Date: 201701
Local time of day: 0001-0600
Location: CLT.Airport, NC
Flight conditions: IMC
Weather elements / visibility: Rain
Light: Night
Aircraft: Large Transport
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
Airspace: Class B CLT
ATC / advisory: TRACON CLT
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Situational Awareness
Second reporter function: Pilot Flying; First Officer
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Other / Unknown
Detector: Person Air Traffic Control
When detected: In-flight
Result: Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Aircraft; Procedure; Human Factors
Primary problem: Procedure

Narrative: After push back and start we were issued taxi instructions to 18C; then switched to tower; given an initial heading of 190 degrees and cleared for takeoff. Shortly after takeoff I; as the Pilot Monitoring; contacted departure and complied with their heading vector of 240. The controller then gave us a phone number to call as soon as we landed regarding a possible pilot deviation. The rest of the flight to [destination] was uneventful; no one said anything to us further about pilot deviations. In [destination airport]; after completion of the shutdown checklist and all passengers had deplaned I called the number given to us.The fellow who I spoke with identified himself as a supervisor at CLT approach. He stated that we had violated a waiver that CLT operates under during inclement weather which requires simultaneously departing aircraft from 18L and 18C to remain with tower until a 15 degree divergent vector can be given and then switched to departure control. The departure instructions we had received prior to take off was to fly heading 190 which we did until I contacted departure control shortly after takeoff who then instructed us to fly heading 240. [The supervisor] stated that the violation was created when I switched to Departure Control before tower gave us the vector. [The supervisor] stated that they have 'ticks' at about 1.8 miles and the divergent vector needs to be given by tower and then; once established on that heading tower switches us to departure. I asked [the supervisor] if there was any guidance for me regarding this waiver and the associated procedures. He said he was unaware of any written 'on the charts'. I asked [him] if we had caused a conflict with the other aircraft departing Runway 18L and he said he didn't know; but his quality assurance team would be looking at the data to determine our spatial relationship with the other aircraft that was departing off of Runway 18L and would make a note to have someone call me. I was unaware of the requirement to stay with tower until they issued a turn and then switch to departure control.After takeoff; if tower doesn't switch me to Departure Control ask tower if they want me to switch. ATC should publish this departure procedure so aircrew are aware of it.


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


Synopsis: Air carrier Captain reported he did not realize they were supposed to wait for frequency change instructions. They switched from Tower to Departure Control on their own.