Citationjet (C525/C526) - CJ I / II / III / IV
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 8
Communication Breakdown; Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification
Chart Or Publication; Airspace Structure; Procedure; Company Policy
Aircraft X was inbound on a Visual Approach with two VFR targets on 1200 codes northbound near east of Class D airspace. As Aircraft X checked on; I heard the Local Controller issuing traffic and I believe Aircraft X reported traffic in sight. One target was north of the final and no longer a factor; however there was also a second target (Aircraft Y) near the final; also northbound around 7300 ft.Aircraft X asked what the intentions of the traffic above him were; and the tower controller responded that intentions were unknown because the aircraft (Aircraft Y) had not established communications and appeared to be transitioning east of the Class D airspace. Aircraft X responded 'not good'. Aircraft Y established communications after that. The transitioning aircraft reported that he was aware of the traffic on final as he transitioned in the VFR corridor; and the Tower Controller suggested to the transitioning aircraft in the future he may want to communicate with ATC due to the volume of traffic in the area. Aircraft Y acknowledged he would in the future. A MOR (Mandatory Occurrence Report) was also filed as a 'public inquiry' due to the concern expressed by Aircraft X about proximity of the other traffic. This is one more event highlighting concern about the design of this airspace corridor; where VFR aircraft operate without communication with ATC. In situations like these; such aircraft skirting controlled airspace can create conflicts with aircraft transitioning from Approach over to the Tower frequency. In fact; in the event of an inoperative transponder; we might not even know such transitioning aircraft were even there! Many of these conflicts could be mitigated and managed better if aircraft operating so close to Class B and Class D airspace would communicate with ATC; or if controlled airspace was redesigned to ensure aircraft could not operate in this area or at those higher altitudes without first establishing communication with ATC.
BJC Tower Controller reported that an aircraft on visual approach was concerned that an aircraft in a VFR corridor was too close.