Date: 201512
Local time of day: 1801-2400
Location: ZID.ARTCC, IN
Light: Night
Aircraft: Light Transport; Low Wing; 2 Turbojet Eng
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Climb
Airspace: Class E ZID
ATC / advisory: Center ZID
Second aircraft: Light Transport; Low Wing; 2 Turbojet Eng
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Communication Breakdown; Situational Awareness
Anomaly: ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
Result: Air Traffic Control Separated Traffic; Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: Aircraft X was departing eastbound. After I took the handoff I noticed the aircraft climbing above 10000 feet which is the top of TRACON airspace. I called TRACON to ask if they were still talking to him and what altitude he was climbing to because I was not talking to him. They said they said they assumed when he climbed he was talking to us and we had given the aircraft a climb clearance. I then asked them to see if maybe he was still on their frequency. A few moments later they called me back and said he was switching over to me and asked me to question the pilot why he didn't stop at 10000 feet.I then issued Aircraft Y a 30 degree left turn for upcoming climb. I heard a read back of roger turning 30 degrees left and thought it was Aircraft Y because that was who I was expecting to read it back and did not focus on the call sign. A few moments later Aircraft Y asked me if the turn was for them and I said yes. Aircraft Y then informed me that they did not get the clearance and that someone else had read it back. I then asked Aircraft X did you take the 30 degree left turn and they said yes. I told the pilot that was not for them and then issued Aircraft X direct routing and climb and maintain 23000 feet. I went back and issued the turn to Aircraft Y. A few moments later I then asked Aircraft X why they climbed to 13000 feet and didn't stop at 10000 feet. They said that was what they were issued by TRACON. I then reported it to the controller in charge that we may have a pilot deviation. I called TRACON to let them know the pilot told me that he was assigned 13000 feet. The controller told me that the supervisor was listening to the tapes. Before I switched the aircraft I read them the brasher statement. When I went to switch Aircraft Y a few minutes later I thanked them for questioning the situation to make sure the correct aircraft got the clearance. They then informed me that when I was giving them the vector clearance they heard Aircraft X checking in on the frequency and that we had stepped on each other. I told them I couldn't hear that on my end and thanked them again and switched them.Communication is the biggest factor in my opinion on this situation. Readback hearback issues continue to be one of the hardest human factors to figure out how to mitigate. I think that the largest limiting factor in air traffic control is our radio system. The fact we are still using a party line radio system both limits the volume I can work and adds to confusion. I know going to some type of a direct link radio system would be a bigger task than RVSM was (I am a former avionics engineer; and commercial pilot; so I understand the magnitude of that change). Until this happens I would really like to see the FAA make a large public announcement campaign to pilots and controllers about using their full call signs and if they are NORDO for more than 5-10 minutes to use 121.5 to get on the correct frequency. Something similar to the 'line up and wait' campaign. I think if we really make a push for information sharing on that level that could help. I know I have pilots daily take control clearances or frequency changes without using a callsign at all.




Synopsis: An aircraft passed through a previously assigned altitude of 10000 feet while not in contact with the ARTCC who controls the airspace. Furthering the incident; once in contact with ATC the aircraft then accepted a clearance that was intended for someone else.