B737-700
Air Traffic Control Fully Certified
Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Clearance
Flight Crew Took Evasive Action
Procedure; Human Factors
Working South Local Control and had a pre-coordinated survey aircraft (a PA31) flying grid patterns that were taking him east and west across the north side of the airport and across the finals. I had already had to ask the PA31 to do one 360 turn off the grid to get clear of a Runway 11 arrival when this event occurred. After resuming the grid run; the PA31 was flying east at 2;500 FT and towards the Runway 12L final. A B737 was then inbound for Runway 12L from the northwest descending out of 3;000. I issued traffic to the PA31 and he reported the B737 in sight and that he would maintain visual separation with that traffic. I also issued the PA31 traffic to the B737 and told him that the PA31 was maintaining visual separation with him. The 2 aircraft continued to converge and I again told the PA31 to maintain visual separation and he agreed. As targets began to merge; it was apparent that the PA31 was not going to change altitude or direction. The B737 descended to pass beneath the PA31 when at a better than normal rate. After the B737 landed; he wanted to pass along his displeasure with the PA31 and the entire operation that had occurred. The PA31 was still on the frequency and I asked him if he heard the complaint. He responded that he did. That was the last of the conversation. The PA31 was asked to find a different set of grid lines to work other than the ones he was flying. He moved his grid pattern further south and stopped flying over the finals. The bigger problem here was the acceptance of visual separation by the PA31 and then the subsequent; almost refusal; to deviate from the grid to avoid the traffic that was issued. It did not appear from looking out the window; that the PA31 ever made an attempt to maneuver away from the B737 and that the B737 had to provide the separation even though he had been told that the PA31 was maintaining visual separation from him. I really don't know what to recommend other than a stern talking to by FSDO to the PA31 pilot? In the future; I will be turning this PA31 away from the traffic and not give him the option to visually separate himself.
Tower Controller described a conflict when traffic conducting a survey operation agreed to maintain visual separation with an inbound air carrier; but continued on the grid pattern requiring the air carrier to initiate evasive action/s.