Date: 201303
Local time of day: 1801-2400
Location: ZMA.ARTCC, FL
Aircraft: Eclipse 500
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Descent
Airspace: Class A ZMA
ATC / advisory: Center ZMA
Second aircraft: Challenger CL600
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Human-Machine Interface; Situational Awareness
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
Result: Air Traffic Control Issued New Clearance
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: Aircraft X and Aircraft Y were both RSW landing aircraft. Aircraft X was number one in the sequence and descending out of FL290 to FL270. Aircraft X had a fourth line speed of 310+ to stay in front of Aircraft Y; while Aircraft Y had fourth line data input of 300-. The ZJX Controller had Aircraft Y on a southwesterly heading to provide more spacing with Aircraft X. I had accepted the hand off on both aircraft at this time. Less than a minute later; Aircraft Y was turned back on course. As I made my scan I saw the ground speed on Aircraft X showing 521 while the aircraft in trail showed 430 knots as the aircraft was still rolling out of the turn. Since there were fourth line entries; I was not able to see the type aircraft. Aircraft X was not able to maintain that speed or at the very least very slowly increasing speed to reach it. As I continued my scan I realized that Aircraft X was flashing a bad beacon code and time sharing information with his actual ground speed which I realized was actually 386 knots. Aircraft Y was indicating 470 knots and quickly catching the Aircraft X with a 100 knot overtake. As soon as I realized the actual ground speeds; separation had dropped to 4.7 miles and 0ft. Aircraft X was directly on the mutual boundary with me and the ZJX sector the aircraft was coming from. I cleared Aircraft X to descend to FL260 and Aircraft Y to turn 30 degrees right and reduce speed as I called traffic to the aircraft. Aircraft Y was still 3 miles from my airspace but I had no other choice but to turn the aircraft in order to reestablish separation. This situation occurred due to poor vectoring and speed control from the previous sector. The event occurred in ZJX airspace and could only be stopped by the ZJX Controller as the aircraft were running 5.5 miles and rapidly decreasing as it approached my sector. Because of the massive overtake the aircraft could not have been turned in time to prevent the loss of separation unless it had been done before by the previous Controller. By the time it occurred there was no time to make a phone call to the ZJX Controller to alert them to the turning of Aircraft Y and the descent of Aircraft X. I had no D-Side and was working alone. This was very unfortunate in the way it happened. The aircraft had been put on a vector for the exact reason to avoid the error and assigned a speed. It was turned back too soon and the assigned speeds had not taken affect. The prevention of this error mostly comes down to better use of vectoring and speed control from the delivering Controller. A contributing factor was that the fourth line data was blocked due to the assigning of speeds. Seeing that an E55P in front of a CL60 would be a cause for concern when two aircraft are being run that tight. Also; the bad beacon code being mistaken for the speed of 521 knots instead the actual 386 knots needed to be caught earlier. My recommendation is to always; always; always; use vertical separation until speed control is taking effect. I would have gladly accepted the back aircraft 1;000 feet higher than have him overtake a slower moving aircraft at the same altitude with no time to turn and not even in my airspace. You can never go wrong with vertical separation.




Synopsis: ZMA Controller described a loss of separation event between two aircraft by being transferred from ZJX caused an overtake speed differential; the reporter recommending that altitude be used until in-trail separation can be assured.