Date: 201510
Local time of day: 1801-2400
Location: ZJX.ARTCC, FL
Flight conditions: VMC
Light: Night
Aircraft: A319
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class A ZJX
ATC / advisory: Center ZJX
Reporter organization: Government
Reporter function: Enroute
Human factors: Communication Breakdown
Second reporter function: Captain; Pilot Flying
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: I was working R76 as the Radar and issued the A319 at FL380 a clearance direct FILBE and cross 20 miles north of FILBE at FL360. The pilot read back all of it and then stopped and said repeat the altitude. So I reissued the whole clearance again very slowly. The pilot read back the entire clearance with his call sign with the correct altitude of FL360. However 5 mins later a B737 level at FL350 was converging within 3-5 miles with the A319. A merging target call was not required based on the targets. So the A319 vacated FL380 to meet his crossing restriction. He continued descending beyond FL360 and the next controller questioned the pilot and he stated he had worked it out with me and that I had given him FL260. But this is incorrect as I reviewed the audio tapes. The relieving controller amended the altitude to FL340 and coordinated with R58 St. Augustine. The Loss of Separation was 4.9 miles and 600 feet. This was a pilot deviation. No further issues occurred.The relieving controller could have issued a merging target call even though the targets did not merge. But an added safety net when aircraft are within 3-5 miles and descending or climbing is a good practice.


Second narrative: I was the pilot flying and I believe Atlanta center (May have been JAX Center) gave a clearance to my flight to cross 20 miles north of FILBE intersection at what we thought the controller said FL260. The first officer asked the distance and altitude to confirm and again we understood 20 miles north of FILBE intersection on the FRWAY5 arrival at FL260. So I made the appropriate changes to the navigation system and entered 260 into the altitude selector and the first officer confirmed the altitude and then I managed the descent. The controller was cordial and handed us off to a JAX center frequency. The new controller asked us what our clearance was as we were descending through FL350. We responded to cross 20 miles North of FILBE intersection at FL260. He instructed us to level off at FL340. Which we did. A few seconds later he told us the clearance was to cross at FL360. 'Just so you know' Is what he told us. We told him we read back and confirmed the altitude with the previous controller. No other communication occurred concerning the misunderstanding and we were handed off to the next controller. No other inquiry was made by the controller.Somewhere in the communication process there was a misunderstanding between instructions. As the flying crew we followed company and FAA procedures to comply with the instructions. In fact the radio was fairly quiet that night and I believe we heard the instructions correctly and backed each other up. At no time was I being overwhelmed with tasks; it was a routine and pleasant flight. Company policy has always been very good concerning this type of event. We double check the altitude cleared to and then double check with each other that it is loaded correctly into the Navigation system. Then double check between each other that the procedure is actually executing correctly. I believe that the flight was conducted with the highest degree of safety and company and FAA policies.Seems to me the only way this could have happened was just a simple misunderstanding of the FL cleared to. We heard FL260 twice. From now on I will strive to repeat the leaving altitude and target altitude to the controllers as a way to triple check the correct clearance.


Synopsis: A319 flight crew and the Controller involved describe a misunderstanding of a crossing restriction assignment; even after the controller repeated it twice.