Date: 201707
Local time of day: 0601-1200
Location: ZDV.ARTCC, CO
Flight conditions: VMC
Light: Daylight
Aircraft: Small Transport
Operator: FBO
Operating under: Part 91
Flight plan: VFR
Mission: Skydiving
Flight phase: Climb
Airspace: Class E ZDV
ATC / advisory: Center ZDV
Second aircraft: Small Aircraft; High Wing; 1 Eng; Fixed Gear
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness; Communication Breakdown
Anomaly: ATC Issue All Types; Conflict NMAC; Deviation / Discrepancy - Procedural Clearance
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Company Policy; Human Factors; Procedure
Primary problem: Procedure

Narrative: I was working the radar controller position. This particular airspace goes from the surface to FL260; and is a vast area of airspace. There is a parachute jumping business that flies routinely in this sector. It is our procedure when they check on to assist in VFR flight following around their airport so that they may conduct their parachute operations safely. The aircraft knows to call Center to request a transponder code. We then issue the transponder code to the aircraft; radar identify the aircraft; give them an altimeter; verify their altitude and then advise them to advise Center of 'one minute prior to jumpers'; meaning they will advise one minute before they release any of their clients out of the aircraft. This one minute notification is to allow us to tell them about any traffic that may be between them and the airport that could interfere with the jumpers or the aircraft's descent. The jump aircraft appeared on my radar scope with their code. I tagged up his radar data block with the code and transmitted on the radio 'Aircraft X; radar contact 10 miles south of the ZZZ airport.... altimeter...say altitude and advise one minute prior.' Aircraft X responded with 'position checks; altitude...and we will give one minute.' As the aircraft is climbing up to altitude; I had Aircraft Y; an IFR overflight at 16000 feet; flying over the airport. I advised Aircraft X about the IFR traffic and I also advised them of the VFR aircraft climbing; and that they were a parachute jump aircraft. Neither aircraft had each other in sight; however they both said they were looking. Several seconds later; I continued my scan and took care of other matters in my sector. I returned to the traffic situation and saw that Aircraft X and turned directly towards Aircraft Y and was continuing his climb out of 15000 feet. I transmitted to Aircraft X 'Aircraft X; that IFR traffic is 12 o'clock and 3 miles; suggest you maintain one five thousand five hundred and I'll call when traffic is clear.' Aircraft X responded with a 'Roger; we are 1 minute prior to jumpers'. I responded to Aircraft X and told him other than that traffic; there was no other observed traffic between him and the airport. I then advised Aircraft Y that the jump aircraft would be maintaining 15500 feet. Aircraft Y acknowledged my transmission. After completing another scan of my radar scope I returned back to the traffic situation to see that Aircraft X in fact did NOT maintain 15000 feet; but continued to climb. I made another traffic call to Aircraft X 'Aircraft X; traffic 12 o'clock and immediately off of your nose' to which he replied 'Aircraft X; we can't see over our nose right now; we are 20 seconds to jumpers'. I advised him of the Aircraft Y traffic; AGAIN; terminated radar service; switched him from Center frequency and told him to report back up on his next jump. After terminating the radar for Aircraft X; the Aircraft Y keyed up and said 'Center; I thought that aircraft was stopping at one five thousand five hundred. That was a little too close for comfort; he missed us by maybe one hundred and fifty feet.' I did not acknowledge that aircraft at that point; but proceeded to catch up on the rest of my sector. Aircraft Y keyed up again several minutes later to ask what had happened and I apologized to the aircraft; and said that I thought the jump aircraft would be maintaining one five thousand five hundred and that I would speak with the pilot when he came back up.




Synopsis: ZDV Center Controller observed a VFR parachute jump aircraft climb through the altitude of an enroute IFR aircraft that the VFR aircraft had been advised of.