Narrative:

Aircraft X was in the local traffic pattern at night. They completed one touch and go and asked to orbit on the downwind to troubleshoot a problem. Several arrivals were being vectored inbound advertising the approach to the runways which all intersect at some point with one other runway. TRACON called and asked to send a local police aircraft direct to the field I am assuming to get them in front of the other jets that were coming in; I approved. Aircraft X advised they finished troubleshooting and would like to come make another touch and go to the runway so I had them rejoin the downwind advised them they would be behind the first arrival and in front of aircraft Y; who was still approximately 15 plus miles northwest of the airport. First arrival being in a C172 is slow; but the spacing was there; so I called TRACON to advise them I was putting aircraft X between the first arrival and aircraft Y. I was scanning and planning ahead waiting to call aircraft X's base turn. By the time I called aircraft X's base; aircraft Y had never slowed and indicated over 200 knots; and was not switched to me until 5 miles nor were they aware of aircraft X or his intentions; so I quickly had to tell him aircraft X was a heavy option to the runway in front of them they said they have them insight. I had to get the first arrival off the runway and with just at 3 miles between aircraft X and aircraft Y (maybe slightly less). I instructed aircraft X to do a low approach only to keep him moving in hopes aircraft Y would not close in any more on aircraft X. I am unsure of if aircraft Y was on the visual approach; I believe they were; but I was instructed that I did not tell aircraft Y to maintain visual separation from aircraft X when this event was brought to my attention. However if aircraft Y was on a visual approach that is not necessary; but if he was on an instrument approach and I thought wrong then there is the issue in not saying those specific words regardless of if he had aircraft X in sight.I should have expedited the first arrival more or not approved the request. I could have possibly extended aircraft X's downwind thought that would have put him right between both finals with crossing traffic; I also could have called TRACON and asked for control of aircraft Y and have him put on my frequency earlier to advise them earlier of the situation and then perhaps my gap I thought I had would have stayed there and it wouldn't have shrunk as much as it did.

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Original NASA ASRS Text

Title: Local Controller had a large aircraft behind a heavy aircraft with less than the required wake turbulence separation. The large aircraft had the preceding traffic in sight; but was never instructed to 'maintain visual separation.'

Narrative: Aircraft X was in the local traffic pattern at night. They completed one touch and go and asked to orbit on the downwind to troubleshoot a problem. Several arrivals were being vectored inbound advertising the approach to the runways which all intersect at some point with one other runway. TRACON called and asked to send a local police aircraft direct to the field I am assuming to get them in front of the other jets that were coming in; I approved. Aircraft X advised they finished troubleshooting and would like to come make another touch and go to the runway so I had them rejoin the downwind advised them they would be behind the first arrival and in front of Aircraft Y; who was still approximately 15 plus miles northwest of the airport. First arrival being in a C172 is slow; but the spacing was there; so I called TRACON to advise them I was putting Aircraft X between the first arrival and Aircraft Y. I was scanning and planning ahead waiting to call Aircraft X's base turn. By the time I called Aircraft X's base; Aircraft Y had never slowed and indicated over 200 knots; and was not switched to me until 5 miles nor were they aware of Aircraft X or his intentions; so I quickly had to tell him Aircraft X was a heavy option to the runway in front of them they said they have them insight. I had to get the first arrival off the runway and with just at 3 miles between Aircraft X and Aircraft Y (maybe slightly less). I instructed Aircraft X to do a low approach only to keep him moving in hopes Aircraft Y would not close in any more on Aircraft X. I am unsure of if Aircraft Y was on the visual approach; I believe they were; but I was instructed that I did not tell Aircraft Y to maintain visual separation from Aircraft X when this event was brought to my attention. However if Aircraft Y was on a visual approach that is not necessary; but if he was on an instrument approach and I thought wrong then there is the issue in not saying those specific words regardless of if he had Aircraft X in sight.I should have expedited the first arrival more or not approved the request. I could have possibly extended Aircraft X's downwind thought that would have put him right between both finals with crossing traffic; I also could have called TRACON and asked for control of Aircraft Y and have him put on my frequency earlier to advise them earlier of the situation and then perhaps my gap I thought I had would have stayed there and it wouldn't have shrunk as much as it did.

Data retrieved from NASA's ASRS site 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.