Enroute controller described a possible loss of separation event between an IFR departure and an IFR...

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.

Original NASA ASRS Text

Title: 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.

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.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1004944
Time
Date	201204
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	Caravan Undifferentiated
Operating Under FAR Part	Part 135
Flight Phase	Initial Climb
Flight Plan	IFR
Aircraft 2
Make Model Name	Baron 58/58TC
Operating Under FAR Part	Part 135
Flight Phase	Final Approach
Route In Use	Visual Approach
Flight Plan	IFR
Person 1
Function	Enroute
Qualification	Air Traffic Control Fully Certified
Events
Anomaly	ATC Issue All Types Deviation - Procedural Clearance Deviation - Track / Heading All Types

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.