Narrative:

Aircraft X was on a practice ILS approach. On the missed approach; I issued runway heading for a jet that would be departing behind and turning northeast. Aircraft Y was told about aircraft X ahead of him on the departure end of the runway and that he would be turning inside that aircraft; then cleared him for takeoff heading 060. When aircraft Y was on a roughly half mile departure he advised me; and I could also see using tower applied visual separation; that he was in the right turn and absolutely no factor for aircraft X. When aircraft Y was well established in the turn; as was visually assured out the window; I shipped him to departure control. Once I visually observed aircraft Y well established in the right turn to 060; I told aircraft X to turn right heading 040; which is the standard missed approach as per the letter of agreement with TRACON and 20 degrees outside of aircraft Y who made his 060 turn immediately after departure. Both aircraft knew about each other's intent. Runway separation was applied prior to using visual separation; and then departure degree divergence was applied after visual separation.I firmly believe that there is no issue with this operation and this report is being filed reference a mandatory occurrence report. Things look very different looking out a window to separate aircraft than they do on a radar scope having both tower and radar experience. This is simply an alarm based on radar environment rules when VFR tower operations were being applied in a completely safe manner. I don't have a recommendation. Just too please be aware that VFR towers are using tower applied visual separation differently than visual is used in a radar environment.

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Original NASA ASRS Text

Title: A Tower Controller reported following all the guidelines for Tower Visual Separation and Degrees Divergence rules that may have been considered as an operational error.

Narrative: Aircraft X was on a practice ILS approach. On the missed approach; I issued runway heading for a jet that would be departing behind and turning northeast. Aircraft Y was told about Aircraft X ahead of him on the departure end of the runway and that he would be turning inside that aircraft; then cleared him for takeoff heading 060. When Aircraft Y was on a roughly half mile departure he advised me; and I could also SEE using TOWER Applied Visual Separation; that he was in the right turn and absolutely no factor for Aircraft X. When Aircraft Y was well established in the turn; as was VISUALLY assured out the window; I shipped him to Departure Control. Once I visually observed Aircraft Y well established in the right turn to 060; I told Aircraft X to turn right heading 040; which is the standard missed approach as per the Letter of Agreement with TRACON and 20 degrees outside of Aircraft Y who made his 060 turn IMMEDIATELY after departure. Both aircraft knew about each other's intent. Runway Separation was applied prior to using visual separation; and then Departure Degree Divergence was applied after visual separation.I firmly believe that there is no issue with this operation and this report is being filed reference a Mandatory Occurrence Report. Things look VERY different looking out a window to separate aircraft than they do on a RADAR scope having both Tower and RADAR experience. This is simply an alarm based on RADAR environment rules when VFR Tower operations were being applied in a completely safe manner. I don't have a recommendation. Just too please be aware that VFR Towers are using Tower Applied Visual Separation differently than Visual is used in a RADAR environment.

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.