Date: 201702
Local time of day: 0601-1200
Location: SEE.Tower, CA
Flight conditions: VMC
Light: Daylight
Aircraft: Light Transport; Low Wing; 2 Turbojet Eng
Operator: Fractional
Operating under: Part 91
Flight plan: IFR
Flight phase: Initial Approach; Final Approach
Airspace: Class D SEE
ATC / advisory: Tower SEE
Second aircraft: Small Aircraft; High Wing; 1 Eng; Fixed Gear
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness; Distraction; Confusion; Communication Breakdown
Second reporter function: Pilot Flying; First Officer
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Became Reoriented
Contributing factors: Human Factors; Procedure
Primary problem: Procedure

Narrative: Aircraft X was on a LOC approach to Runway 27R. This is a circling approach. Aircraft X was asked if he wanted a straight in or circle to the runway. I informed the aircraft that a circle was standard. Aircraft X asked to circle. Aircraft X was instructed to maintain 1900 and to report over the numbers for Runway 27R. Aircraft X was then instructed to plan to circle 2 miles south to make a 3 1/2 base turn for runway 27R. At the numbers; Aircraft X was instructed to circle south (as indicated on the approach plates). 2 miles south Aircraft X was instructed to continue descent. Then I noticed Aircraft X turning west. Aircraft X was instructed to turn east via a left turn for a left base Runway 27R. Aircraft X stated that they thought they were going to Runway 09L. Once on left downwind Runway 27R Aircraft X was told about traffic inside of him for Runway 27L and to turn a 2 1/2 mile base and cleared to land Runway 27R. Aircraft X reported traffic in sight and cleared to land. Aircraft X cut off Aircraft Y turning a 1 mile base then asked who the traffic was on his right. Aircraft X was informed that the traffic was for Runway 27L and was going around. I then reconfirmed that Aircraft X was cleared to land Runway 27R. While Aircraft X was turning west he was within 1.4 NM and 700 feet of another aircraft on approach to MYF on an ILS approach. That aircraft was not in my control.This is a circling approach and although I have had no problems with other aircraft conducting this maneuver I could have reconfirmed with Aircraft X that they were to circle east for left downwind runway 27R.After sitting with the ATM and hearing the pilots thoughts and expectations for the approach it sounded like the pilot was expecting to land on another runway other that one advertised. The pilot stated that at their airport it is was common for an aircraft to make an approach to one runway then circle to a runway most aligned with the wind. When it was pointed out that the approach into SEE did not actually go to a runway that they were to circle to the runway in use the pilot seemed to have more clarity. This is a good opportunity to teach pilots that due to terrain some airports have other than standard approaches.


Second narrative: On a flight to SEE; we were cleared for the LOC-D circling approach into SEE. We were cleared to circle south at 1900 feet. We entered a left hand traffic pattern and landed runway 27R. We were notified later by the tower controller that we may have gotten too close to another aircraft during the circle maneuver. The other aircraft was not issued as traffic. The aircraft was never seen and there were no TAs observed.


Synopsis: SEE Local Controller and the involved pilots reported of confusion and an airborne conflict while on a circling approach.