230 when noticed another aircraft on TCAS at 10-15 miles ranger each 300 feet below our altitude before descending back down to FL190 LA Center then called out that we were off course. CA replied we were direct ORCKA then BEALE Transition as directed.Controller then stated ' No you were cleared ARCUS and the BEALE transition. ARCUS is the next fix after ORCKA on the ORKA5/BEALE SID and sounds very similar to ORCKA on a VHF radio. No TCAS alerts were initiated and no conflict occurred.The primary factor is the fact that ORCKA and ARCUS; two consecutive points along the ORKA5 SID sound similar over the VHF radio. So similar; in fact that both pilots heard it wrong when the clearance was first issued and the ATC controller heard it wrong when we read it back.Maybe a change to the fixes on the SID.


Synopsis: Air Carrier pilots reported two similar sounding waypoints on this SID which caused a heading deviation and TCAS traffic warning.