Date: 202106
Local time of day: 1201-1800
Location: LAS.TRACON, NV
Light: Daylight
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
ATC / advisory: TRACON L30
Second aircraft: Commercial Fixed Wing
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Training / Qualification; Confusion; Communication Breakdown
Anomaly: Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Automation Air Traffic Control; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented
Contributing factors: Procedure; Chart Or Publication; Human Factors
Primary problem: Human Factors

Narrative: As PM; the Captain and I were nearing BERBN intersection on the COKTL 1 Arrival into LAS. After receiving the ATIS for LAS; and before beginning the descent on the COKTL 1 Arrival; the Captain briefed the COKTL 1 Arrival; along with the visual approach; backed up with the ILS to Runway 26L. Conditions at the time were VMC DAY (15;000' few/10SM vis). Prior to reaching BERBN intersection; Approach Control asked us if we had the ILS loaded. I looked over to the Captain and we both nodded; at which time I stated that we did indeed have the ILS 26L LAS loaded into the FMC (from the direction of PRINO intersection). The Approach Controller cleared us to fly the ILS 26L with a clearance to cross BERBN at or above 7;000 feet MSL. I then queried the Approach Controller about whether or not they would like me to call our base leg for Runway 26L.  The Controller replied that our base leg would be visible on their radar; and that a call was not necessary. Not realizing that there was INDEED a transition from the BERBN intersection to HUXAR on the ILS 26L; we proceeded turn north whilst descending to intercept the Runway 26L localizer just outside of RELIN intersection (D7.2 IRLE) Runway 26L.Shortly thereafter; we were told by the Approach Controller that we had initiated the turn too soon; and we were given a heading to the East in order to avoid traffic (other carrier) that was already established on final for Runway 26L.  We did receive a TCAS TA (no RA); and after completing the turn to the East; the TCAS TA was resolved. After the turn to the East; and with proper separation between our aircraft and Aircraft Y; Approach Control vectored us back to the north to join the localizer and clear us for the visual to LAS Runway 26L. We were then handed-off to LAS Tower. Landing was uneventful. After landing; we were provided a phone number to call LAS TRACON. The COKTL 1 Arrival and the latest ILS 26L charts for LAS are dated (date). I can tell you that I was certainly not familiar; nor had I ever been assigned the ILS 26L from the COKTL 1 Approach (I wasn't even aware that there was a transition from BERBN intersection; as that transition is located on the new ILS 26L Approach chart). My apologies to the LAS Approach Controller for our misunderstanding.As an added measure; I would prefer to see more information added to the COKTL 1 Arrival; like a ball note referring Pilots to the BERBN transition on the ILS 26L LAS.  An added note within our company pages may help bring attention to this transition as well.




Synopsis: Air Carrier First Officer reported a heading deviation caused by a new and unfamiliar approach procedure for LAS airport.