Narrative:

While working local control I was dealing with several IFR and VFR operations when approach called me up and asked if I could [take a] gulfstream and twin cessna; to which I asked; 'you mean visual?' 'affirmative' he said; and I said yes put them on me. The gulfstream inbound from the southeast to runway 16 and the twin cessna inbound for a straight in runway 16 approximately 9 miles to the north. Approach had already asked the twin cessna to reduce his airspeed and for the gulfstream to make a short approach prior to switching the aircraft to me. The first transmission I made was to the twin cessna and I told him to reduce his airspeed as he was number 2 following a gulfstream; and gave the gulfstream's position. I cleared the gulfstream to make a short approach and told him that he was inside of a twin cessna on a 6 mile final. Shortly afterward the twin cessna said that he had the gulfstream in sight. I made transmissions to different aircraft and then went back to the twin cessna. I again pointed out the gulfstream that he was following and cleared him to land following the gulfstream traffic. The twin cessna again indicated that he had the gulfstream in sight. The gulfstream turned approximately a half mile left base to final and was over the threshold when the twin cessna was approximately on a 3 mile final. Both the twin cessna and gulfstream landed without incident or complaint. After a review of the tapes it is clear that I was doing as everyone intended and anticipated. Although I did not know it at the time; approach had already given the twin cessna a speed reduction and the gulfstream a short approach. I was asked to provide visual separation to two aircraft that I could not apply visual separation to due to wake turbulence being involved. I was unaware of this at the time of the incident. I would also like to have heard the coordination that went on between meacham north and meacham south as they were each working one of the two aircraft inbound to the field but apparently coordinating verbally between each other. The rule specified in the 7110.65 7-2-1 indicates that visual separation cannot be applied to aircraft by a controller when wake turbulence is involved. After lengthy discussion with facility management and regional personnel I'm still a bit unclear as to how this rule is to be interpreted. The regional office has indicated that visual separation could have been applied in the situation if I would have only said; 'caution wake turbulence.' while I do not know how this would allow me to deviate from the 4 mile rule of a small following a large I do know that I should have issued a cautionary wake turbulence to aircraft arriving behind the large gulfstream. I would also like more specific references to be included in training materials such as wake turbulence computer based instruction's that relate to the incident described. After discussion amongst facility personnel we could not remember specifics concerning visual separation when wake turbulence is involved. There are still many different people interpreting this rule in different ways. Again I go back to the solution apparently being that all I would have had to say was caution wake turbulence and continued to apply visual separation. If this is the case then I feel that it will enlighten many controllers who do not interpret it this way.

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Original NASA ASRS Text

Title: Tower Controller agreed to provide visual separation between two arrival aircraft realizing later that wake turbulence separation was not covered as part of the procedure being utilized.

Narrative: While working Local Control I was dealing with several IFR and VFR operations when Approach called me up and asked if I could [take a] Gulfstream and twin Cessna; to which I asked; 'You mean visual?' 'Affirmative' he said; and I said yes put them on me. The Gulfstream inbound from the southeast to Runway 16 and the twin Cessna inbound for a straight in Runway 16 approximately 9 miles to the north. Approach had already asked the twin Cessna to reduce his airspeed and for the Gulfstream to make a short approach prior to switching the aircraft to me. The first transmission I made was to the twin Cessna and I told him to reduce his airspeed as he was number 2 following a Gulfstream; and gave the Gulfstream's position. I cleared the Gulfstream to make a short approach and told him that he was inside of a twin Cessna on a 6 mile final. Shortly afterward the twin Cessna said that he had the Gulfstream in sight. I made transmissions to different aircraft and then went back to the twin Cessna. I again pointed out the Gulfstream that he was following and cleared him to land following the Gulfstream traffic. The twin Cessna again indicated that he had the Gulfstream in sight. The Gulfstream turned approximately a half mile left base to final and was over the threshold when the twin Cessna was approximately on a 3 mile final. Both the twin Cessna and Gulfstream landed without incident or complaint. After a review of the tapes it is clear that I was doing as everyone intended and anticipated. Although I did not know it at the time; Approach had already given the twin Cessna a speed reduction and the Gulfstream a short approach. I was asked to provide visual separation to two aircraft that I could not apply visual separation to due to wake turbulence being involved. I was unaware of this at the time of the incident. I would also like to have heard the coordination that went on between Meacham North and Meacham South as they were each working one of the two aircraft inbound to the field but apparently coordinating verbally between each other. The rule specified in the 7110.65 7-2-1 indicates that visual separation cannot be applied to aircraft by a controller when wake turbulence is involved. After lengthy discussion with Facility Management and Regional Personnel I'm still a bit unclear as to how this rule is to be interpreted. The Regional Office has indicated that visual separation could have been applied in the situation if I would have only said; 'caution wake turbulence.' While I do not know how this would allow me to deviate from the 4 mile rule of a small following a large I do know that I should have issued a cautionary wake turbulence to aircraft arriving behind the large Gulfstream. I would also like more specific references to be included in training materials such as wake turbulence Computer Based Instruction's that relate to the incident described. After discussion amongst facility personnel we could not remember specifics concerning visual separation when wake turbulence is involved. There are still many different people interpreting this rule in different ways. Again I go back to the solution apparently being that all I would have had to say was caution wake turbulence and continued to apply visual separation. If this is the case then I feel that it will enlighten many controllers who do not interpret it this way.

Data retrieved from NASA's ASRS site as of April 2012 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.