Date: 201704
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 5
Light: Daylight
Aircraft: A300
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Taxi
ATC / advisory: Ground ZZZ
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Training / Qualification; Situational Awareness
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Ground Excursion Runway
Detector: Person Flight Crew
When detected: Taxi
Result: General Flight Cancelled / Delayed
Contributing factors: Airport; Human Factors
Primary problem: Human Factors

Narrative: I was scheduled to operate [multiple flights]. Upon taxi out in ZZZ we were assigned by ATC to back taxi on [the] runway to perform 180 degree turn at the end for takeoff. This was due to taxiway closures and airport construction. My First Officer pointed out that they had just previously assigned the same clearance to an aircraft before us. Since taxiway A was part of the closures and since other aircraft were given the same clearance it led me to believe that I had no other option for departure. After we were clear of the ramp and positioned on the parallel taxiway I stopped the aircraft; set the parking break and we performed all briefings and pre-takeoff checks and checklists. I then handed my First Officer my iPad opened to the [procedures] and asked him to locate the description of the 180 degree maneuver so we could review it. I told him I had only done this maneuver once in my upgrade training in the SIM and I wanted to be sure that we would be doing it correctly. After review of the [procedure] we entered [the] runway at taxiway D and began to back taxi to the end of the runway. As I began the maneuver I solicited my First Officer's input since we had reviewed the procedure together. Both of us seemingly were in agreement throughout the maneuver. Just prior to beginning my hard over turn to the right my First Officer stated that he wouldn't go much further. I commented that I had not yet reached the runway edge but then began the right turn almost immediately thereafter. My First Officer was the first one to think that we were potentially off the runway. Since the aircraft seemed sluggish I boosted the power to see if it would continue its turn. It was at this point that it became obvious to me that he was correct. I then set the parking brake. We contacted the tower and notified them then contacted Operations. We started the APU then shutdown both engines. I contacted Operations to advise them of the situation. We remained with the aircraft until the decision was made to wait for recovery assistance. At that point we exited the aircraft and proceeded to the gateway. We submitted to the drug and alcohol test; contacted crew scheduling then went to the hotel until our scheduled jumpseat.  In hindsight I should have queried ATC about any other options for departure that would not require the back taxi. As we waited at the end of the runway for assistance I noticed the segment of taxiway between [two parallel runways] appeared to be open and usable. This would have meant that we could have back taxied made the right onto the taxiway and used [the parallel runway] for departure. Additionally; I believe that seeing and performing the maneuver on Operating Experience would have been helpful and should be incorporated into our training in the future.


Second narrative: [Report narrative contained no additional information.]


Synopsis: A300 flight crew reported a runway excursion when they attempted to do a 180 degree turn to position the aircraft for takeoff on a 150 foot wide runway.