Date: 201503
Local time of day: 1801-2400
Location: CCR.Tower, CA
Light: Night
Aircraft: Small Aircraft
Flight plan: VFR
Flight phase: Final Approach
Airspace: Class D CCR
ATC / advisory: Tower CCR
Second aircraft: Small Aircraft
Reporter organization: Government
Reporter function: Supervisor / CIC; Flight Data / Clearance Delivery; Ground
Human factors: Confusion; Situational Awareness
Anomaly: ATC Issue All Types; Conflict NMAC; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Flight Crew Took Evasive Action
Contributing factors: Human Factors; Procedure
Primary problem: Procedure

Narrative: At the time of the event I was working; Ground Control; Flight Data; Clearance Delivery; and Controller-in-Charge combined. Traffic complexity and volume were average on Local Control; so I decided to monitor Local as much as I could. As I monitored I noticed two aircraft setting up on opposite bases for Runways 32R and 32L (these were the active runways at the time). The Cessna on right base for Runway 32R was Aircraft X and the Cessna on left base for Runway 32L was Aircraft Y. This is a routine; safe operation and if the Local Controller had allowed the aircraft to continue for their respective runways then the operation would have remained routine and safe. Instead; even though both aircraft are base to half mile final with approximately 500-700 feet of altitude; Local Control offers to change Aircraft Y to Runway 32R if they will turn back to the downwind to follow Aircraft X. After hesitating briefly Aircraft Y accepts Local's offer for Runway 32R. I do not know if Aircraft Y misunderstood Local's request to turn back to the downwind to follow Aircraft X or; because of the stage of flight Aircraft Y; could not comply. Whatever the case; Aircraft Y did not do as requested but instead; appeared to swerve to the right to avoid Aircraft X who was right base to half mile final for Runway 32R. And; even though Aircraft Y flew through final to come in behind Aircraft X the two aircraft still ended up in very close proximity to one another. In order to gain spacing Aircraft Y began executing several hard S-Turns all at low level (600 feet descending) and with only half a mile on final to the runway. At this time Aircraft X appeared to speed up; I believe; to gain spacing between themselves and Aircraft Y.Local did nothing to correct Aircraft Y when they failed to comply with his initial request to turn back to the downwind and; only belatedly approved Aircraft Y's S-Turns after they were already executing them. Nor did Local do anything to ensure the two aircraft would remain separated such as; cancelling Aircraft X's clearance for the Option and giving them a Touch-and-Go or Low Approach; or giving either aircraft a Go Around.In short; the Local Controller through poor judgment; bad phraseology; and lack of control instructions caused and unsafe situation to occur by; allowing these two aircraft to become too close to one another and; in so doing; causing the pilot(s) to execute extreme maneuvers at low altitudes on short final; increasing pilot workload in an already workload heavy stage of flight (i.e. landing). Worse of all the Local Controller did nothing to correct the situation he created or insured separation/safety. If the pilots of Aircraft Y and Aircraft X had not been aware and working as hard as they were to increase separation; Local would not have had proper Runway separation




Synopsis: Controller reports of observing a poor performance by the Local Controller resulting in a NMAC.