Date: 202001
Location: ZZZ.Airport, US
Aircraft: Medium Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Takeoff / Launch
Airspace: Class E ZZZ
ATC / advisory: CTAF ZZZ
Second aircraft: Small Transport; Low Wing; 2 Turboprop Eng
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Communication Breakdown
Second reporter function: Captain
Anomaly: Conflict Ground Conflict; Critical; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Incursion Runway
Detector: Person Flight Crew
When detected: In-flight
Result: General None Reported / Taken
Contributing factors: Airport; Human Factors
Primary problem: Human Factors

Narrative: It is my opinion that we had made our departure CTAF broadcast at the same time as Aircraft Y and that caused us to not hear each other.  We had observed 3 different aircraft using Runway 17 (our inbound aircraft; a departing airline flight and an arriving airline flight) and elected to use 17 in effort to not disrupt flow of traffic.  Leaving ZZZ we taxied to RWY 17 from the terminal ramp making 2 CTAF calls en route; one for taxi and one for crossing 31/13.  At the end of the runway I called Center via phone to obtain clearance as stated by NOTAM and got clearance after confusion over call sign since ours was missing on our release paperwork.  After 15 minutes or so we were released by center.  I looked down the runway and saw no traffic and asked the Captain if he was ready.  He replied yes and I made a CTAF call saying 'ZZZ traffic; [Callsign]; departing Runway 17 with a right turnout; ZZZ' (the right turnout was misspoken).  We observed no traffic and had heard no radio calls from anyone other than an ops vehicle that appeared to be inspecting Runway 31 (does not intersect 17).  We waited for approximately 15 seconds before we took the runway as we completed the before takeoff checklist.  I once again called clear right while looking down the runway and observing no traffic.  On the roll I was given flight controls and advanced power.  As rotate was called I noticed a light on the departure end of the runway.  We took off normally and flew the ZZZ1 departure; and during initial climb I noted Aircraft Y on the 1000 foot markers for Runway 35.  At this point we heard a CTAF call from the aircraft but I do not recall the exact wording from the other aircraft.  We briefly communicated with the other aircraft before swapping to Center and continuing to ZZZ2.I believe us stepping on each others broadcast caused us to miss one another's departure call.  The departure end of 17 has buildings that made it somewhat more difficult to spot traffic and the sun was in our face towards the departure end of 17.


Second narrative: I believe that when we made our transmission before taking the runway we may have stepped on Aircraft Y making the same transmission at the other end of the runway. Due to that I don't think either of us heard the other aircraft. I chose to use Runway 17 due to the calm winds and that being the runway that every other aircraft had been using since we had been out on the airfield. I felt with other aircraft using Runway 17 it would be the least disruptive to the flow of the airport. In addition taking off on Runway 17 there was glare from the sun; and also a group of buildings off the departure end that helped hide Aircraft Y from sight.Departing ZZZ off of Runway 17; we had taxied to the end from the ramp. FO made two radio calls during the taxi; once for the initial taxi and then again when we crossed the intersecting Runway; 31/13. While holding short at the end of the runway I instructed the first officer to call Center via a phone number for clearance delivery out of ZZZ. There was some confusion over our flight number being filed as XXXA instead of XXX; as it wasn't in our remarks section of our paperwork and was only present in the ATC strip. We continued holding short of Runway 17 at the end for around 10-15 minutes while we double checked with dispatch and got our release from center. We were given our release and I asked the First Officer to double check the departure end was clear; I looked as much as I could and didn't see anything. He responded that it was clear and asked if I was ready. The first officer transmitted on COM2 on 122.80; as listed in the Lido charts; stating '[Callsign]; taking Runway 17 for departure; Right turn out.' We heard no responding traffic; took one more opportunity to look at both ends of the runway; and began to taxi out on to the runway after around 10 seconds or so. Upon alignment with the runway we again spotted no traffic on the runway; however there was a good amount of glare from the sun. I handed the first officer the controls and we began our takeoff roll. Right around Vr I noticed a light at the other end of the runway; and as we rotated I saw Aircraft Y pass well beneath us as they aborted their takeoff on Runway 35. He was around the 1;000 foot markers of Runway 35; and we were a good 500-1000 feet above him. The other aircraft made a CTAF call saying that we did not make any transmissions and they were aborting their takeoff. I responded that we had made multiple transmissions taxiing out to the runway; as well as another before taxiing onto the runway. He responded that he didn't hear anything we had said and that he was making radio calls as well. We continued with the departure and proceeded to Denver without further incident.I think that making more than one departure call would have helped negate this incident. Perhaps if we had made a '[Callsign] holding short Runway 17 ready for departure; any other traffic please advise' call before making our 'taking Runway 17 for departure' call it could have given the other aircraft more opportunity to hear and avoid us. The departing traffic was also VFR; so there was no separation provided from ATC; which would have helped but also we can't expect every aircraft to fly IFR all the time.


Synopsis: Air carrier flight crew reported that during the takeoff roll and initial climb; an aircraft attempted to depart from the opposite end runway. The other aircraft aborted the takeoff.