Date: 201204
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Aircraft: Caravan Undifferentiated
Operator: Air Taxi
Operating under: Part 135
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Initial Climb
Airspace: Class D ZZZ
ATC / advisory: Center ZZZ
Second aircraft: Baron 58/58TC
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness
Anomaly: ATC Issue All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
Result: General None Reported / Taken
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: A Baron was inbound at 5;000 looking for a Visual Approach to the runway. Tower called requesting clearance on a Caravan off the runway; the Tower Controller said that he was ready to go off the runway. I asked if he could be off in 1.5 minutes or less; Tower said yes. I based my decision on the fact that it would be more than 2 minutes before the Baron would be adjacent to the airport thus they would always be at the very least parallel to one another without being converging in any way. I also thought that the Caravan would depart and turn shortly after departure; which is normally what they do when given direct their destination. Since it was extremely VFR and great visibility; I also told the Baron that he could turn to the right to set up for a base to the runway. I'm not sure of the time of departure; but the Caravan did not turn on course direct their destination as expected; and it actually appeared as though he turned south; I questioned him and told him it appeared he flew a 200 heading; not the 240 heading that they normally fly off the runway. The Baron didn't turn to the right at all to set up for base. Since I had already cleared the Baron for the Visual Approach; and he was below the MVA; I couldn't legally vector the aircraft; but at this point I was pretty sure that we were going to have at least 3 miles and that safety wasn't compromised. Both aircraft were on my frequency and diverging. I issued once again direct their destination when able and then the Baron turned direct to the Caravan's destination. I don't know if he was flying the departure procedure assigned by Tower; or if he just flew it on his own. I could have told Tower to just hold the Caravan on the ground; but I've done this thousands of times and have never really had a problem. I was told that the Caravan was ready to go and I couldn't see having him wait unnecessarily. I also could have vectored the Baron to the right and left him at the MVA (4;200) until I got the Caravan in RADAR contact and then cleared him for approach. There was no chance of the 2 aircraft ever hitting. I think that we should be able to use 3 miles around airports that we provide approach services to.




Synopsis: Enroute Controller described a possible loss of separation event between an IFR departure and an IFR inbound aircraft cleared for a Visual Approach; the event occurring during approach services to a VFR Towered airport.