Air Traffic Control Fully Certified
Situational Awareness; Confusion; Communication Breakdown
ATC Issue All Types; Conflict NMAC
General None Reported / Taken
Human Factors
A C172 checked on my frequency with the intent to land PRC. I issued standard pattern entry instructions per local directives for the current runway configuration and airspace delegation. The instructions issued were for left traffic Runway 12. A second C172; checked on my frequency from the other Local Control position on departure heading 15 degrees left of runway heading. The VFR departure strip I had in front of me indicated the aircraft was requesting an eastbound departure. There was additional traffic; a helicopter; not involved with this report but was a factor for the second C172. After the helicopter traffic vs. the C172 was resolved; I issued instructions to the C172 to proceed on course which I expected to be eastbound. At this time the first C172 was inbound on the left 45 VFR pattern entry talking to the other Local Controller for descent and landing instructions. The second C172 actually turned to an approximate heading of 010; northeast bound; a flight path that conflicted with the first C172. I continued to work additional in-bounds and diverted my attention from the second C172. Moments later I received a report from the second C172 that they were passing under the first C172 by about 100 FT and that they have them in sight. I acknowledged the report; visually acquired both aircraft; and notified the other Local Controller of the traffic who was working the first C172 inbound. Recommendation; there were multiple factors that led to this event. The non-verbal coordination written on the VFR departure strip indicating the aircraft was requesting an eastbound departure was incorrect. My instructions to the aircraft were not specific enough; 'on course approved; rather than eastbound approved'; to listen and verify that the aircraft would comply. Traffic volume and complexity were both building at the time and my attention could not be fully applied to the second C172.
PRC Controller described a pattern conflict event when the internal Tower coordination failed.